JP2010171571A - Image processor, image processing method, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To display an image of a zone where a gradation value is extremely gently changed as a high-quality image whose gradation change looks smooth by real-time signal processing without remarkably increasing a circuit scale. <P>SOLUTION: This image processor includes: a gradation change detection means 10 to obtain a gradation change amount dfx, an amplitude-limited gradation change amount Xlm, and a gradation change position signal Pt; a flatness width prediction means 20 to generate a flatness width data prediction value dst from a low frequency component of the flatness width of a gradation flatness zone; an inclination detection means 40 to obtain an inclination data value Ksl from the change amount Xlm and the flatness width data prediction value dst; a correction restriction coefficient setting means 30 to set a correction restriction coefficient rc from the gradation change amount dfx; a correction bit generation means 50 to generate correction bit data Cd based on the change amount Xlm, the inclination data value Ksl, and the correction restriction coefficient rc; and a pixel value calculation means 62 to add or subtract the correction bit data Cd to/from an input image signal Da, and output an image signal Db obtained by expanding a gradation number and correcting a gradation value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image processing method for generating an output image signal composed of data in which the number of gradations is expanded by extending the number of gradations of data of each pixel of an input image signal, and the image The present invention relates to an image display device to which a processing device or an image processing method is applied.

  Devices such as liquid crystal, plasma, EL (electroluminescence), DMD (digital mirror device), etc., display images by modulating matrix pixels arranged discretely by reflection or transmission of light or light emission. It is used in various image display devices (displays) such as flat-screen televisions, projection televisions, projectors, and computer monitors. In recent years, high-definition broadcasting and computer processing speed have been improved, and the display has been improved in definition, and display has been rapidly increased in brightness due to device improvements. On the other hand, the number of gradations (bits) that can be displayed is expanded as the display brightness increases, so users can identify subtle gradation differences between pixels when displaying digitized image signals. Quantization noise has become prominent.

  When receiving an analog image signal, the number of bits of the digital signal after conversion by the analog-to-digital converter is increased (for example, the number of bits that was conventionally 8 bits is increased to 10 bits), and quantization is performed. It is possible to reduce noise. However, in a display capable of displaying a high-definition image, increasing the speed of the analog-digital converter and increasing the number of quantizations involve a significant cost increase.

  When a digital image signal is received (for example, in the case of digital television broadcasting), an image signal having a quantization number determined by an agreement between a transmission side and a reception side in digital transmission is transmitted / received (generally, 8 By performing bit quantization, an 8-bit gradation image signal is generated), and the quantization number cannot be changed unless the agreement is changed. Similarly, since the number of quantizations is also determined in advance for digital contents on DVDs and networks, the number of quantizations of the contents themselves cannot be increased unless a new standard is provided.

  Furthermore, in image signal processing for televisions and the like, processing for expanding the dynamic range of received image signals in order to display high-impact video, and conversion to high-contrast video by changing the tone-brightness conversion characteristics Processing is in progress. When such gradation correction processing is performed, a high-contrast video can be displayed, while gradation skip (gradation jump) occurs due to gradation correction, and quantization noise increases.

  In such a case, as a method of reducing the quantization noise of the image signal by digital image processing, a gradation conversion technique (multi-gradation technique) that increases the number of gradations of the image signal by adding lower bits to the image signal. ) As this gradation conversion technique, a technique has been proposed in which a signal having a specific gradation change in an image signal is detected and the number of gradations is expanded for the detected necessary pixels.

  For example, Japanese Patent Laid-Open No. 2003-304400 (Patent Document 1) uses an image memory to detect the same luminance region that is a set of adjacent pixels at the same luminance level in an image signal from the image memory, A boundary between adjacent identical luminance regions based on the determination result of the false contour detector that determines whether the difference in luminance level between adjacent identical luminance regions matches a preset value or not An image processing apparatus including a pixel value converter that converts a luminance level of a pixel in the vicinity to a halftone is disclosed.

  Further, in Japanese Patent No. 3710131 (Patent Document 2), the detection means has a low-frequency portion of the input image signal from the line memory (a plurality of first pixel values are continuous, and a predetermined level pixel from the first pixel value). The second pixel value having a changed value is detected in a plurality of consecutive portions), and the signal extension means adds a predetermined number of bits to the bit string of the first or / and second pixel value in the predetermined range of the low frequency portion. An image processing apparatus is disclosed that performs the extended correction so that the pixel values sequentially change.

  Further, Japanese Patent Laid-Open No. 2007-158847 (Patent Document 3) sequentially inputs video signals to a shift register, and uses a pixel signal held in the register so that the signal level difference is within a preset signal level difference. When the signal level difference is, for example, 1 bit, a continuous pixel equal to the signal level of the pixel immediately before the signal level difference is determined is determined. On the other hand, there has been proposed a gradation conversion device that sets the amount of change in signal level between pixels by averaging, and generates a video signal by assigning bits based on the set amount of change.

  Further, Japanese Patent No. 34559797 (Patent Document 4) includes means for specifying the first and second image levels having a gradation jump in the middle among the image levels included in the gradation conversion image data. First contour data indicating a boundary between a region having the first image level and another region having an image level lower than the first image level is obtained, and the region having the first image level and the second Means for obtaining second contour data indicating a boundary with another region having an image level equal to or higher than the image level, and a region adjacent to the image region having the second image level in the region having the first image level Is detected as a target region for gradation interpolation, and at least one set of contour lines indicating the contour of the target region is extracted from each type of contour line, and in the target region, During ~ Each type of outline is partitioned into (N + 1) (N is an integer greater than or equal to 1) segmented regions, and N (N + 1) segmented regions that are close to the image region of the second image level. A gradation interpolating device has been proposed that includes means for sequentially assigning N intermediate image levels to a segmented region.

JP 2003-304400 A (summary, FIG. 1) Japanese Patent No. 3710131 (FIGS. 2 to 4) JP 2007-158847 A (summary, FIGS. 2 and 12) Japanese Patent No. 34559797 (Claim 10, FIGS. 1 to 6)

  In the above-described conventional apparatus, a configuration in which an image memory corresponding to the pixel width of the continuous area to be detected is provided and detected is a gradation change position where a difference between the gradation values is constant and a continuous area of the same gradation value. The gradation change of the specified region is configured by searching in advance for the combination of gradations in which the gradation jump occurs, and specifying the region in the image signal where the combination of gradations in which the gradation jump occurs is adjacent. On the other hand, the number of gradations is expanded by interpolation so as to increase the number of bits of the image signal.

  In addition, as described above, an image signal in a television broadcast, a DVD, digital content on a network, or the like is input to the image processing apparatus as a signal having a predetermined quantization number (bit number). Therefore, when the number of bits of the image signal is smaller than the number of bits that can be displayed on the display, or when a gradation jump occurs due to image processing such as gradation correction processing, there is essentially no contour (edge) of the image. There is a problem in that a stripe pattern that does not originally exist is perceived as a pseudo contour (also referred to as a “pseudo contour”) in an image region where the gradation changes gradually.

  Further, in the above conventional apparatus, an image memory is used when performing an interpolation process for detecting a change in gradation in a specified region having a pseudo contour or a gradation jump and extending the number of gradations. Large memory is required to detect image areas where gradation changes more slowly and search for wider gradation jump areas to increase the number of bits in the image signal and reduce quantization noise in the image signal Therefore, there is a problem that the circuit scale of the image processing apparatus increases and becomes expensive.

  Furthermore, as in the case of televisions or the like, image signals sent continuously in time need to be processed in real time, but image processing that requires a large amount of memory can be performed in real time. It was difficult to do with.

  Furthermore, in an actual image processing apparatus, the size and processing time of the memory that can actually be used are limited, so that it is not possible to detect appropriate gradation changes, and gradation conversion processing that expands the number of gradations. However, there is a problem that gradation change cannot be obtained as a smooth image signal, quantization noise or pseudo contour of the image signal cannot be reduced well, and image quality is deteriorated.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is to provide a very gentle gradation value by real-time signal processing without greatly increasing the circuit scale. An object of the present invention is to provide an image processing apparatus and an image processing method capable of generating an output image signal for displaying an image in a changing section as a high-quality image with a smooth gradation change.

  Another object of the present invention is to provide a high-quality image with a smooth gradation change in an image in which the gradation value changes very slowly by real-time signal processing without greatly increasing the circuit scale. An object of the present invention is to provide an image display device that can display as a simple image.

  The image processing apparatus according to the present invention receives an input image signal composed of discrete data in the time direction and the space direction, and generates the input image signal by conversion processing that expands the number of gradations and corrects the gradation value. An image processing apparatus having a function of outputting an output image signal composed of the converted data, and a gradation change amount that is a difference between gradation values of pixels arranged adjacent to each other from the input image signal The gradation change detecting means for detecting gradation change information including a gradation change position that is a pixel position where the value of the gradation change amount is not 0, and the pixel at the gradation change position is determined from the gradation change information. A means for generating a flat width data predicted value, which is a predicted value of a flat width of a gray level flat section immediately after the reference pixel, using the detected pixel at the gradation change position as a reference pixel each time it is detected. The same gradation value immediately before the reference pixel Based on the flat width of the gradation flat section where the pixels are continuous and the previous flat width data prediction value generated in the immediately preceding reference pixel detected immediately before the reference pixel, the gradation flat section immediately after the reference pixel is calculated. A flat width predicting unit that generates a flat width data prediction value that predicts a flat width, and after the conversion in the gray level flat section immediately after the reference pixel, based on the gray level change information and the flat width data predicted value. An inclination detecting means for obtaining an inclination data value used when setting an inclination of a gradation value of data, and a gradation change at the gradation change position based on the gradation change amount is a gradation change caused by an edge of the image. Correction limit coefficient setting means for setting a correction limit coefficient for limiting the gradient of the gradation value of the output image signal according to the determination result, the gradation change information, and the gradient data value The above correction system A correction bit generation means for obtaining a correction value of a gradation value of the input image signal using a coefficient and generating correction bit data corresponding to the correction value, and according to the correction bit data for the gradation value Pixel value calculation means for generating the output image signal composed of the converted data by subtracting or adding the obtained values.

  Also, the image processing method of the present invention is a conversion process in which an input image signal composed of discrete data in the time direction and the spatial direction is input, the number of gradations of the input image signal is expanded, and the gradation value is corrected. An image processing method for outputting an output image signal composed of post-conversion data generated by the method, wherein a gradation change amount that is a difference between gradation values of pixels arranged adjacent to each other from the input image signal A gradation change detecting step for detecting gradation change information including a gradation change position that is a pixel position where the value of the gradation change amount is not 0, and the pixel at the gradation change position is detected from the gradation change information A step of generating a flat width data predicted value, which is a predicted value of a flat width of a gray level flat section immediately after the reference pixel, by using the detected pixel of the gradation change position as a reference pixel each time , The same floor immediately before the reference pixel Gradation flattening immediately after the reference pixel based on the flat width of the flat gradation interval in which pixels of the value are continuous and the previous flat width data predicted value generated in the immediately preceding reference pixel detected immediately before the reference pixel. A flat width prediction step for generating a flat width data prediction value that predicts a flat width of the section, and the gradation flat section immediately after the reference pixel based on the gradation change information and the flat width data prediction value. An inclination detection step for obtaining an inclination data value used when setting the inclination of the gradation value of the converted data, and the gradation change at the gradation change position based on the gradation change amount is a gradation change caused by an edge of the image. A correction limiting coefficient setting step for setting a correction limiting coefficient for limiting the gradient of the gradation value of the output image signal according to the determination result, the gradation change information, and the inclination data. A correction bit generation step for obtaining a correction value of a gradation value of the input image signal using the value and the correction restriction coefficient, and generating correction bit data corresponding to the correction value; And a pixel value calculation step of generating the output image signal composed of the converted data by subtracting or adding a value corresponding to the correction bit data.

  Furthermore, an image display device of the present invention includes the image processing device and display means for displaying an image based on the output image signal in which the number of gradations supplied from the image processing device is expanded.

  According to the image processing apparatus and the image processing method of the present invention, with respect to the input image signal, the number of gradations of the image signal is expanded and the gradation value is appropriately corrected in a section where the gradation value changes very gently. Since the output image signal is generated by performing the gradation conversion processing, the image in the interval where the gradation value changes very slowly by real-time signal processing without significantly increasing the circuit scale. There is an effect that it is possible to generate an output image signal that can be displayed as a high-quality image with a smooth tone change.

  In addition, according to the image display device of the present invention, for the input image signal, the gradation level of the image signal is expanded and the gradation value is appropriately corrected in a section where the gradation value changes very gently. Tone conversion processing is performed to generate an output image signal, and an image based on this output image signal is displayed. Therefore, an image in a section where gradation values change very slowly can be displayed with high quality with smooth gradation changes. There is an effect that it can be displayed as a simple image.

It is a block diagram which shows roughly an example of a structure of the image processing apparatus by Embodiment 1 and 2 of this invention. (A)-(c) is a figure which shows an example of the signal waveform (when the gradation value of an input image signal raises gradually) in the image processing apparatus by Embodiment 1, (a) is 8 bits. (B) shows the gradation change amount and gradation change position of the input image signal, and (c) shows the gradation number expanded and the gradation level. The gradation value near the least significant bit of the 12-bit output image signal whose tone value is corrected is shown. (A)-(c) is a figure which shows an example of the signal waveform (when the gradation value of an input image signal falls gradually) in the image processing apparatus by Embodiment 1, (a) is 8 bits. (B) shows the gradation change amount and gradation change position of the input image signal, and (c) shows the gradation number expanded and the gradation level. The gradation value near the least significant bit of the 12-bit output image signal whose tone value is corrected is shown. It is a block diagram which shows roughly an example of a structure of the flat width estimation means shown by FIG. It is a block diagram which shows roughly an example of a structure of the correction | amendment limiting coefficient setting means shown by FIG. It is a figure which shows an example of operation | movement of the coefficient conversion means shown by FIG. (A) And (b) is a figure which shows the example of the gradation change detected by the correction | amendment restriction coefficient setting means shown by FIG.1 and FIG.5. It is a block diagram which shows roughly an example of a structure of the inclination detection means shown by FIG. (A) And (b) is a conceptual diagram for demonstrating the inclination data value calculated by the inclination detection means shown by FIG.1 and FIG.8. It is a block diagram which shows roughly an example of a structure of the correction | amendment bit production | generation means shown by FIG. It is a figure for demonstrating operation | movement of the pixel value calculating means shown by FIG. It is a flowchart which shows operation | movement of the gradation conversion means shown by FIG. (A)-(k) is a figure for demonstrating an example (when a gradation value rises very gently) of the operation | movement of the gradation conversion means shown by FIG. (A)-(k) is a figure for demonstrating an example (when a gradation value falls very gently) of operation | movement of the gradation conversion means shown by FIG. It is a figure for demonstrating operation | movement of the gradation conversion means of the image processing apparatus by Embodiment 2 of this invention. (A)-(l) is a figure for demonstrating an example of operation | movement of the gradation conversion means of the image processing apparatus by Embodiment 2. FIG. It is a block diagram which shows roughly an example of a structure of the image processing apparatus by Embodiment 3 of this invention. (A) And (b) is a figure which shows the example of the change of the gradation value for demonstrating operation | movement of the continuous change determination means of the image processing apparatus by Embodiment 3. FIG. (A) And (b) is a figure which shows the other example of the change of the gradation value for demonstrating operation | movement of the continuous change determination means of the image processing apparatus by Embodiment 3. FIG. FIG. 10 is a block diagram schematically illustrating an example of a configuration of a continuous change determination unit of an image processing apparatus according to a third embodiment. FIG. 10 is a block diagram schematically showing an example of the configuration of correction bit generation means of an image processing apparatus according to Embodiment 3. 14 is a flowchart showing the operation of the gradation conversion means of the image processing apparatus according to the third embodiment. It is a block diagram which shows roughly an example of a structure of the image processing apparatus by Embodiment 4 of this invention. FIG. 24 is a block diagram schematically showing an example of the configuration of the vertical direction gradation converting means shown in FIG. 23. FIG. 25 is a diagram for explaining a relationship between pixel positions in the vertical direction of an image signal in the vertical direction gradation converting unit shown in FIGS. 23 and 24. FIG. 10 is a diagram for explaining an example of gradation conversion operation in gradation conversion means of an image processing apparatus according to Embodiment 4; (A) And (b) is a figure for demonstrating the other example of the operation | movement of the gradation conversion in the gradation conversion means of the image processing apparatus by Embodiment 4. FIG. It is a block diagram which shows roughly an example of a structure of the image display apparatus by Embodiment 5 of this invention. It is a block diagram which shows roughly the other example of a structure of the image display apparatus by Embodiment 6 of this invention.

<< 1 >> Embodiment 1
<< 1-1 >> Overview.
FIG. 1 is a block diagram schematically showing a configuration of an image processing apparatus according to Embodiment 1 of the present invention (that is, an apparatus capable of performing the image processing method according to Embodiment 1). The image processing apparatus according to the first embodiment expands the number of bits (the number of gradations) for converting an m-bit (m is a natural number) digital input image signal Da into an n-bit (n is a natural number) digital output image signal Db. A gradation conversion unit 1 capable of performing gradation conversion processing of (n> m) and a timing signal generation unit 100 that outputs a timing signal Sif that is synchronized with the synchronization signal SY for video display are provided. The gradation conversion processing by the gradation converting means 1 is performed by, for example, expanding the number of bits and adding the correction bit data Cd, which is bit data lower than the input image signal Da, to the m-bit input image signal Da. In this process, the tone value is corrected and an n-bit (n = m + Q) output image signal Db is generated.

  The image processing apparatus according to the first embodiment receives an input image signal Da composed of discrete data in the time direction and the spatial direction, expands the number of gradations of the input image signal Da, and provides gradation values (gradation levels). This is an apparatus for outputting an output image signal Db composed of post-conversion data generated by a conversion process for correcting (level). The gradation conversion means 1 of the image processing apparatus according to the first embodiment includes a gradation change detection means 10, a flat width prediction means 20, an inclination detection means 40, a correction limit coefficient setting means 30, and a correction bit generation means 50. And a delay compensation means 61 and a pixel value calculation means 62. The gradation change detecting means 10 detects, from the input image signal Da, a gradation change amount that is a difference between gradation values of pixels arranged adjacent to each other and a gradation change that is a pixel position where the value of the gradation change amount is not zero. And means for detecting gradation change information (dfx, Xlm, Pt) including the position. The flat width predicting means 20 uses the detected gradation change position pixel as a reference pixel every time a gradation change position pixel is detected from the gradation change information from the gradation change detection means 10. A means for generating a flat width data predicted value dst that is a predicted value of a flat width of a gray level flat section immediately after a reference pixel, wherein the gray level flat section in which pixels of the same gray level immediately before the reference pixel are continuous The flat width data in which the flat width of the gray level flat section immediately after the reference pixel is predicted based on the flat width of the previous pixel and the previous flat width data prediction value generated in the immediately preceding reference pixel detected immediately before the reference pixel. A means for generating a predicted value dst. The inclination detection unit 40 converts the converted data in the gray level flat section immediately after the reference pixel based on the gray level change information from the gray level change detection unit 10 and the flat width data predicted value dst from the flat width prediction unit 20. This is means for obtaining an inclination data value Ksl used when setting the inclination of the gradation value. The correction limiting coefficient setting unit 30 determines whether or not the gradation change at the gradation change position is a gradation change due to the edge of the image based on the gradation change amount dfx from the gradation change detection unit 10. This is means for setting a correction limiting coefficient rc for limiting the gradient of the gradation value of the output image signal Db according to the determination result. The correction bit generation means 50 receives the input image from the gradation change information from the gradation change detection means 10, the inclination data value Ksl from the inclination detection means 40, and the correction restriction coefficient rc from the correction restriction coefficient setting means 30. This is means for obtaining a correction value aCd of the gradation value of the signal Da and generating correction bit data Cd corresponding to the correction value. The delay compensation unit 61 is a unit that delays the input image signal Da and outputs it to the pixel value calculation unit 62 as the image signal Dd. The pixel value calculation means 62 is a means for generating an output image signal Db composed of converted data by subtracting or adding a value corresponding to the correction bit data Cd to the gradation value of the input image signal Da.

  The gradation converting means 1 adds the correction bit data Cd as the lower bits to the m-bit input image signal Da (Dd), thereby converting the m-bit input image signal Da into the n-bit output image signal Db. Expand and output sequentially. Further, the gradation converting means 1 uses the correction limiting coefficient rc so that when the gradation change amount dfx is large (when it is determined that the gradation value change is a change due to the edge of the image), the correction bit is corrected. When the data Cd is set to 0 (or close to 0) and the gradation change amount dfx is small (when it is determined that the gradation value change is a very gradual gradation value change of the image), the correction bit The data Cd is a value based on the inclination data value Ksl. Therefore, by using the image processing apparatus according to the first embodiment, the quantum of the image signal that is likely to be generated in a section in which the gradation value changes very gently in a certain direction (for example, the horizontal direction) of the screen displayed on the screen. The output image signal Db that can display an image with a smoothly changing gradation even in a period where the gradation value of the input image signal Da changes very slowly is generated by reducing the influence of the noise or the pseudo contour can do. In the image processing apparatus according to the first embodiment, when the gradation value changes depending on the edge (contour) of the image, the input image signal is set by setting the correction bit data Cd to 0 (or close to 0). An output image signal Db that is faithful to the value of Da can be generated. For this reason, the display means (not shown in FIG. 1) to which the output image signal Db whose gradation has been converted by the image processing apparatus of the first embodiment is to be displayed faithfully to the value of the input image signal Da. In the contour, the image can be displayed faithfully to the value of the input image signal Da, and in the section where the gradation value of the input image signal Da changes very slowly, the influence of the quantization noise or the pseudo contour is displayed. Display of reduced high-quality images can be realized.

<< 1-2 >> Configuration.
<< 1-2-1 >> Image processing apparatus.
The gradation change detection means 10 in the gradation conversion means 1 is a gradation change that is a change amount of a gradation value between adjacent pixels in a certain direction (for example, the horizontal scanning direction or the vertical scanning direction) of the input image signal Da. The amount dfx is detected, and the gradation change amount dfx, the amplitude limited gradation change amount Xlm obtained from the gradation change amount dfx, and the gradation change position signal Pt obtained from the gradation change amount dfx are output. Means. The flat width predicting means 20 is a period in which the gradation value does not change from a pixel whose gradation value changes based on data sequentially input as the input image signal Da to a pixel immediately before the pixel whose next gradation value changes. A means for obtaining a flat width data predicted value dst obtained by calculating the number of pixels (flat width) of (gradation flat section) and predicting the flat width after the pixel position where the gradation value changes using the obtained flat width. is there. The correction limiting coefficient setting means 30 corrects the correction bit data Cd corresponding to the correction value which is a gradation value to be added to the input image signal Da as a lower bit in order to expand the number of gradations based on the gradation change amount dfx. Is a means for setting a correction limiting coefficient rc used when calculating. The inclination detection means 40 is based on the flat width data predicted value dfx from the flat width prediction means 20 and the amplitude limit gradation change amount Xlm from the floor change amount detection means 10, and the amplitude limit gradation in a fixed direction of the input image signal Da. The value obtained by dividing the change amount Xlm by the flat width data predicted value dfx is assumed to be a gradient data value Ksl (the gradation value is gradually changed gradually by the amplitude limited gradation change amount Xlm within the range of the flat width data predicted value dfx). (Gradient of the gradation value in the case). The correction bit generation means 50 is added as a lower bit to the gradation value of the input pixel signal Da based on the input amplitude limit gradation change amount Xlm, inclination data value Ksl, correction restriction coefficient rc, and timing signal Sif. This is means for generating correction bit data Cd. The delay compensation unit 61 delays the input image signal by a predetermined time corresponding to the time from the input time point of the input image signal Da to the generation time point of the correction bit data Cd by the correction bit generation unit 50, and the input image signal Da. And means for matching the phases of the correction bit data Cd. The pixel value calculation means 62 is a means for outputting the output image signal Db having an expanded number of gradations by adding the correction bit data Cd from the correction bit generation means 50 to the input image signal Da. In the present application, the configuration indicated as “... Means” may be realized by an electric circuit (hardware) or realized by software.

  As shown in FIG. 1, the gradation change amount calculation means 11 in the gradation change detection means 10 is a means for calculating a difference between gradation values (pixel values) between pixels as a gradation change amount dfx. is there. The gradation change amount limiting means 12 outputs a signal in which the gradation change amount dfx is limited so that the gradation change amount dfx falls within a predetermined gradation value range as the amplitude limited gradation change amount Xlm. It is. The gradation change position detecting means 13 is a gradation indicating the position of a pixel having a change in gradation value where the value of the gradation change amount dfx is not 0 and the absolute value of the gradation change amount dfx is greater than 0. This is means for obtaining the change position signal Pt. Note that the gradation change detection means 10 is not limited to the form shown in FIG. 1, and a function for outputting information on the gradation change amount, a function for limiting the amplitude of the gradation change amount, and output gradation change position information. Any other form may be used as long as it has a function to do so.

  As shown in FIG. 1, the flat width predicting unit 20 includes a flat width counting unit 21 and a cyclic filter processing unit 22. The flat width count means 21 is based on the gradation change position signal Pt from the gradation change detection means 10 and the gradation value from the pixel whose gradation value changes to the pixel immediately before the pixel whose gradation value changes next. The flat width is obtained by counting the number of pixels having a flat width corresponding to a flat period in which the same gradation value without any change is continuous (that is, on the screen, a gradation flat section where there is no change in gradation value). A means for outputting a count value Cnt. The recursive filter processing means 22 applies recursive filter processing to the flat width count value Cnt indicating the flat width counted by the flat width count means 21 to flatten the gray level flat section after the pixel at the gray level change position. This is a means for obtaining a flat width data predicted value dst that is a predicted value of the width.

  In FIG. 1, an analog or digital image signal is converted into an m-bit digital image signal format and input to the gradation conversion means 1 as an input image signal Da. The gradation converting means 1 generates, for example, Q-bit corrected bit data Cd and adds it to the least significant side of the m-bit input image signal Da to extend the number of gradations, and the n-bit output image signal Db. Is generated. The bit number m of the input image signal Da is, for example, 8 bits, the bit number Q of the gradation correction value is, for example, 4 bits, and the bit number n of the output image signal Db is, for example, 12 bits. . Further, in the first embodiment, a case will be described in which the fixed direction for detecting the change in the gradation value of the input image signal Da is the horizontal direction of the screen (screen display horizontal scanning direction). Further, in the first embodiment, the gradation converting means 1 has a difference of the least significant 1 bit of the input image signal Da whose gradation change amount dfx is 8 bits, that is, a difference of gradation values between pixels is +1. Alternatively, an interval in which the gradation value changes very slowly as a section where the gradation value changes −1, and gradation conversion processing is performed, and an image in which the gradation changes smoothly in a section where the gradation value changes very slowly. Can be displayed as

  The image signal has a format represented by luminance and chromaticity or a format represented by primary color signals such as red (R), green (G), and blue (B). The image signal processing can be performed for any type of signal. In the following, a case where the gradation converting unit 1 processes any one type of image signal will be described. In the following, image processing is performed in the horizontal direction of the input image signal Da, gradation conversion correction processing for expanding and correcting the number of gradations of the 8-bit input image signal Da, and 12-bit output image signal is performed. A case of outputting as Db will be described.

  In FIG. 1, a timing signal generation unit 100 receives a synchronization signal SY for an input image signal Da and generates a timing signal based on the synchronization signal SY. When the gradation conversion unit 1 performs image processing in the horizontal direction of the input image signal Da, the timing signal generation unit 100 uses, for example, each process in the gradation conversion unit 1 as a timing signal in the horizontal direction. An initialization signal Sif for initialization is generated for each signal (horizontal synchronization signal). Therefore, the initialization signal Sif may be generated as a pulse signal indicating the start timing of the horizontal scanning period with reference to the horizontal synchronization signal, for example.

  The gradation conversion unit 1 receives the input image signal Da and the initialization signal Sif from the timing signal generation unit 100. The gradation conversion means 1 performs gradation conversion for expanding the number of bits by adding, for example, 4-bit correction bit data Cd to the 8-bit input image signal Da, and outputs a 12-bit output image signal Db. Output as. The gradation converting means 1 obtains the gradation change amount dfx from the difference in gradation value between adjacent pixels of the input image signal Da, and flattenes the gradation flat section up to the pixel immediately before the pixel at the gradation change position. From the width, a flat width data predicted value dst obtained by predicting the flat width of the gradation flat section after the pixel immediately after the pixel at the gradation change position is obtained, and the amplitude limited gradation change amount Xlm based on the gradation change amount dfx is obtained. The slope data value Ksl is calculated from the flat width data predicted value dst and the corrected bit data Cd is generated using the slope data value Ksl. The gradation converting means 1 extends the number of bits of the input image signal Da by adding correction bit data Cd as lower bits to the input image signal Da. By such processing, the gradation converting means 1 detects a minute gradation value change in a section where the gradation value changes very gently, and the gradation of the image signal is changed to a sufficient number of gradations. It is expanded and output as a high-quality 12-bit output image signal Db having a smooth gradation value change.

  2A to 2C are diagrams showing signal waveforms (when the gradation value of the input image signal Da increases very slowly) in the image processing apparatus according to the first embodiment, and FIG. ) Indicates the gradation value La (x) (range of gradation values 1 to 8) near the least significant bit of the 8-bit input image signal Da, and FIG. 2B shows the gradation value of the input image signal Da. The change amount dfx and the gradation change positions Pt (8), Pt (16),... Are shown, and FIG. 2 (c) shows the levels in the vicinity of the least significant bit of the 12-bit output image signal Db with the expanded number of gradations. The tone value Lb (x) (range of tone values 16 to 128) is indicated. 2A to 2C indicate the positions x of pixels arranged in the horizontal direction of the screen. Also, the vertical axis in FIG. 2A indicates the gradation value La (x) of the 8-bit input image signal Da at each pixel position, and the vertical axis in FIG. 2B indicates the gradation change amount dfx. In FIG. 2C, the vertical axis indicates the gradation value Lb (x) of the 12-bit output image signal Db at each pixel position. In FIG. 2A, the gradation value La (x) of the input image signal Da gradually increases by one gradation corresponding to the least significant 1 bit of the gradation value every 8 pixels at the horizontal pixel position. The case is shown. FIG. 2B shows the relationship between the gradation change amount dfx of the input image signal Da obtained by the gradation conversion means 1, the flat width of the gradation flat section where the gradation value does not change, and the pixel position. ing. FIG. 2C shows a change in the gradation value Lb (x) of the 12-bit output image signal Db output from the gradation converting means 1.

  FIGS. 3A to 3C are diagrams showing signal waveforms (when the gradation value of the input image signal Da decreases very slowly) in the image processing apparatus according to the first embodiment, and FIG. ) Indicates the gradation value La (x) (range of gradation values 1 to 8) near the least significant bit of the 8-bit input image signal Da, and FIG. 3B shows the gradation value of the input image signal Da. The change amount dfx and the gradation change positions Pt (8), Pt (16),... Are shown, and FIG. 3 (c) shows the steps in the vicinity of the least significant bit of the 12-bit output image signal Db with the expanded number of gradations. The tone value Lb (x) (range of tone values 16 to 128) is indicated. Note that the horizontal axis of FIGS. 3A to 3C indicates the position x of the pixels arranged in the horizontal direction of the screen. Also, the vertical axis in FIG. 3A indicates the gradation value La (x) of the 8-bit input image signal Da at each pixel position, and the vertical axis in FIG. 3B indicates the gradation change amount dfx. In FIG. 3C, the vertical axis indicates the gradation value Lb (x) of the 12-bit output image signal Db at each pixel position. In FIG. 3 (a), the gradation value La (x) of the input image signal Da gradually decreases by 1 gradation corresponding to the least significant 1 bit of the gradation value every 8 pixels at the pixel position in the horizontal direction. The case is shown. FIG. 3B shows the relationship between the gradation change amount dfx of the input image signal Da obtained by the gradation converting means 1, the flat width of the gradation flat section where the gradation value does not change, and the pixel position. ing. FIG. 3C shows a change in the gradation value Lb (x) of the 12-bit output image signal Db output from the gradation converting means 1.

  FIG. 2A shows the case where the input image signal Da changes (increases) by one gradation and gradation value every 8 pixels in the range where the horizontal pixel position x is from 8 to 56. FIG. Has been. FIG. 3A shows a case where the input image signal Da changes (decreases) in gradation value by 1 gradation every 8 pixels within the horizontal pixel position x in the range from 16 to 56. FIG. Has been. In the first embodiment, if the difference between the gradation values is two or more gradations (for example, the gradation value when the pixel position x = 7 and the gradation value when x = 8 in FIG. 3A). ), The signal gradation value is not changed very slowly at the boundary between adjacent pixels (that is, the gradation change due to the edge of the image). There is no problem even if it is displayed. On the other hand, when the gradation value difference is 1 gradation, the gradation value of the signal changes very slowly at the boundary between adjacent pixels, but quantization noise or pseudo contour occurs near the boundary. There is a case. In this way, the gradation of the display image changes more smoothly in the interval in which the gradation value changes very gently, with the gradation value difference being one gradation (for example, FIG. 2C). Therefore, as shown in FIG. 3C, the image processing apparatus according to the first embodiment performs gradation conversion by increasing the number of gradations of the input image signal Da to obtain the output image signal Db.

  Hereinafter, the configuration in the gradation converting means 1 will be described in detail with reference to FIGS. 1, 2A to 2C, and FIGS. 3A to 3C.

<< 1-2-2 >> Gradation change detecting means
An input image signal Da is input to the gradation change detection means 10. The gradation change detection means 10 calculates a difference in gradation value (pixel value or gradation level) between pixels adjacent in the horizontal direction in the input image signal Da, obtains it as a gradation change amount dfx, and outputs this. . Further, the gradation change detecting means 10 is an amplitude-limited gradation change amount Xlm in which the value of the gradation change amount dfx is limited within a predetermined range, and a pixel whose gradation value has changed from the value of the gradation change amount dfx. A gradation change position signal Pt having a value corresponding to whether or not and including information on a pixel position where the gradation value has changed is output.

  When the input image signal Da as shown in FIG. 2A or FIG. 3A is input to the gradation change detection means 10, the gradation change detection means 10 detects the horizontal pixel position x and immediately before it. By calculating the difference in gradation value between the pixels (pixel position x−1), for example, the gradation change amount dfx as shown in FIG. 2B or FIG. Pixels for which the obtained gradation change amount dfx is not 0 are detected as the positions of the pixels whose gradation values change. In the example of FIG. 2B, the gradation change position of the gradation change amount dfx = + 1 is detected from the pixel position x = 8 to every eight pixel positions, and the pixels between the gradation change positions are detected. A gradation change amount dfx = 0 is detected. In the example of FIG. 3B, the gradation change position of the gradation change amount dfx = + 7 is detected at the pixel position x = 8, and the gradation change amount is detected from the pixel position x = 16 at every pixel position. A gradation change position of dfx = −1 is detected, and a gradation change amount dfx = 0 is detected in pixels between the gradation change positions.

  The gradation change detection means 10 includes, for example, a gradation change amount calculation means 11, a gradation change amount restriction means 12, and a gradation change position detection means 13. The gradation change amount calculation means 11 calculates, for example, a gradation change amount dfx that is a difference in gradation value between images adjacent in the horizontal direction from the input image signal Da, and calculates the calculated gradation change amount dfx. Is output to the gradation change amount limiting means 12, the gradation change position detecting means 13, and the correction limiting coefficient setting means 30. The gradation change amount limiting unit 12 outputs the amplitude limit gradation change amount Xlm generated based on the gradation change amount dfx to the inclination detection unit 40 and the correction bit generation unit 50. The gradation change position detection means 13 outputs the gradation change position signal Pt obtained based on the gradation change amount dfx to the flat width prediction means 20, the inclination detection means 40, and the correction bit generation means 50.

When the input image signal Da is input to the gradation change amount calculation unit 11, the gradation change amount calculation unit 11 calculates a difference in gradation values between pixels adjacent in the horizontal direction in the input image signal Da. It is obtained as a tone change amount dfx. Here, assuming that the horizontal pixel position of the pixel of interest to be processed is x and the gradation value at this pixel position is L (a), the gradation change amount calculation means 11 is the pixel immediately before the pixel of interest position x (pixel position). When the gradation value obtained by delaying x-1) by one pixel is La (x-1), the gradation value La (x) at the pixel position x-1 is changed from the gradation value L (a) at the pixel position x. The gradation change amount dfx is obtained by calculating a value obtained by subtracting -1). That is, according to FIG. 2 (a) or FIG. 3 (a), the gradation change amount dfx, which is the difference in gradation values between pixels, is
dfx = La (x) −La (x−1)
Can be calculated with When the gradation change amount dfx, which is the difference in gradation value between pixels, is 0, the pixel is in a gradation flat section where there is no change in gradation value, and in the pixel where the gradation value has changed, the absolute value of the difference Is the difference between the gradation values, and the direction of the increase or decrease in the gradation value is obtained as a sign of the value (a positive sign “+” when the gradation is increased, a negative sign “−” when the gradation is decreased). It is done.

  When the gradation change amount dfx from the gradation change amount calculation means 11 is input to the gradation change amount restriction means 12, the gradation change amount restriction means 12 causes the gradation change amount dfx to fall within a predetermined gradation value range. In other words, the value is limited to a value (integer) within a range from −1 to +1, and the gradation change amount with the limited value is output as the amplitude limited gradation change amount Xlm. The range from −1 to +1, which is the limit range here, detects a change in one gradation value, which is the difference of the least significant 1 bit of the 8-bit input image signal Da in the gradation converting means 1. Because. Therefore, the amplitude limit gradation change amount Xlm output from the gradation change amount limiting means 12 is composed of three values of −1, 0, and +1.

  When the gradation change amount dfx from the gradation change amount calculation means 11 is input to the gradation change position detection means 13, the gradation change position detection means 13 determines the gradation value from the value of the gradation change amount dfx. The position of the changing pixel is detected, and a gradation change position signal Pt with a binarized value is output as the detection result. For example, the gradation change position detecting means 13 has a change in gradation value if the absolute value of the gradation change amount dfx is greater than 0, that is, a difference of 1 gradation or more. On the other hand, if the gradation change amount dfx is 0, the pixel is determined to be flat without changing the gradation value. Then, the gradation change position detection unit 13 outputs a gradation change position signal Pt indicating a binarized value as a detection result. The value of the gradation change position signal Pt is, for example, the value “1” (Pt = 1) at the pixel position where the gradation change amount dfx ≠ 0 determined that the gradation value has changed, and the gradation value changes. A value of “0” (Pt = 0) is set for a pixel having a gray level change amount dfx = 0. Note that the value of the gradation change position signal Pt is not limited to the above value, and may be another value as long as the position of the pixel where the gradation value changes is indicated. Further, the value of the gradation change position signal Pt is the same as the value of the gradation change amount dfx itself or the amplitude-limited gradation change amount Xlm by the gradation change amount limiting means 12, and the value is limited to a predetermined range. Any signal can be used as long as it can determine whether a pixel has a change in gradation value.

<< 1-2-3 >> Flat width prediction means 20.
The flat width predicting means 20 receives the gradation change position signal Pt from the gradation change position detecting means 13 and the initialization signal Sif from the timing signal generating means 100. The flat width predicting unit 20 initializes each process for each horizontal scanning period by the initialization signal Sif, and determines the pixel (reference pixel) position indicated by the gradation change position signal Pt from the gradation change position detection unit 13. For each pixel (reference pixel) position where the gradation value for which the gradation change position signal Pt = 1 is changed, the number of pixels (flat width) in the gradation flat section up to the pixel immediately before the reference pixel is determined as a reference. A flat width data predicted value dst that is a predicted value of the flat width of the gray level flat section after the pixel immediately after the pixel having the gray level change position signal Pt = 1 is obtained. The flat width prediction unit 20 outputs the obtained flat width data prediction value dst to the inclination detection unit 40. The flat width data predicted value dst is used as the horizontal width when the inclination detecting unit 40 calculates the inclination of the gradation value in the horizontal direction (= change amount of gradation value / horizontal width).

  FIG. 4 is a block diagram schematically showing an example of the configuration of the flat width predicting means 20. The flat width predicting means 20 obtains the number of pixels in a period (gradation flat section) in which the gradation value does not change in the horizontal direction of the screen and the gradation value is flat, and for each pixel position where the gradation value changes, A flat width data predicted value dst obtained by predicting the flat width after the position is obtained. As shown in FIG. 4, the flat width predicting unit 20 includes a flat width counting unit 21 and a cyclic filter processing unit 22. The flat width counting unit 21 includes, for example, a pixel counting unit 23 and a delay unit 24 that delays the count value for one pixel. The cyclic filter processing means 22 includes, for example, a coefficient 1 multiplication means 25, a coefficient 2 multiplication means 27, a calculation means 26, a switching means 28, and a filter output delay means 29.

  The flat width count means 21 receives the gradation change position signal Pt from the gradation change position detection means 13 in the gradation change detection means 10 and the initialization signal Sif from the timing signal generation means 100. The flat width count unit 21 initializes the count value by the initialization signal Sif, for example, every horizontal scanning period (sets the count value to 0), and changes the gradation change position from the gradation change position detection unit 13. Using the position of the pixel (reference pixel) indicated by the signal Pt as a reference, the number of pixels in the gradation flat section up to the pixel immediately before the reference pixel is counted, and a flat width count value Cnt that is the number of pixels is output.

  Specifically, first, the pixel count means 23 in the flat width count means 21 includes a gradation change position signal Pt, an initialization signal Sif, and a pixel one pixel before by the delay means 24 in the flat width count means 21. The flat width count value Cnt at is input. The pixel counting means 23 counts the number of pixels in the horizontal direction with reference to the gradation change position signal Pt and the initialization signal Sif, and obtains a pixel count value Cnt0 corresponding to the flat width value of the gradation flat section. That is, the pixel count unit 23 initializes the count value for each horizontal scanning period by the initialization signal Sif (sets the pixel count value Cnt0 = 0) and is indicated by Pt = 1 by the gradation change position signal Pt. At the pixel position where the gradation value changes, the count value is reset to “0” (pixel count value Cnt0 = 0). In other cases, the pixel counting unit 23 adds 1 to the flat width count value Cnt of the pixel one pixel before the delay unit 24, that is, the count value of the immediately preceding pixel, and counts the number of pixels. Since the gradation change position signal Pt is obtained from a value based on the gradation change amount dfx and indicates the pixel position where the gradation value changes, the pixel counting means 23 uses the pixel where the gradation change amount dfx = 0. The number of consecutive pixels (the number of consecutive pixels that become 0), that is, the number of pixels in the gradation flat section in which the gradation value has not changed can be acquired.

  The delay means 24 in the flat width count means 21 delays and outputs a pixel count value Cnt0 indicating the flat width by the pixel count means 23 by one pixel. As a result, the delay unit 24 outputs a flat width count value Cnt of a flat width up to the pixel immediately before the target pixel position, and at the pixel position where the gradation value changes with the gradation change position signal Pt = 1, (A continuous width of pixels where the gradation change amount dfx = 0).

  For example, when the gradation change amount dfx and the gradation change position signal Pt shown in FIGS. 2B and 3B are obtained, the pixel position (pixel position x) of the gradation change amount dfx ≠ 0 is obtained. = 16, 24, 32, 40, 48, 57) The flat width up to the previous pixel is obtained as the flat width count value Cnt. In the example of FIG. 2B, at the pixel position x = 16 where the gradation value changes, the number of pixels (Cnt = 7) from the pixel position x = 9 to x = 15 is obtained as the flat width.

  As described above, the flat width in the horizontal direction up to the immediately preceding pixel at the pixel position where the gradation value changes is obtained as the flat width count value Cnt from the flat width count means 21, and this flat width count value Cnt is the cyclic filter. It is output to the processing means 22.

  Next, the cyclic filter processing unit 22 in the flat width prediction unit 20 also receives the gradation change position signal Pt from the gradation change position detection unit 13 in the gradation change detection unit 10 and the timing signal generation unit 100. The flat width count value Cnt from the delay means 24 in the flat width count means 21 is further input to the cyclic filter processing means 22. The recursive filter processing means 22 initializes the output result for each horizontal scanning period by the initialization signal Sif (value is set to “0”), and the gradation value indicated by the gradation change position signal Pt = 1 is obtained. The flat width count value Cnt at the changing pixel position is subjected to cyclic filter processing for each gradation change position signal Pt = 1, and the result of this filter processing is the flat width after the pixel position where the gradation value changes. Is output as a flat width data predicted value dst which is a predicted value. The recursive filter processing means 22 is a low-pass filter (also referred to as “LPF”), and is a recursive filter (“IIR (Infinite Impulse Response) filter”) based on an input signal and a filter output delayed by the filter output delay means 29. It is also said.) The IIR filter uses a smaller number of delay means (memory) than the configuration of an acyclic filter (also referred to as “FIR (Finite Impulse Response) filter”) based on signals of several adjacent pixels of the input signal. It can be constant regardless of the pixel range to be filtered.

In FIG. 4, the coefficient 1 multiplication means 25 and the coefficient 2 multiplication means 27 in the cyclic filter processing means 22 are set with predetermined filter coefficients, and perform an operation of multiplying each input signal by a filter coefficient. Here, when the filter coefficient of the coefficient 1 multiplication means 25 is k ₁ and the filter coefficient of the coefficient 2 multiplication means 27 is k ₂ , k ₁ = 1−k ₂ , 0 ≦ k ₁ ≦ 1, 0 ≦ k ₂ ≦ By setting the values of the filter coefficients k ₁ and k ₂ , the size of the past output value to be circulated, that is, the range of the region affected by the obtained flat width is determined.

When the flat width count value Cnt from the delay means 24 of the coefficients within a multiplying means 25 to a flat width counting means 21 is inputted, the coefficient 1 multiplying means 25 multiplies the filter coefficients k ₁ to a flat width count value Cnt , The multiplication result (Cnt) × (k ₁ ) is output. The coefficient 2 multiplying unit 27 includes a delay flat width data predicted value pdst (that is, a level before the current pixel position) that is a filter processing output at the immediately previous pixel position delayed by one pixel by a filter output delay unit 29 described later. The result of the filtering process on the pixel whose tone value has changed is input. The coefficient 2 multiplication unit 27 multiplies the delay flat width data predicted value pdst by the filter coefficient k ₂ and outputs a multiplication result (pdst) × (k ₂ ).

The calculation means 26 in the recursive filter processing means 22 includes a coefficient multiplication result (Cnt) × (k ₁ ) generated by the coefficient 1 multiplication means 25 based on the flat width count value Cnt, and the delayed flat width data predicted value pdst. The coefficient multiplication result (pdst) × (k ₂ ) generated by the coefficient 2 multiplication means 27 based on the above is input. The computing unit 26 adds the input coefficient multiplication result (Cnt) × (k ₁ ) and (pdst) × (k ₂ ), and outputs the addition result as the filter processing result fdst. Since the delay flat width data predicted value pdst is a filter processing output at the pixel position immediately before being delayed by one pixel by the filter output delay unit 29, the coefficient 1 multiplication unit 25, the coefficient 2 multiplication unit 27, and the calculation unit 26 The calculation corresponds to cyclic filter processing, and is an operation represented by the following equation (1).
fdst
= K ₂ × pdst + k ₁ × Cnt
= K ₂ × pdst + (1−k ₂ ) × Cnt Equation (1)

  Further, the calculation of the cyclic filter processing according to the above equation (1) corresponds to the processing of the low-pass filter, and the low-frequency component having a flat width when the gradation value changes in the horizontal direction, that is, Smoothed continuity is obtained, and it is possible to avoid detecting a sudden change in gradation value as a flat width.

  The switching means 28 in the cyclic filter processing means 22 includes a gradation change position signal Pt, an initialization signal Sif, a filter processing result fdst from the calculation means 26, and a delay flat width data from the filter output delay means 29. The predicted value pdst is input. The switching means 28 responds to the initialization signal Sif and the gradation change position signal Pt, the filter processing result fdst from the computing means 26, the delay flat width data predicted value pdst from the filter output delay means 29, and the initialization value. One of “0” is selected, and the selected value is output as a flat width data predicted value dst that is a predicted value of the flat width of the gradation flat section after the pixel position where the gradation value changes.

  That is, the switching means 28 selects the initialization value “0” when the input initialization signal Sif indicates initialization at the boundary of the horizontal scanning period, and sets the value “0” as the flat width data predicted value dst. '(Ie, dst = 0) is output. Then, the switching means 28 is an arithmetic means that is a result of performing cyclic filter processing on the flat width count value Cnt at the pixel position (Pt = 1) where the gradation value changes according to the gradation change position signal Pt. The filter processing result fdst from 26 is selected, and the selected filter processing result fdst is output as the flat width data predicted value dst. On the other hand, the switching means 28 has the delay flat width data predicted value pdst (that is, the gradation value before the current pixel position) from the filter output delay means 29 changed in the gradation flat section (Pt = 0 section). Corresponding to the filter processing result fdst in the pixel), and the selected delayed flat width data predicted value pdst is output as the flat width data predicted value dst.

  As a result, a result obtained by performing the cyclic filter process on the flat width count value Cnt at each pixel position (Pt = 1) where the gradation value changes is obtained as the flat width data predicted value dst. In the tone flat section, the value of the pixel whose gradation value has changed before that is held and output.

  The flat width data predicted value dst from the switching unit 28 is output to the inclination detecting unit 40 as an output from the cyclic filter processing unit 22 and also sent to the filter output delay unit 29 in the cyclic filter processing unit 22.

  The filter output delay means 29 delays the flat width data predicted value dst from the switching means 28 by one pixel, and outputs the flat width data predicted value dst delayed by one pixel as the delayed flat width data predicted value pdst. The filter output delay means 29 delays the flat width data predicted value dst output from the switching means 28 by one pixel, so that the flat width data predicted value dst at the immediately preceding pixel is output as it is as the delayed flat width data predicted value pdst. The result of the cyclic filter processing (flat width data predicted value dst) for the flat width count value Cnt is held until the pixel position where the gradation value changes next for each pixel whose gradation value changes. Is done.

  As a result of the above processing, the cyclic filter processing unit 22 changes the gradation value with respect to the flat width count value Cnt at the pixel position where the gradation value indicated by the gradation change position signal Pt = 1 changes. The flat width data prediction value dst that has been subjected to the cyclic filter processing for each position is output. The flat width data predicted value dst is obtained by performing cyclic low-pass filter processing using the filter processing output delayed by the filter output delay means 29 on the flat width count value Cnt at the pixel position where the gradation value changes. It is obtained as a low-frequency component of the flat width when the gradation value changes in the horizontal direction, that is, a flat width value indicating smoothed continuity. Therefore, in the pixel region where the gradation value changes gradually in the horizontal direction, the flat width of the gradation flat section when the gradation value changes can be generated so as not to change sharply. . Thus, the flat width data predicted value dst can be used as a value predicting the flat width of the change in the gradation value after the pixel position where the gradation value indicated by the gradation change position signal Pt = 1 changes. .

  Further, since the processing in the cyclic filter processing means 22 is cyclic, the result of the filter processing is obtained as a flat width data predicted value dst that is a predicted flat width after the pixel position where the gradation value changes. The delay means (that is, the memory) to be used is a delay means 24 having a size corresponding to the pixel count value in the flat width count means 21 and a one-pixel delay memory in the filter output delay means 29 in the cyclic filter processing means 22. The number of memories corresponding to the flat width to be detected is not required. For this reason, a 1-pixel delay memory may be used regardless of the pixel range corresponding to the detected flat width, and flat width data prediction that is a value predicting the flat width even in a period where the gradation value changes very slowly. The value dst is obtained, and the width of the gray level flat section in which the gray level value does not change can be obtained without significantly increasing the circuit scale. For example, even when the pixel count value Cnt in the flat width count means 21 is counted up to 1023 pixels (10 bits), both the delay means 24 and the filter output delay means 29 are 10-bit 1-pixel delay memories. It is possible to obtain a flat width data prediction value dst up to 1023 pixel widths only by having it.

<< 1-2-4 >> Correction limit coefficient setting means 30.
Next, the correction limiting coefficient setting means 30 will be described in detail with reference to FIG. The correction limit coefficient setting means 30 receives the gradation change amount dfx from the gradation change amount calculation means 11 in the gradation change detection means 10. The correction limit coefficient setting means 30 is a correction limit coefficient rc used to limit the correction value when the correction bit generation means 50 generates a correction value (correction bit data Cd) for the expansion of the number of gradations. And the correction limit coefficient rc is output to the correction bit generation means 50.

  Here, the gradation change amount dfx from the gradation change detection means 10 is calculated from the difference in gradation value between adjacent pixels, and in the pixels adjacent to the edge of the image (for example, the contour of the image), It also includes the difference in gradation value due to the edge component of the image. In the first embodiment, an area of a pixel whose number of gradations is expanded by the gradation converting unit 1 is an area in which the difference in gradation values is a change corresponding to the least significant 1 bit of the input image signal Da (very smooth). The area in which the gradation value changes). For this reason, it is necessary to prevent the correction value from being added to the gradation value at the edge of the image. Therefore, the correction limiting coefficient setting unit 30 determines whether the change in the gradation value (that is, the difference in the gradation value) is due to the edge of the image based on the magnitude of the gradation change amount dfx. From this result, the correction limiting coefficient rc is set as a value that can limit the correction value so that the gradation correction value is not added to the edge of the image.

  FIG. 5 is a block diagram schematically showing an example of the configuration of the correction limiting coefficient setting unit 30. As shown in FIG. In FIG. 5, the correction limiting coefficient setting means 30 calculates the correction limiting coefficient based on, for example, the magnitude of the absolute value of the gradation change amount dfx and the magnitude of the low frequency component (low frequency component) of the gradation change amount dfx. A configuration for setting rc is shown. The correction limiting coefficient setting means 30 uses the low-frequency component of the gradation change amount dfx, not only the gradation change amount dfx, so that the gradation due to the edge of the image in the pixel near the pixel position where the gradation value changes. A change in the tone value can be taken into consideration, and it can be determined whether or not the pixel has an edge of the image with higher accuracy.

  As shown in FIG. 5, the correction limiting coefficient setting means 30 includes, for example, an absolute value calculation means 31, a differential low frequency component extraction means 32, an absolute value calculation means 33, a magnification conversion means 34, and a maximum value selection. It comprises means 35 and coefficient conversion means 36.

  When the gradation change amount dfx is input to the absolute value calculation means 31 in the correction limiting coefficient setting means 30, the absolute value calculation means 31 calculates the absolute value of the gradation change amount dfx, and the gradation change amount is obtained as the calculation result. The absolute value dxc is output.

  When the gradation change amount dfx from the gradation change amount calculation means 11 is input to the difference low-frequency component extraction means 32, the difference low-frequency component extraction means 32 performs a horizontal LPF (horizontal) with respect to the gradation change amount dfx. LPF) processing is performed to smooth the gradation change amount dfx, thereby extracting and outputting a low frequency component (referred to as “differential low frequency component”) dflp of the gradation change amount dfx. When considering the memory capacity, the differential low-frequency component extraction means 32 can be reduced in circuit scale if it is constituted by an IIR filter that performs filter processing by circulating the filter output. Further, the differential low-frequency component extracting unit 32 may use a value obtained by adding the gradation change amount dfx between adjacent pixels.

  When the differential low-frequency component dflp from the differential low-frequency component extracting means 32 is input to the absolute value calculating means 33, the absolute value calculating means 33 calculates the absolute value of the differential low-frequency component dflp and outputs the difference low as the calculation result. The band component absolute value abslp is output.

  When the differential low frequency component absolute value abslp from the absolute value calculation means 33 is input to the magnification conversion means 34, the magnification conversion means 34 applies a predetermined magnification to the differential low frequency component absolute value abslp from the absolute value calculation means 33. Multiplication is performed to perform gain adjustment (that is, conversion processing of the differential low-frequency component absolute value abslp), and the magnification conversion differential low-frequency component dxlpf obtained by the conversion processing is output to the maximum value selection unit 35. The difference low-frequency component absolute value abslp is a value obtained as an absolute value of the result of extracting the low-frequency component of the gradation change amount fx by the differential low-frequency component extraction means 32 (that is, the differential low-frequency component dflp). The gradation value is different from the gradation change amount absolute value dxc from the absolute value calculation means 31 that has not undergone the low-frequency component extraction processing by the differential low-frequency component extraction means 32. The magnification conversion unit 34 adjusts the gain of the difference low-frequency component absolute value abslp from the absolute value calculation unit 33 and converts it into a magnification conversion difference low-frequency component dxlpf, thereby converting the gradation value of the magnification conversion difference low-frequency component dxlpf. Then, the gradation value is adjusted to a gradation value corresponding to the gradation value of the gradation change amount absolute value dxc from the absolute value calculation means 31. Note that by changing the gain adjustment magnification in the magnification conversion means 34, it is possible to adjust the detection sensitivity of the edge of the image in determining whether the difference in gradation is a difference in gradation due to the edge of the image. it can.

  When the gradation change amount absolute value dxc from the absolute value calculator 31 and the magnification conversion difference low-frequency component dxlpf from the magnification converter 34 are input to the maximum value selector 35, the maximum value selector 35 is input. The gradation change amount absolute value dxc and the magnification conversion difference low-frequency component dxlpf are compared, the maximum value among these values is selected, and the selected maximum value is output as the maximum difference absolute value dfm. That is, the maximum difference absolute value dfm indicates the difference between the edge of the image in the horizontal direction or the gradation value in the vicinity of the target pixel, and therefore the presence / absence of the edge of the image is determined from the magnitude of the difference between the gradation values. Can be determined. The maximum difference absolute value dfm from the maximum value selection unit 35 is output to the coefficient conversion unit 36.

  When the maximum difference absolute value dfm from the maximum value selection unit 35 is input to the coefficient conversion unit 36, the coefficient conversion unit 36 changes the gradation value from the value of the maximum difference absolute value dfm from the maximum value selection unit 35. Is a signal that can limit the generated correction value so that the correction value of the gradation is not added to the input image signal Da at the edge of the image. The correction limit coefficient rc is set, and the set correction limit coefficient rc is output to the correction bit generation means 50.

  Here, the correction limiting coefficient rc set by the correction limiting coefficient setting means 30 is a multiplication value for the gradation correction value, and is set as a value in the range from 0 to 1. Since the correction limiting coefficient rc is a multiplication value for the gradation correction value, if the correction limiting coefficient rc is 0, the correction value is also 0. In addition, in the pixel region where the gradation value changes smoothly and the number of gradations is expanded, the correction restriction coefficient setting unit 30 adds correction bit data based on the correction value to the value of the image signal. The correction limiting coefficient rc is set to 1.

The coefficient conversion unit 36 calculates the value of the correction limiting coefficient rc according to the value of the maximum difference absolute value dfm from the maximum value selection unit 35. For example, the coefficient conversion unit 36 compares the maximum difference absolute value dfm with a predetermined value TH, and if the maximum difference absolute value dfm is equal to or less than the predetermined value TH, the correction limiting coefficient rc is set to 1, and the maximum When the difference absolute value dfm is between the value TH and twice the value TH (2 × TH), the value of rc is changed so that the correction limiting coefficient rc approaches 0 as the maximum difference absolute value dfm increases. For example, it calculates as a value like the following formula (2).
rc = (2 × TH−dfm) / TH (2)
When the maximum difference absolute value dfm is 2 × TH or more, the correction limiting coefficient rc is set to 0. In this case, it is determined that the change in the gradation value is due to the edge of the image.

  The predetermined value TH to be compared is a difference of the least significant 1 bit of the input image signal Da, that is, an absolute value of +1 and −1 which is a difference in gradation value between pixels, and 1 do it.

  With the above configuration, the correction limiting coefficient rc that varies within the range from 0 to 1 according to the value of the maximum difference absolute value dfm is obtained, the maximum difference absolute value dfm is small (TH = 1 or less), and the level is smooth. In the pixel region where the tone value changes, the correction limiting coefficient rc = 1, the maximum difference absolute value dfm is large, and when it is determined that the gradation difference is caused by the edge of the image, the correction limiting coefficient rc is 0, or The correction limiting coefficient rc can be obtained as a value that can limit the correction value so that the correction value of the gradation is not added at the edge of the image.

  FIG. 6 is a diagram showing characteristics of conversion to the correction limiting coefficient rc (vertical axis) with respect to the maximum difference absolute value dfm (horizontal axis) in the coefficient conversion means 36. FIG. 6 shows a case where the coefficient conversion means 36 outputs the correction limiting coefficient rc as a value within the range from 0 to 1. When the maximum difference absolute value dfm increases, the value of the correction limiting coefficient rc approaches 0, and it is determined that the change in gradation value is due to the edge of the image, and the correction value is limited so that the number of gradations is not expanded. On the other hand, when the value of the maximum difference absolute value dfm is equal to or less than the threshold value TH = 1, the correction limiting coefficient rc = 1, which is a gradual change in gradation value that is a difference between +1 and −1. Set to do number expansion. As a result, the correction limit coefficient rc is set to rc = 0 for a pixel that is determined to have an image edge near the pixel whose gradation value changes, and the correction value is limited by the value. Become.

FIGS. 7A and 7B are diagrams illustrating an example of a change in gradation value at which the correction limit coefficient rc set by the correction limit coefficient setting unit 30 is zero. 7A and 7B, the horizontal axis represents the pixel position in the horizontal direction, and the vertical axis represents the gradation value La (x) of the input image signal Da at each pixel position. For example, in the case shown in FIG. 7A, the absolute value of the gradation change amount dfx at the pixel position x ₀ where the gradation value changes, that is, the maximum difference absolute value dfm becomes larger than the threshold value TH = 1. , the value of the correction limiting coefficient rc at the pixel position x ₀ is 0, the change in the gradation value is determined to be due to the edge of the image. In the case shown in FIG. 7 (b), the gradation variation dfx = 3 becomes the pixel position x ₀ +1 adjacent to the pixel position x ₀ of the gradation value changes, a difference low-frequency component shown in FIG. 5 When dflp is a value based on the horizontal LPF with the left and right pixels, the maximum difference absolute value dfm becomes larger than the threshold value TH = 1, the value of the correction limiting coefficient rc approaches 0, and the change in the gradation value is the edge of the image. It is judged that. Then, from the value of the correction limiting coefficient rc at the pixel position x ₀ and subsequent pixels in FIGS. 7 (a) and (b), the correction value is limited.

  Although the case where the coefficient conversion unit 36 sets the correction limiting coefficient rc from the comparison with the predetermined value TH and the calculation according to the equation (2) has been described, the ROM (Read Only Memory) is based on the maximum difference absolute value dfm. ) Or the like, the correction limiting coefficient rc may be set by conversion obtained in advance, for example, as shown in FIG. Further, the maximum difference absolute value dfm may be a fixed value within a range from 0 to 1 even for a value between the value TH and a value twice the value TH (2 × TH). Furthermore, the value of the correction limit coefficient rc may be a binary signal of 0 and 1. The correction limit coefficient rc indicates the correction value of a pixel determined to have an image edge near the pixel where the gradation value changes. Any value that can be limited is acceptable.

  As described above, the correction limiting coefficient setting unit 30 in FIG. 5 obtains the correction limiting coefficient rc that changes according to the magnitude of the gradation change amount dfx as a value within the range from 0 to 1. Output to the correction bit generation means 50.

<< 1-2-5 >> Tilt detection means 40.
The inclination detection means 40 includes a gradation change position signal Pt from the gradation change position detection means 13 in the gradation change detection means 10, an amplitude limit gradation change amount Xlm from the gradation change amount restriction means 12, and The flat width data predicted value dst from the cyclic filter processing means 22 in the flat width prediction means 20 is input. The inclination detection means 40 detects the horizontal direction of the input image signal Da from the amplitude limit gradation change amount Xlm and the flat width data predicted value dst at the pixel position where the gradation value indicated by the gradation change position signal Pt = 1 changes. The gradient data value Ksl is detected, and the obtained gradient data value Ksl is output to the correction bit generation means 50. Since the amplitude limit gradation change amount Xlm is input as a value in which the gradation change amount dfx is limited within a range from −1 to +1, the gradient of the detected gradation value ranges from −1 to +1. It becomes the value in.

  FIG. 8 is a block diagram schematically showing an example of the configuration of the inclination detecting means 40. As shown in FIG. 8, the inclination detection means 40 includes, for example, an inclination calculation means 41, a switching means 42, and an inclination delay means 43.

In FIG. 8, the gradient calculating unit 41 receives the amplitude limited gradation change amount Xlm from the gradation change amount limiting unit 12 and the flat width data predicted value dst from the flat width predicting unit 20. The inclination calculation means 41 calculates a fine inclination divk of the gradation value from the value of the amplitude limit gradation change amount Xlm and the flat width data predicted value dst by the following equation (3).
divk = Xlm / dst (3)

  The amplitude limit gradation change amount Xlm is limited within a range from −1 to +1. For example, the amplitude limit gradation change amount Xlm is +1, and the flat width is 7 pixels from the change of the gradation value. When the flat width data predicted value dst = 7 is input, the calculated slope divk is 1/7. When the amplitude limit gradation change amount Xlm is −1, the slope divk = −1 / 7. When the flat width data predicted value dst = 0, the slope divk = Xlm. Therefore, the slope divk is obtained as a value in the range from −1 to +1.

  The switching means 42 includes a gradation change position signal Pt from the gradation change position detection means 13 in the gradation change detection means 10, an inclination divk calculated by the inclination calculation means 41, and one pixel from the inclination delay means 43. The delayed delay slope data value pKsl is input. The switching means 42 switches the slope divk calculated by the slope calculation means 41 and the delay slope data value pKsl from the slope delay means 43 in accordance with the gradation change position signal Pt, thereby changing the slope of the horizontal gradation value. The detected inclination data value Ksl is output.

  That is, the switching means 42 selects the inclination divk calculated by the inclination calculation means 41 at the pixel position (Pt = 1) where the gradation value changes based on the gradation change position signal Pt, and sets it as the inclination data value Ksl. On the other hand, in the gradation flat section (Pt = 0) in which the gradation value does not change, the switching means 42 changes the delay slope data value pKsl (that is, the gradation value before the current pixel position) from the slope delay means 43. Corresponding to the slope divk at the selected pixel) and select the slope data value Ksl. The inclination data value Ksl is output to the correction bit generation means 50 as an inclination detection result in the inclination detection means 40 and is also sent to the inclination delay means 43, delayed by one pixel, and switched as a delay inclination data value pKsl. Returned to

  The slope delay means 43 delays the slope data value Ksl from the switching means 42 by one pixel and outputs a delayed slope data value pKsl. Since the slope delay means 43 delays the output from the switching means 42, the slope slope data value pKsl is outputted as it is, and the slope data value Ksl of the immediately preceding pixel is output as it is, and the slope divk calculated for each pixel position where the gradation value changes. The value is held until the pixel position where the gradation value changes next.

  Therefore, the gradient of the gradation value calculated by the inclination calculation means 41 is obtained as the inclination data value Ksl for each pixel position (Pt = 1) where the gradation value changes by the switching means 42 and the inclination delay means 43, In the tone flat section, the value of the pixel whose gradation value has changed before that is held and output.

FIGS. 9A and 9B are diagrams for explaining the inclination data value Ksl indicating the inclination of the gradation value obtained by the inclination detecting means 40. FIG. 9A shows the amplitude limit gradation change amount Xlm. When the gradation value of the gradation increases at +1, FIG. 5B shows the case where the gradation value decreases when the amplitude limit gradation change amount Xlm is −1. 9A and 9B, the horizontal axis indicates the pixel position in the horizontal direction, and the vertical axis indicates the gradation value La (x) of the input image signal Da at each pixel position. FIG. 9 (a) and (b), the the flat width data prediction value dst and amplitude limit gradation variation Xlm the gradation value is obtained at the pixel position x ₀ which varies, FIG. 9 (a) and as the slope as shown by a broken line which is inclined (b), the inclination data value Ksl the pixel position x ₀ after the gradation value indicated by the gradation change position signal Pt = 1 is changed is obtained.

  As described above, the inclination detecting means 40 outputs the inclination of the gradation value at the pixel position where the gradation value indicated by the gradation change position signal Pt = 1 changes as the inclination data value Ksl. The value of the pixel whose gradation value has changed before that is held. Since the amplitude limit gradation change amount Xlm is limited within the range from −1 to +1, the detected slope data value Ksl is a value within the range from −1 to +1.

<< 1-2-6 >> Correction bit generation means
Next, the correction bit generation means 50 will be described in detail. The correction bit generation means 50 includes the inclination data value Ksl from the inclination detection means 40, the initialization signal Sif from the timing signal generation means 100, and the gradation from the gradation change position detection means 13 of the gradation change detection means 10. The change position signal Pt, the amplitude limit gradation change amount Xlm from the change amount restriction means 12 of the gradation change detection means 10, and the correction limit coefficient rc from the correction limit coefficient setting means 30 are input. The correction bit generation means 50 obtains the gradation change amount dK for each adjacent pixel of the correction value (correction bit data) to be added to the gradation value of the input pixel signal Da from the inclination data value Ksl, and uses the initialization signal Sif to determine the horizontal level. Initialization is performed for each direction scanning period (value is set to “0”), and the correction value aCd is calculated from the gradation change amount dK, the amplitude limit gradation change amount Xlm, and the correction limit coefficient rc in accordance with the gradation change position signal Pt. Then, correction bit data Cd based on the correction value aCd is generated and output to the pixel value calculation means 62. Here, the gradation change amount dK obtained from the inclination data value Ksl is a value including a decimal part with respect to the gradation value La (x) (see FIG. 2A) of the input image signal Da. The correction bit data Cd generated by the correction bit generation means 50 is obtained as a bit string including an additional bit E having a value including the decimal part of the gradation value of the input image signal Da and a sign bit of the value to be added.

  FIG. 10 is a block diagram schematically showing an example of the configuration of the correction bit generation means 50. The correction bit generation unit 50 includes, for example, a calculation unit 51, a subtraction unit 52, a switching unit 53, a correction value delay unit 54, and a bit string conversion unit 55. The correction bit generation means 50 obtains a correction value (gradation value) to be added to the input pixel signal Da, and outputs a bit string indicating the gradation value as correction bit data Cd.

  In FIG. 10, the amplitude limiting gradation change amount Xlm from the gradation change amount limiting unit 12 and the correction limit coefficient rc from the correction limit coefficient setting unit 30 are input to the calculation unit 51. The computing means 51 calculates a correction value mCd from the amplitude limit gradation change amount Xlm and the correction limit coefficient rc. Of the correction value mCd obtained by the calculation means 51, the correction value mCd at the pixel position where the gradation value changes (the gradation change amount is not 0, Pt = 1 pixel) is used by the switching means 53 described later. The correction limit coefficient rc set by the correction limit coefficient setting means 30 in FIG. 5 is a multiplication value for the gradation correction value and is set within a range from 0 to 1. Therefore, the correction value mCd is the amplitude limit gradation. The change amount Xlm is multiplied by the correction limiting coefficient rc, and the result is calculated as a multiplication result (rc) × (Xlm).

  The amplitude limit gradation change amount Xlm is limited within a range from −1 to +1 corresponding to the value of one gradation of the input image signal Da, and the correction limit coefficient rc is the magnitude of the gradation change amount dfx. Therefore, the correction value mCd based on the multiplication result (rc) × (Xlm) is a pixel having a large gradation change amount dfx and an edge of the image in the vicinity (correction limiting coefficient). In the case of rc = 0), the correction value mCd = 0, and in other pixels, the absolute value in the range from −1 to +1 is expressed as a decimal that is 1 or less.

  The correction limit coefficient rc from the correction limit coefficient setting unit 30 is set as a multiplication value for the correction value, and the calculation unit 51 exemplifies a case where the amplitude limit gradation change amount Xlm is multiplied by the correction limit coefficient rc. By using a ROM or the like holding a data conversion table, the correction value mCd may be obtained from the amplitude limit gradation change amount Xlm in accordance with the value of the correction limit coefficient rc, and depending on the value of the correction limit coefficient rc. Thus, the correction value mCd may be converted into a fixed value, and any means that can limit the value of the correction value according to the correction limiting coefficient rc may be used.

  The subtraction means 52 receives the inclination data value Ksl from the inclination detection means 40 and the delay correction value pCd delayed by one pixel from the correction value delay means 54. The subtracting means 52 obtains the gradation change amount dK for each adjacent pixel of the correction value from the inclination data value Ksl, and subtracts the gradation change amount dK from the correction value in the immediately preceding pixel that is the delay correction value pCd. The correction value sCd in the gradation flat section after the pixel position (Pt = 1) where the gradation value changes is obtained, and the obtained correction value sCd is output to the switching means 53.

  That is, the subtraction means 52 first obtains the value of the slope data value Ksl as the gradation change amount dK for each adjacent pixel of the correction value (dK = Ksl), and then the correction value (delay correction value) for the immediately preceding pixel. The gradation change amount dK is subtracted from pCd) (pCd−dK). The subtraction of the subtracting means 52 is performed by subtraction or addition processing according to the sign of the gradation change amount dK (that is, the sign of the slope data value Ksl) (when dK> 0, the absolute value | dK | is subtracted). When dK <0, the absolute value | dK | is added.) When the sign of the value after subtraction is inverted (+ changes to − or − changes to +), the delay correction value pCd is In the case of subtraction processing with “0”, the correction value sCd is output as “0” (sCd = 0). Accordingly, the correction value sCd in the gradation flat section after the pixel position (Pt = 1) where the gradation value changes is the magnitude of the absolute value of the gradation change amount dK in order from the change position (that is, the slope data value Ksl). The absolute value of | Ksl |) is changed. Here, since the slope data value Ksl is a value in the range from −1 to +1, the correction value sCd is expressed as a decimal number whose absolute value in the range from −1 to +1 is 1 or less.

  The switching means 53 receives the initialization signal Sif, the gradation change position signal Pt, the correction value mCd from the calculation means 51, and the correction value sCd from the subtraction means 52. Based on the initialization signal Sif and the gradation change position signal Pt, the switching unit 53 selects one of the correction value mCd from the calculation unit 51, the correction value sCd from the subtraction unit 52, and the initialization value “0”. The selected value is output as a correction value aCd which is a gradation value to be added to the input image signal Da.

  Specifically, the switching means 53 selects the initialization value “0” and outputs it as the correction value aCd = 0 when the input initialization signal Sif indicates initialization at the interval of the horizontal scanning period. To do. Further, when the gradation change position signal Pt is a value indicating the pixel position where the gradation value changes (Pt = 1), the switching means 53 is obtained from the amplitude restriction gradation change amount Xlm and the correction restriction coefficient rc. The correction value mCd from the calculating means 51 is selected and output as the correction value aCd. On the other hand, when the gradation change position signal Pt is a value (Pt = 0) indicating the gradation flat section position where the gradation value does not change, the switching means 53 determines the correction value sCd (that is, the immediately preceding pixel) by the subtraction means 52. (A value obtained by subtracting the gradation change amount dK = Ksl) from the correction value pCd, and outputs the correction value aCd. Then, the correction value aCd output from the switching unit 53 is sent to the bit string conversion unit 55 and the correction value delay unit 54. The correction value delay means 54 delays the input correction value aCd by one pixel and returns it to the subtraction means 52 as a delay correction value pCd.

  Since the correction value delay means 54 delays the correction value aCd from the switching means 53 by one pixel to obtain the delay correction value pCd, the correction value for the immediately preceding pixel is output as the delay correction value pCd.

The correction value aCd added to the input image signal Da at the pixel position (Pt = 1) where the gradation value changes by the calculation means 51, subtraction means 52, correction value delay means 54, and switching means 53 described above. Is a correction value mCd obtained from the amplitude limit gradation change amount Xlm and the correction limit coefficient rc. At this time,
mCd = (rc) × (Xlm)
It is.

  Further, in the gray level flat section (Pt = 0) where the gray level value does not change, the correction value aCd added to the input image signal Da becomes the correction value sCd output from the subtracting means 52. At this time, the correction value sCd is a value obtained by subtracting the gradation change amount dK = Ksl from the value in the previous pixel in order from the pixel position (Pt = 1) where the gradation value changes, and the level of the gradation change amount dK. It is obtained as a value that sequentially changes to 0 due to the difference (see FIGS. 2C and 3C). The correction value based on the multiplication result (rc) × (Xlm) and the gradation change amount dK based on the inclination data value Ksl are both expressed as decimal numbers whose absolute value in the range from −1 to +1 is 1 or less. The correction value aCd obtained from the switching means 53 is also a gradation value having an accuracy that is a decimal number of 1 or less.

For example, assuming that the pixel position where the gradation value changes (pixel position of Pt = 1) as the starting point and the value obtained by sequentially counting the subsequent gradation flat sections is the count value N, the gradation change position signal Pt = 1. The gradation change amount of the correction value aCd at each pixel position from the count value N = 0 (correction value mCd) at N × Ksl is determined by the count value N and the gradient data value Ksl (gradation change amount dK = Ksl). The correction value aCd is expressed by the following equation: aCd = mCd−N × Ksl
Can be obtained. That is, in order from the position of the correction value mCd, a value having a change in level difference of the gradation change amount dK due to the inclination data value Ksl becomes the correction value aCd.

The correction value mCd at the pixel position where the gradation value changes is expressed by the following equation: mCd = (rc) × (Xlm)
Therefore, in the pixel area where the gradation value changes continuously and gradually in the horizontal direction, which is the difference between +1 and −1, the gradation change amount dK is changed in order from the pixel position where the gradation value changes. The correction value aCd has a change in level difference. On the other hand, if it is determined that the change in the gradation value is caused by the edge of the image, the correction limit coefficient rc = 0 and the correction value mCd = 0. Since the correction value is 0 even in the pixel, the gradation value is not added. Therefore, according to Embodiment 1, it is possible to obtain a correction value that maintains the sharpness (contour information) of an image.

  The bit string conversion means 55 receives the correction value aCd from the switching means 53. The bit string conversion means 55 converts the correction value aCd into a bit string value having a predetermined number of bits, obtains an addition bit E indicating the value to be added and a sign bit of the value as correction bit data Cd, and a pixel value calculation means To 62. Since the absolute value excluding the sign of the correction value aCd is obtained as a value including a decimal number of 1 or less, the correction value (additional bit E) in the correction bit data Cd is obtained with respect to the bit string of the gradation of the input image signal Da. The decimal part will be shown.

  Here, when the additional bit E in the correction bit data Cd is generated with 4 bits and added to the lowest order side of the input image signal Da, for example, the absolute value of the correction value aCd excluding the sign is the value of a 4-bit bit string. Convert to However, at this time, the value that becomes the integer part 1 of −1 and +1 is 16 in the bit string. Therefore, this value is limited to 4 bits, and the value in the bit string is obtained as 15. In this way, the bit string conversion means 55 converts the correction value aCd into a bit string value having a predetermined number of bits and also performs a value limiting process. Then, the bit string converting means 55 generates and outputs the converted 4-bit additional bit E as corrected bit data Cd together with a sign bit (having a bit number of 1 bit or more) indicating the sign of the correction value aCd.

  The correction bit generation means 50 of FIG. 10 is provided with the bit string conversion means 55 so that the correction value aCd is obtained as correction bit data Cd based on the bit string of the sign bit and the additional bit E of 4 bits. Since the value aCd or the like is usually obtained as a value of a predetermined number of bits, it can be used as the correction bit data Cd as it is. In some cases, the correction value does not need to be handled as a bit string as in the case of software. Therefore, the bit string conversion means 55 can be omitted.

<< 1-2-7 >> Delay compensation means 61.
When the input image signal Da is input to the delay compensation unit 61, the delay compensation unit 61 matches the delay until the correction bit data Cd output from the correction bit generation unit 50 is obtained with the pixel position of the input image signal Da. Thus, the delay compensation of the input image signal Da is performed, and the image signal Dd subjected to delay compensation is output.

<< 1-2-8 >> Pixel value calculation means 62.
The pixel value calculation unit 62 receives the delay compensated image signal Dd from the delay compensation unit 61 and the correction bit data Cd from the correction bit generation unit 50. The pixel value calculation unit 62 calculates a new output image signal Db by subtracting the correction bit data Cd from the correction bit generation unit 50 by matching the position of the integer part with respect to the delay-compensated image signal Dd. ,Output. Since correction bit data Cd including a decimal part is added to the gradation value of the output image signal Db by calculation, the bit number of the output image signal Db is larger than the bit number of the image signal Dd, that is, expanded. The output image signal Db in which the number of bits is extended becomes the output of the gradation converting means 1.

  The pixel value calculation means 62 performs subtraction or addition processing according to the sign of the correction bit data Cd in the calculation processing for subtracting the correction bit data Cd from the image signal Dd (that is, when Cd> 0, The absolute value | Cd | is subtracted, and if Cd <0, | Cd | is added). Further, when the calculated value becomes a negative value, the pixel value calculation means 62 sets the output image signal Db to “0” (Db = 0) and sets the number of bits (maximum value) set in the output image signal Db. If the value exceeds the value, the value is set to the maximum value, and the value of the output image signal Db is limited.

  As described above, the additional bit E indicating the value to be added in the correction bit data Cd includes a decimal part with respect to the gradation value of the delay-compensated image signal Dd (or input image signal Da). The output image signal Db after the calculation processing by addition or subtraction in the pixel value calculation means 62 is an image signal with a precision having a decimal part with respect to the image signal Dd. That is, since the number of bits of the output image signal Db is larger than that of the image signal Dd, not only the number of gradations that can be expressed is increased, but also the number of bits in the decimal part by the correction bit Cd including the decimal part is included. The resolution of the tone value is increased, and a smoother change in the gradation value can be expressed. When the change in the gradation value is caused by the edge of the image, the correction bit data Cd is obtained as 0. As a result, no gradation is added to the pixel adjacent to the edge portion of the image. While maintaining the sharpness (contour information) of Db, it is possible to increase the smoothness of the image in the pixel region where the gradation value gradually changes other than the edge of the image.

  FIG. 11 shows the input image signal Da (or the delay compensated image signal Dd from the delay compensation means 61), the correction bit data Cd from the correction bit generation means 50, and the output image output from the pixel value calculation means 62. It is a figure which shows the relationship of the signal Db. Here, a case will be described where the input image signal Da (or image signal Dd) is m = 8 bits, the correction bit data Cd is a sign bit and an additional bit E4 bits, and the output image signal Db is n = 12 bits.

  In FIG. 11, since the correction bit data Cd is obtained as an additional bit E indicating a decimal part with respect to the input image signal Da, the pixel value calculation means 62 aligns the position of the integer part and the least significant part of the image signal Dd. The output image signal Db is calculated by subtracting or adding a value obtained by adding the additional bit E (4 bits) of the correction bit data Cd to a position lower than the bit according to the sign. That is, the pixel value calculation means 62 performs a process corresponding to adding the value of the additional bit E to the least significant side of the image signal Dd, and generates a 12-bit output image signal Db. In the output image signal Db, the bit string is expanded to the lower bit side with respect to the image signal Dd, that is, the decimal part is added to the gradation value of the original input image signal Da. The resolution of one gradation of Db is higher than that of the image signal Dd (16 times in FIG. 11), quantization noise or pseudo contour is further reduced, and an accurate gradation can be expressed.

<< 1-3 >> Operation.
In the gradation conversion means 1, using the gradation change information based on the gradation change amount dfx, cyclic filter processing is performed on the flat width of the gradation flat section up to the pixel immediately before the pixel at the gradation change position. The flat width data predicted value dst obtained by predicting the flat width of the gray level flat section after the pixel immediately after the pixel at the gray level change position is obtained, and the gray level is calculated from the amplitude limit gray level change amount Xlm and the flat width data predicted value dst. An inclination data value Ksl indicating the inclination of the value is obtained. Then, the gradation converting means 1 generates correction bit data Cd from the amplitude limit gradation change amount Xlm, the gradient data value Ksl, and the correction limit coefficient rc, and adds the correction bit data Cd to the input image signal Da. Since the number of bits of the image signal is expanded and the gradation value is corrected, when the gradation value changes, it is necessary to hold the image signal for the flat width of the gradation flat section in a memory or the like. Absent. For this reason, according to the first embodiment, the pixel area in which the gradation value gradually changes without significantly increasing the circuit scale, or the case where it is determined that the change in the gradation value is caused by the edge of the image. 12-bit output image signal Db in which the gradation value change is more smoothly converted is obtained.

  Next, the operation of the image processing apparatus according to the first embodiment will be described more specifically.

  FIG. 12 shows the image processing apparatus according to the first embodiment, which performs gradation conversion by adding the correction bit data Cd to the input image signal Da to expand the number of bits, thereby converting the level of the original input image signal Da. It is a flowchart explaining operation | movement of the gradation conversion means 1 output as the output image signal Db containing a decimal part with respect to a tone value. In the processing in the gradation converting unit 1, initialization is performed for each horizontal synchronization signal by the initialization signal Sif from the timing signal generating unit 100. However, in FIG. This is shown as processing for each pixel in each scanning line (line).

  FIGS. 13A to 13K are diagrams showing a part of signals when the gradation values of the input image signal Da shown in FIGS. 2A to 2C are gradually increasing one gradation at a time. FIGS. 13A and 13B are diagrams for explaining the operation of the tone conversion unit 1; FIG. 13A shows the horizontal pixel position x of the input image signal Da, FIG. 13B shows the input image signal Da, and FIGS. (E) is a gradation change amount dfx based on a difference in gradation values between adjacent pixels obtained by the gradation change detection means 10, an amplitude-limited gradation change amount Xlm of the gradation change amount dfx, and a gradation change position signal. Pt, FIG. 13 (f) is a flat width count value Cnt output from the flat width count means 21 in the flat width prediction means 20, and FIG. 13 (g) is a cyclic filter processing means 22 in the flat width prediction means 20. Predicted flat width data dst predicted flat width output from FIG. 3 (h) is an inclination data value Ksl output from the inclination detecting means 40, FIG. 13 (i) is a correction value aCd obtained by the correction bit generating means 50, and FIG. 13 (j) is a correction bit in the pixel value calculating means 62. A value obtained by adding the data Cd to the image signal Dd (that is, the input image signal Da) is a gradation value when the minimum gradation value of the image signal Dd is represented as 1. FIG. The output image signal Db that is the output of the correction bit data Cd is shown, and the additional bit E in the correction bit data Cd is 4 bits. In FIGS. 13A to 13K, pixel data is input in order from the left, and the horizontal axis indicates the pixel position in the horizontal scanning direction. In FIGS. 13A to 13K, in order from the pixel position x = 8, 8 pixels with gradation value La (x) = 2, 8 pixels with gradation value La (x) = 3, When the pixels with the gradation value La (x) = 4 are aligned with 8 pixels,... And the input image signal Da is m = 8 bits, the left pixel position x = 8 with respect to this 8-bit image signal. The image becomes brighter continuously by one gradation from right to left.

  FIGS. 14A to 14K show a part of the signal of the portion where the gradation value of the input image signal Da shown in FIGS. 3A to 3C is gradually decreased by one gradation. FIGS. 14A and 14B are diagrams for explaining the operation in the gradation converting means 1, and the signals in FIGS. 14A to 14K are the same signals as those in FIGS. 13A to 13K. 14A to 14K, the gradation value La (x) = 1 changes from the gradation value La (x) = 1 to the gradation value La (x) = 8 at the pixel position x = 8, and the subsequent pixel position x Then, in order, there are 8 pixels with gradation value La (x) = 8, 8 pixels with gradation value La (x) = 7, 8 pixels with gradation value La (x) = 6, and so on. The change of the gradation value difference 7 at the pixel position x = 8 with respect to the 8-bit input image signal Da is an image that becomes darker continuously by one gradation after that due to the contour (edge) of the image. Become.

Hereinafter, the operation of the gradation converting means 1 will be described with reference to FIGS. 12, 13A to 13K, and 14A to 14K. When an m-bit input image signal Da (gradation value La (x)) as shown in FIGS. 13B and 14B is input to the gradation converting means 1 (step S101 in FIG. 12), The input image signal Da is input to the gradation change detection means 10, and the gradation change amount calculation means 11 in the gradation change detection means 10 determines the difference in gradation values between pixels adjacent in the horizontal direction (that is, immediately before (Difference from pixel x−1) is calculated, and the gradation change amount dfx is expressed by the following equation: dfx = La (x) −La (x−1)
(Step S102). For example, in FIG. 13C, dfx = La (8) −La (7) is calculated at the pixel position x = 8, and dfx = + 1. Similarly, dfx = + 1 at pixel positions x = 16, 24, and 32. Further, in FIG. 14C, dfx = La (8) −La (7) is calculated at the pixel position x = 8 and dfx = + 7, and at the pixel positions x = 16, 24, and 32, dfx = −1. It becomes.

  In FIG. 12, the gradation change amount dfx obtained by the gradation change amount calculating means 11 is output to the correction limit coefficient setting means 30 (step S104), and the gradation change amount in the gradation change detecting means 10 is displayed. It is output to the limiting means 12 and the gradation change position detecting means 13. The gradation change amount limiting means 12 and the gradation change position detecting means 13 are based on the amplitude limit gradation change amount Xlm in which the value of the gradation change amount dfx is limited within a predetermined range and the value of the gradation change amount dfx. A gradation change position signal Pt, which is a result of detecting whether the tone value has changed, is obtained (step S103).

  The amplitude limit gradation change amount Xlm has a value such that the gradation change amount dfx is within a predetermined gradation value range, that is, a range from −1 to +1 (indicated by TH = 1 in FIG. 12). In order to detect a change in one gradation of the input image signal Da, the range of restriction is set to −1 to +1. That is, the value of the amplitude limit gradation change amount Xlm is represented by three values of −1, 0, and +1. FIGS. 13D and 14D show the amplitude limit gradation change amount Xlm, and the amplitude limit gradation change amount Xlm is limited to +1 or −1 at the position where the gradation value changes. In the gradation flat section where the tone value does not change, the amplitude limited gradation change amount Xlm = 0.

  The gradation change position signal Pt is obtained as a result of detecting the position of a pixel whose gradation value changes from the value of the gradation change amount dfx. When the absolute value of the gradation change amount dfx is larger than 0 and there is a difference of one gradation or more, if it is determined that there is a change in the gradation value, the gradation change position signal Pt = 1 is set and the gradation change amount dfx is set. If it is determined that the gradation value is flat without changing the gradation value, the gradation change position signal Pt = 0. 13E, the pixel position x = 8, 16, 24, 32. In FIG. 14E, the gradation change position signal Pt = 1 at the pixel position x = 8, 16, 24, 32. . Note that the gradation change position signal Pt has a predetermined gradation value difference, and it is only necessary to indicate the position of the pixel where the gradation value changes. It is also possible to set the value of the limited gradation change amount Xlm. As described above, the gradation change detecting means 10 detects the gradation change amount in the horizontal direction and the pixel position where the gradation value changes in the input image signal Da, and determines the gradation change amount dfx and the gradation change amount. An amplitude-limited gradation change amount Xlm by dfx and a gradation change position signal Pt are obtained.

  Next, in the flat width counting means 21 in the flat width predicting means 20, the count value is initialized for each horizontal scanning period by the initialization signal Sif (the count value is set to 0) and is indicated by the gradation change position signal Pt. Using the pixel position as a reference, the number of pixels in a flat period with no change in gradation value in the horizontal direction up to the immediately preceding pixel is obtained, and set as a flat width count value Cnt (steps S105 and S106). Specifically, first, initialization is performed for each horizontal scanning period by the initialization signal Sif, and the number of pixels in the horizontal direction is counted on the basis of the gradation change position signal Pt. The flat width of the flat section and the pixel count value Cnt0 are obtained (step S105). Then, the pixel count value Cnt0 is delayed by one pixel to obtain a flat width count value Cnt that is a flat width up to the pixel immediately before the target pixel position (step S106).

  In FIG. 13F, the pixel count value Cnt0 is reset to “0” at the pixel positions x = 8, 16, 24, and 32 where the gradation change position signal Pt = 1, so that the next pixel position At (x + 1), the flat width count value Cnt becomes “0”. At the pixel position x where the gradation change position signal Pt = 1, the flat width which is the number of pixels counted up to the previous pixel x−1, that is, the flat number indicating the continuous number of pixels where the gradation change amount dfx = 0. A width count value Cnt is obtained. The same applies to FIG.

  Next, in FIG. 12, a flat width data predicted value dst, which is a value obtained by predicting the flat width by the cyclic filter processing means 22 in the flat width predicting means 20, is obtained, and the inclination detecting means 40 determines the horizontal gradation value. The operation of obtaining the inclination data value Ksl from which the inclination has been detected is performed at the pixel position where the gradation value indicated by the gradation change position signal Pt = 1 changes.

The recursive filter processing means 22 initializes the output result for each horizontal scanning period by the initialization signal Sif, and the gradation value indicated by the gradation change position signal Pt = 1 with respect to the flat width count value Cnt. A cyclic filter process is performed for each pixel position where the change in the pixel value, and the result of this filter process is set as a flat width data predicted value dst that is a predicted flat width after the pixel position where the gradation value changes (step S107). , S110). The calculation of the recursive filter processing constitutes a low-pass filter, and in FIG. 12, for example, (pdst + Cnt) / 2 (the above equation (1)) with respect to the delayed flat width data predicted value pdst and the flat width count value Cnt. The cyclic filter processing is performed using the coefficients k ₁ = 1/2 and k ₂ = 1/2). On the other hand, in the gradation flat section (Pt = 0) other than the gradation change position signal Pt = 1, the value of the pixel whose gradation value has changed before that is held and output (step S120).

  The flat width data predicted value dst is a low-frequency component of the flat width when the gradation value changes in the horizontal direction. Therefore, in the pixel region where the gradation value changes continuously in the horizontal direction, A flat width value detected when the gradation value changes can be obtained without abrupt change. Thus, the flat width data predicted value dst can be used as a value predicting the flat width of the change in the gradation value after the pixel position where the gradation value indicated by the gradation change position signal Pt = 1 changes. . Further, since the flat width data predicted value dst, which is a value obtained by predicting the flat width by the cyclic filter processing, is obtained, the memory to be used is not related to the pixel range corresponding to the detected flat width and should be constant. Even in a section where the gradation value changes very slowly, the flat width data predicted value dst, which is a predicted flat width, can be obtained, and the gradation value can be changed without significantly increasing the circuit scale. The width of the gradation flat section can be obtained.

  In FIG. 13 (g) and FIG. 14 (g), the flat width data predicted value pdst at x−1 one pixel before at the pixel position x = 8, 16, 24, 32 where the gradation change position signal Pt = 1 is obtained. Then, the cyclic filter processing by (pdst + Cnt) / 2 is performed on the flat width count value Cnt (FIG. 13 (f) and FIG. 14 (f)). In the gradation flat section (Pt = 0), values at pixel positions x = 8, 16, 24, and 32 are held.

  The inclination detection means 40 detects the horizontal direction of the input image signal Da from the amplitude limit gradation change amount Xlm and the flat width data predicted value dst at the pixel position where the gradation value indicated by the gradation change position signal Pt = 1 changes. The gradient data value Ksl is obtained (steps S107 and S111 in FIG. 12). That is, the inclination data value Ksl is calculated as the inclination data value Ksl = Xlm / dst from the amplitude limit gradation change amount Xlm and the flat width data predicted value dst for each gradation change position signal Pt = 1 (Step 1). S111). In the gradation flat section (Pt = 0) other than the gradation change position signal Pt = 1, the value of the pixel whose gradation value has changed before that is held (step S120).

  Since the amplitude limit gradation change amount Xlm is input as a value in which the gradation change amount dfx is limited within a range from −1 to +1 (in step S103), the gradient data value Ksl of the detected gradation value is set. Is also in the range from -1 to +1.

  According to FIG. 13H, at the pixel position x = 8 at which the gradation change position signal Pt = 1, the inclination data value Ksl = + 1/4, and similarly, the inclination at the pixel position x = 16, 24, 32. A data value Ksl is determined. Further, according to FIG. 14H, the inclination data value Ksl = + 1/4 at the pixel position x = 8 at which the gradation change position signal Pt = 1, and the inclination data value Ksl = at the pixel position x = 16. Similarly, the inclination data value Ksl is obtained at the pixel position x = 16, 24, 32. In both FIG. 13 (h) and FIG. 14 (h), values at pixel positions x = 8, 16, 24, and 32 are held in the gradation flat section (Pt = 0).

  The correction limit coefficient setting unit 30 sets the correction limit coefficient rc from the magnitude of the absolute value of the gradation change amount dfx (step S104 in FIG. 12). The correction limiting coefficient rc is obtained as a value that can limit the correction value so that the gradation value is not added to the image signal at the edge of the image. For example, the correction restriction coefficient rc is a multiplication value for the gradation correction value. To a value in the range from 1 to 1.

  Here, since the gradation change amount dfx is obtained from the difference in gradation value between adjacent pixels, the gradation difference due to the edge component of the image is also included in the pixels near the edge of the image. The pixel area where the number of gradations is expanded is an area in which the gradation value changes smoothly and changes by a difference of one gradation, so it is necessary to prevent the correction value from being added at the edge of the image. Therefore, it is determined from the magnitude of the gradation change amount dfx whether or not the difference in gradation value in the pixel adjacent to the edge of the image is due to the edge of the image, and the correction limiting coefficient rc is set based on the result. To do.

  As an example, the maximum difference absolute value dfm is obtained from the absolute value of the gradation change amount dfx when the gradation value changes and the magnitude of the low frequency component of the gradation change amount dfx, and the characteristics as shown in FIG. If the correction limit coefficient rc is determined as rc = 0 to 1 by converting in the above, the correction limit coefficient rc has a value of rc = 0 for pixels determined to have an image edge in the vicinity of the pixel whose gradation value changes. Therefore, the correction value is limited by the value. By using the low-frequency component of the gradation change amount dfx, not only the gradation change amount dfx, also consider the change in the gradation value due to the edge of the image in the pixel near the pixel position where the gradation value changes. It is possible to determine whether or not the pixel has an image edge with higher accuracy.

  13A to 13K, the gradation change amount dfx (FIG. 13A) is obtained at any of the pixel positions x = 8, 16, 24, and 32 where the gradation change position signal Pt = 1. Since dfx = + 1, the correction limiting coefficient rc is always the correction limiting coefficient rc = 1 (not shown). In the case of FIGS. 14A to 14K, the gradation change amount dfx (FIG. 14A) at the pixel position x = 8 is dfx = + 7, and therefore the correction limiting coefficient rc at this position is rc = 0. However, at other pixel positions x = 16, 24, and 32, the gradation change amount dfx = + 1, so that the correction limiting coefficient rc is rc = 1.

  Next, the correction bit generation means 50 is initialized for each horizontal scanning period by the initialization signal Sif, and the gradation change amount dK and the amplitude-limited gradation change by the inclination data value Ksl according to the gradation change position signal Pt. Correction bit data Cd is generated from the amount Xlm and the correction limiting coefficient rc (steps S112 to S114, S121 to S122, and S130 and S131 in FIG. 12).

  More specifically, the correction bit generation means 50 initializes a correction value aCd, which is a gradation value to be added to the input image signal Da, at the boundary of the horizontal scanning period indicated by the initialization signal Sif. The process of generating the correction value aCd is switched according to the gradation change position signal Pt obtained from the change amount dfx (step S112).

  When the gradation change position signal Pt = 1 at which the gradation value changes (step S112), the amplitude limit gradation change amount Xlm is multiplied by the correction restriction coefficient rc, and the correction value mCd = (rc) × (Xlm) is calculated (step S113). Then, the obtained correction value mCd is determined as the correction value aCd (step S114). The amplitude limit gradation change amount Xlm is limited within a range from −1 to +1 corresponding to the value of one gradation of the input image signal Da, and the correction limit coefficient rc is the magnitude of the gradation change amount dfx. Therefore, the correction value mCd is a correction value mCd = 0 at a pixel (correction limiting coefficient rc = 0) in which the gradation change amount dfx is large and the edge of the image exists in the vicinity. In other pixels, the absolute value in the range from −1 to +1 is expressed as a decimal number that is 1 or less.

  On the other hand, in the gradation flat section where the gradation change position signal Pt = 0 (step S112), the gradient data value Ksl is set as the gradation change amount dK for each adjacent pixel of the correction value (dK = Ksl), and immediately before. The gradation change amount dK is subtracted (pCd−dK) from the correction value (delay correction value pCd) in the pixel to obtain the correction value sCd in the gradation flat section (step S121). In addition, after the subtraction, when the sign of the correction value sCd is inverted from the delay correction value pCd (+ changes to − or − changes to +), and when the delay correction value pCd is “0”, The correction value sCd is output as “0” (sCd = 0). Then, the correction value sCd is determined as the correction value aCd (step S122). As a result, the correction value sCd in the gradation flat section becomes a value that changes in order of the absolute value of the gradation change amount dK from the change position (that is, the absolute value | Ksl | of the gradient data value Ksl). Here, since the slope data value Ksl is a value in the range from −1 to +1, the correction value sCd is also expressed as a decimal number whose absolute value in the range from −1 to +1 is 1 or less.

  The correction value aCd obtained as described above is converted into a bit string value having a predetermined number of bits, and is obtained as correction bit data Cd including an additional bit E indicating a value to be added and a sign bit of the value (step S130). ). The correction value aCd is delayed by one pixel and sent to the next pixel process as the correction value pCd for the immediately preceding pixel (step S131).

  From the above operation, the correction value aCd (that is, the correction bit data Cd) to be added to the input image signal Da is corrected to the amplitude limit gradation change amount Xlm at the pixel position (Pt = 1) where the gradation value changes. In a gradation flat section (Pt = 0) obtained as a correction value aCd = (rc) × (Xlm) by the limiting coefficient rc, the gradient is sequentially increased from the value at the pixel position where the gradation value changes. It is obtained as a value that sequentially changes to 0 due to the difference in gradation value by the data value Ksl. Both the correction value based on the multiplication result (rc) × (Xlm) and the slope data value Ksl are expressed as decimal numbers whose absolute value in the range from −1 to +1 is 1 or less, and therefore the correction value aCd is also expressed. 1 is a gradation value having an accuracy of a decimal number of 1 or less.

  In addition, since the correction value mCd = (rc) × (Xlm) is obtained using the correction limiting coefficient rc, in the pixel region where the gradation value changes gradually, the pixel position where the gradation value changes sequentially. The correction value aCd has a change in the gradation value difference of the gradation change amount dK. On the other hand, if it is determined that the change in the gradation value is caused by the edge of the image, the correction value mCd = 0. The correction value is 0 even in the subsequent pixels, and can be obtained as a correction value that preserves the contour information of the image.

  According to FIG. 13I, the correction value aCd = + 1 at the pixel position x = 8 where the gradation change position signal Pt = 1, and the correction at the pixel position x = 8 in the subsequent gradation flat section. The correction value aCd having a change of the gradation value difference −1/4 due to the inclination data value Ksl (ie, 3/4, 2/4, 1/4, 0 in order of the pixel from the value aCd = + 1) , Corrected bit data Cd). Similarly, at the pixel position x = 24, the correction value aCd = + 1, and in the subsequent pixels with the gradation change position signal Pt = 0, the correction value aCd = + 1 at the pixel position x = 24 is sequentially 6/7. , 5/7, 4/7,..., 5/7,..., 5/7,...

  Further, according to FIG. 14 (i), the correction value aCd = −1 at the pixel position x = 16 at which the gradation change position signal Pt = 1, and in the subsequent gradation flat section, the pixel position x = 16, correction values aCd = −1, in order from −5/6, −4/6, −3/6,... It is obtained as a value aCd (that is, correction bit data Cd). Similarly, the correction value aCd = −1 at the pixel position x = 24, and in the subsequent pixels with the gradation change position signal Pt = 0, the correction value aCd = −1 at the pixel position x = 24 in order, − 6/7, -5/7, -4/7, and so on, are obtained as correction values aCd having a change of the gradation value difference +1/7 by the inclination data value Ksl. At the pixel position x = 8, the gradation change amount dfx = + 7 and the correction limiting coefficient rc = 0, so that the correction value aCd = 0. Therefore, the correction value aCd (that is, the correction bit data Cd) is 0 even in the subsequent gray level flat section.

  The pixel value calculation unit 62 applies correction bit data Cd to the correction bit data Cd from the correction bit generation unit 50 and the image signal Dd (or input image signal Da) that has been delay compensated so as to match the pixel position of the input image signal Da. Is subtracted in accordance with the position of the integer part to calculate a new output image signal Db (step S132 in FIG. 12). That is, the pixel value calculation means 62 subtracts the value of the correction bit data Cd from the gradation value La (x) of the image signal Dd as the calculation processing of the correction bit data Cd with respect to the image signal Dd. Processing equivalent to adding the value of the additional bit E to the lower side is performed (see FIG. 11). When the calculated value is a negative value, the output image signal Db is set to “0” (Db = 0), and the value exceeds the set number of bits (maximum value) of the output image signal Db. The value of the output image signal Db is limited with the value as the maximum value.

  Since the correction bit data Cd includes a decimal part with respect to the gradation value of the image signal Dd (or input image signal Da), the output image signal Db after being processed by the pixel value calculation means 62 is the image signal. A highly accurate image signal having a decimal part with respect to Dd. Since the output image signal Db has the number of bits in the decimal part of the correction bit data Cd including the decimal part, the resolution of the gradation value is increased, and a smoother change in the gradation value can be expressed. When the change in the gradation value is caused by the edge of the image, the correction bit data Cd is obtained as 0. As a result, no gradation is added to the pixel adjacent to the edge portion of the image, and the output image signal While maintaining the outline information of Db, the smoothness of the image can be increased in the pixel region where the gradation value gradually changes other than the edge of the image.

  In FIG. 13 (j) and FIG. 14 (j), the value obtained by adding the correction bit data Cd to the image signal Dd is represented by 1 as the minimum gradation value of the image signal Dd. According to FIG. The gradation value Lb (x) of the output image signal Db after adding the bit data Cd is obtained by subtracting the correction bit data Cd from the gradation value La (x) of the image signal Dd, thereby obtaining the gradation change position signal Pt. = 1/4 at the pixel position x = 8, the gradation value Lb (x) = 4/4, and in the subsequent gradation flat interval, the gradation value from the gradation value at the pixel position x = 8 to the pixel position is 5/4. 6/4, 7/4,..., And so on. Similarly, at the pixel position x = 24, the gradation value Lb (x) of the output image signal Db is 21/7, and in the subsequent gradation flat period, the pixel position is changed from the gradation value at the pixel position x = 24. The gradation values are obtained as gradation values having a change increasing every 1/7, such as 22/7, 23/7, 24/7,.

  Further, according to FIG. 14J, the gradation value Lb (x) of the output image signal Db is the gradation value Lb (x) = 48 / at the pixel position x = 16 of the gradation change position signal Pt = 1. 6 and thereafter, in the gray level flat section, the gray level value decreases from the gray level value at the pixel position x = 16 in units of 1/6, such as 47/6, 46/6, 45/6,. It is obtained as a gradation value having a change. Similarly, at the pixel position x = 24, the gradation value Lb (x) = 49/7 of the output image signal Db, and in the subsequent gradation flat interval, the pixel position is changed from the gradation value at the pixel position x = 24. The tone values are obtained as gradation values having a change that decreases every 1/7, such as 48/7, 47/7, 46/7,. It should be noted that since the correction value aCd (that is, the correction bit data Cd) is 0 at the pixel position x = 8 in FIG. 14J, the pixel position x = 8 and the subsequent gray level flat section (x = 15). No change in gradation value is possible even in the case of the pixel.

  13 (k) and 14 (k) show the output image signal Db when the additional bit E in the correction bit data Cd is 4 bits. According to FIG. 13 (k), the output image signal Db is shown. Is obtained as a gradation value having a change increasing for each value corresponding to the gradient data value Ksl in the order of the pixel position from the pixel position x = 8, 16, 24, 32 where the gradation change position signal Pt = 1. As a result, a 12-bit output image signal Db in which the change in gradation value is converted more smoothly is obtained. Further, also in FIG. 14 (k), the output image signal Db is for each value corresponding to the inclination data value Ksl in the order of the pixel position from the pixel position x = 16, 24, 32 where the gradation change position signal Pt = 1. As a result, a 12-bit output image signal Db is obtained in which the change in gradation value is more smoothly converted.

  1, 11, 13 (a) to (k), and FIGS. 14 (a) to (k), the case where the additional bit E in the correction bit data Cd is generated with 4 bits is shown. However, the present invention is not limited to such an embodiment, and the correction bit data Cd (that is, the correction value aCd) may be expressed by a larger number of bits. In this case, it is possible to obtain an image signal with a more accurate and smoother gradation value change. For example, in FIGS. 13A to 13K, since the inclination data value Ksl is +1/4 from the pixel position x = 8 to the pixel where the next gradation value changes, the absolute value of the correction value aCd Since the change of the value ¼ is indicated, the correction bit data Cd can be expressed without error if the additional bit E is composed of 3 bits. However, after the pixel position x = 24 in FIGS. 13A to 13K, since the inclination data value Ksl is +1/7, the amount of gradation change in the correction value aCd is indicated. Therefore, the corrected bit data Cd can be expressed with a small error.

  In other words, the correction value aCd is obtained from the slope data value Ksl obtained from the amplitude limit gradation change amount Xlm and the flat width data predicted value dst, so The change in the correction value aCd can be made finer by increasing the number of pixels (the number of pixels) and increasing the number of bits representing the inclination data value Ksl. Therefore, when the number of additional bits E in the correction bit data Cd is increased, an image with higher gradation resolution (accuracy) can be obtained.

  At this time, the flat width data predicted value dst is obtained as a value obtained by predicting the flat width after the pixel position where the gradation value changes, and the correction value aCd is sequentially calculated from the pixel where the gradation value changes in the immediately preceding pixel. Since it is obtained by subtraction (pCd−dK) of the correction value aCd and the gradation change amount dK based on the inclination data value Ksl, even when the gradation value changes very slowly, There is no need to hold image signals and correction values for a flat width. Therefore, each time the number of bits constituting the flat width prediction means 20 for obtaining the flat width data predicted value dst and the number of bits representing the slope data value Ksl are increased by 1, the correction value aCd can be expressed with double accuracy. it can. For this reason, for example, the flat width data predicted value dst up to 1023 pixel width is composed of 10 bits, the gradient data value Ksl is obtained with 10 bits, and the additional bit E in the correction bit data Cd is 10 bits. Even when the 8-bit input image signal Da (256-gradation image) is converted to 18-bit (262144-gradation image) data, the number of bits constituting the flat width prediction means 20 and the gradient data value Ksl. Only by increasing the number of bits representing the correction bit data Cd, there is no need to increase the delay means, that is, the data to be held, by the number of pixels corresponding to the increased number of bits. Therefore, according to the first embodiment, the output image signal Db with high accuracy can be obtained even in a pixel region in which the gradation value changes very slowly by real-time processing without greatly increasing the circuit scale. Obtainable.

<< 1-4 >> Effect.
As described above, according to the image processing apparatus of the first embodiment, the image signal for the flat width is processed in real time without being held, and the process is performed very slowly without significantly increasing the circuit scale. Even in a section where the tone value changes or when it is determined that the change in the tone value is caused by the edge of the image, the change in the tone value is detected to obtain appropriate correction bit data Cd, and the tone of the image signal It is possible to obtain a high-quality image signal with a smooth gradation value change in which the number is expanded and quantization noise or pseudo contour is reduced.

  In the above description, the case where the input image signal Da is 8 bits, the additional bit E in the correction bit data Cd is generated by 4 bits, and the number of gradations is extended to the 12-bit output image signal Db is shown. However, the number of gradations of the input image signal Da is not limited to 8 bits, and may be an image signal having a number of gradations other than 8 bits, for example, 10 bits. In this case, a 14-bit output image signal Db is obtained, and a more accurate image signal can be obtained. Even when the number of bits of the correction bit data Cd (that is, the correction value aCd) is increased, the number of bits in the configuration up to the generation of the correction bit data Cd, that is, the flat width data predicted value dst, the inclination data value It can be configured only by increasing the number of bits in Ksl and correction value aCd, and the same effect can be achieved.

  Further, in FIG. 1, when the correction limit coefficient setting means 30 determines that the change in the gradation value is caused by the edge of the image, the correction limit coefficient rc for limiting the correction is set so that the edge of the image is in the vicinity. In the existing pixel (correction limiting coefficient rc = 0), no gradation value is added and the contour information of the image is maintained. However, the gradation change amount limitation in the gradation change detecting means 10 is limited. When the means 12 obtains the amplitude limited gradation change amount Xlm whose value is limited so that the value of the gradation change amount dfx falls within the range from −1 to +1, the value of the gradation change amount dfx is − When the range from 1 to +1 is exceeded, even if the value is set to 0 (that is, the amplitude limit gradation change amount Xlm = 0), similarly, the pixels after the pixel that becomes the edge of the image The correction value aCd at 0 can be made zero. That is, if the amplitude limit gradation change amount Xlm = 0 at a pixel that is an edge of an image where the value of the gradation change amount dfx exceeds the range from −1 to +1, the inclination data value Ksl = 0 and correction is performed. Since the value aCd = (rc) × (Xlm) = 0 can be obtained, the same correction value aCd as when the correction limiting coefficient rc = 0 is obtained. In this case, the correction value is set to 0 only in the gradation flat section after the pixel in which the gradation value changes due to the edge of the image.

<< 1-5 >> Modifications.
In the above description, the gradation conversion means 1 detects the amount of gradation change in the horizontal direction and generates the correction bit data Cd for the gradation value in the change of the gradation value in the horizontal direction of the input image signal Da. In the above description, the correction bit data is added to the image signal to convert the gradation to reduce the quantization noise. However, the amount of gradation change in the vertical direction (screen display scanning line direction) of the input image signal Da is detected. Then, the correction bit data Cd may be generated and added to the image signal to smooth the change in the gradation value in the vertical direction, and the same effect can be obtained. In this case, the gradation change detecting means 10 obtains the gradation change amount dfx based on the difference between the pixels on the upper scanning line located vertically above and below, and the flat width predicting means 20 and the inclination detecting means 40. As a delay process for one pixel of each signal in the correction bit generation means 50 as a delay process for one line (one horizontal scanning period), it is possible to detect a change in gradation value in pixels located vertically above and below, What is necessary is just to comprise so that initialization by the initialization signal Sif from the timing signal production | generation means 100 may be performed for every synchronizing signal (vertical synchronizing signal) of a vertical direction (namely, every frame).

  Further, in the above description, it has been described that each configuration of the gradation converting means 1 in the image processing apparatus is a hardware configuration, but the present invention is configured to be realized by software processing in program control. Also good.

<< 2 >> Embodiment 2
In the first embodiment, the gradation change amount limiting means 12 in the gradation change detection means 10 changes the gradation change amount dfx from −1 to +1 (the lowest 1 of the gradation values of the input image signal Da). The image processing apparatus and the image processing method for limiting the difference to be within the range of the bit difference) have been described. However, the present invention is not limited to such an embodiment. For example, the gradation change amount limiting unit 12 in the gradation change detection unit 10 sets the value of the gradation change amount dfx to a predetermined maximum value (first floor). The present invention can also be applied to an image processing apparatus and an image processing method that limit the range to a predetermined minimum value (a negative value whose absolute value is greater than one gradation) from a positive value greater than the key.

  The image processing apparatus of the second embodiment has the same configuration as the image processing apparatus of FIG. 1 used for the description of the first embodiment. Therefore, FIG. 1 is also referred to in the description of the second embodiment. The image processing apparatus according to the second embodiment performs the difference value of the gradation values used when detecting the change of the gradation value based on the maximum value and the minimum value which are the differences of gradation values larger than one gradation. The configured point is different from the image processing apparatus according to the first embodiment in which the difference value of the gradation value used when detecting the change of the gradation value is set to −1 and +1. Except for this point, the image processing apparatus of the second embodiment is the same as the image processing apparatus of the first embodiment.

  In the image processing apparatus of the second embodiment, the gradation converting means 1 shown in FIG. 1 detects the change in the gradation value of the input image signal Da in the horizontal direction up to the gradation value difference “2”, and the pixel A change within a range from the maximum value +2 to the minimum value −2 of the difference between the gradation values is obtained. Then, for the 8-bit input image signal Da, a correction value (correction bit data) based on an additional bit E of a value indicated by 5 bits by an integer part 1 bit and a decimal part 4 bits is generated and added to the input image signal Da. Then, it is converted into an output image signal Db in which the number of gradations is expanded to 12 bits.

  In FIG. 1, the configuration and operation of the timing signal generation unit 100 and the gradation conversion unit 1 are the same except that the change within the range from the maximum value +2 to the minimum value −2 of the difference in gradation value between pixels is obtained. This is the same as that shown in the first embodiment. Hereinafter, the configuration of the gradation converting means 1 in the second embodiment will be described.

  The gradation change detection means 10 in the gradation conversion means 1 calculates the difference in gradation value between pixels adjacent in the horizontal direction in the input image signal Da to obtain the value of the gradation change amount dfx, and the gradation change The amount dfx is output, and the amplitude limit gradation change amount Xlm in which the value of the gradation change amount dfx is limited to a predetermined range, and whether or not the pixel has a gradation value changed from the value of the gradation change amount dfx. A gradation change position signal Pt indicating the pixel position where the gradation value, which is the detection result, has changed is output.

  The amplitude limit gradation change amount Xlm is obtained by the gradation change amount restriction means 12 in the gradation change detection means 10, and the value is restricted so that the gradation change amount dfx falls within the range of −2 to +2. The The gradation change amount limiting means 12 detects a change of the 8-bit input image signal Da from 2 gradations within a limited range (a range from −2 to +2), and −− as an amplitude limited gradation change amount Xlm. Any one of 2, -1, 0, +1, and +2 is output.

  The gradation change position signal Pt is a value whose absolute value is larger than 0 from the value of the gradation change amount dfx in the gradation change position detection means 13 in the gradation change detection means 10. If the difference is greater than or equal to the key, it is determined that there is a change in gradation value, and Pt = 1. On the other hand, when the gradation change amount dfx is dfx = 0, the gradation change position signal Pt determines that the pixel is flat without changing the gradation value, and Pt = 0. The configuration of the gradation change position detecting means 13 is the same as that of the first embodiment.

  The flat width predicting means 20 uses the pixel position indicated by the gradation change position signal Pt = 1 obtained from the gradation change amount dfx from the gradation change detecting means 10 as a reference position, and a pixel (reference pixel) at this reference position. ) To obtain the number of pixels (flat width) in a flat period (gradation flat section) without change in the gradation value up to the previous pixel, and with respect to the flat width (flat count value) of the gradation flat section up to the previous pixel. Cyclic filter processing is performed to obtain a flat width data predicted value dst that is a value obtained by predicting the flat width of the flat gradation section after the pixel position where the gradation value changes. The flat width predicting means 20 performs such flat width data predicted value dst generation processing every time a pixel whose gradation value changes is detected.

  The correction limiting coefficient setting unit 30 determines whether or not the difference between the gradation values in the pixels adjacent to the edge of the image is due to the edge of the image based on the gradation change amount dfx from the gradation change detection unit 10. From the result, the correction limiting coefficient rc is set as a value that can limit the correction value so that the gradation correction value is not added to the edge of the image. For example, the correction limit coefficient rc is a predetermined value TH to be compared with the maximum difference absolute value dfm obtained from the absolute value of the gradation change amount dfx by the correction limit coefficient setting unit 30 as shown in FIG. By setting the value to 2, a value in the range from 0 to 1 is obtained so as to obtain the characteristics shown in FIG. When the maximum difference absolute value dfm increases, the value of the correction limiting coefficient rc approaches 0, and it is determined that the change in gradation value is due to the edge of the image, and the correction value is limited so that the number of gradations is not expanded. On the other hand, when the value of the maximum difference absolute value dfm is equal to or smaller than the threshold value TH = 2, the correction limiting coefficient rc = 1, and the gradation change of the direct input image signal Da is a gradual range from +2 to −2. Therefore, it can be determined that the number of gradations is extended.

  The inclination detection means 40 detects the horizontal direction of the input image signal Da from the amplitude limit gradation change amount Xlm and the flat width data predicted value dst at the pixel position where the gradation value indicated by the gradation change position signal Pt = 1 changes. Is detected, and the inclination data value Ksl is obtained. Since the amplitude limit gradation change amount Xlm is input as a value in which the gradation change amount dfx is limited within the range of −2 to +2, the gradient of the detected gradation value also ranges from −2 to +2. It becomes a value limited by the value in.

  The correction bit generation means 50 obtains the inclination data value Ksl from the inclination detection means 40 as the gradation change amount dK for each adjacent pixel of the correction value (dK = Ksl), and changes the gradation according to the gradation change position signal Pt. A correction value aCd to be added to the input image signal (pixel data) Da is obtained from the amount dK, the amplitude limit gradation change amount Xlm, and the correction limit coefficient rc, and the correction value aCd is determined as the gradation value of the input image signal Da. Correction bit data Cd is generated as a bit string including an additional bit E including a fractional part and a sign bit of the value to be added, and is output to the pixel value calculation means 62. With the configuration of the correction bit generation means 50 shown in FIG. 10, the correction value aCd to be added to the input image signal Da is a value (rc) × (Xlm) based on the amplitude limit gradation change amount Xlm and the correction limit coefficient rc. From this value, it is obtained as a value that sequentially changes to 0 by the difference of the gradation value by the inclination data value Ksl in order of the pixel, and becomes a gradation value having a decimal part precision.

  Here, in the case where the additional bit E in the correction bit data Cd is generated with 5 bits of an integer part 1 bit and a decimal part 4 bits and added to the input image signal Da, for example, the absolute value of the correction value aCd excluding the sign Is converted to a 5-bit bit string value. At this time, the value that becomes the integer part 2 of −2 and +2 is 32 in the bit string. Therefore, this value is limited to 5 bits, and the value in the bit string is obtained as 31, and the correction value aCd Is a bit string value having a predetermined number of bits. The correction bit data Cd is a bit string of the converted 5-bit additional bit E together with a sign bit (having a bit number of 1 bit or more) indicating the sign of the correction value aCd.

  The pixel value calculation unit 62 subtracts the correction bit data Cd from the correction bit generation unit 50 from the gradation value of the delay-compensated image signal Dd from the delay compensation unit 61 by matching the position of the integer part. To calculate and output a new output image signal Db.

  15 shows the input image signal Da (or the delay compensated image signal Dd from the delay compensation means 61), the correction bit data Cd from the correction bit generation means 50, and the pixel value calculation means 62 in the second embodiment. It is a figure which shows the relationship of the output image signal Db output. Here, the input image signal Da (or image signal Dd) is m = 8 bits, the correction bit data Cd is a sign bit and an additional bit E (5 bits), and the output image signal Db is n = 12 bits. . When the correction bit data Cd is composed of a sign bit and an additional bit E (5 bits), the value is limited so that the gradation change amount dfx is in a range from −2 to +2, and therefore the additional bit E is The image signal Dd is composed of a 1-bit integer part and a 4-bit decimal part.

  As shown in FIG. 15, the pixel value calculation means 62 matches the position of the integer part in the additional bit E in the correction bit data Cd with the position of the integer part of the image signal Dd (the least significant bit corresponds to the integer 1). The output image signal Db is calculated by subtracting or adding the value thus made to the image signal Dd according to the sign. The output image signal Db has a bit string extending downward by the number of bits indicating the decimal part relative to the image signal Dd, that is, the output image signal Db includes a decimal part with respect to the gradation value of the original input image signal Da. The resolution of one gradation of the signal Db is higher than that of the image signal Dd, quantization noise or pseudo contour is further reduced, and an accurate gradation can be expressed.

  With the above configuration, not only the change in the gradation value of one gradation which is the minimum gradation value of the input image signal Da but also the quantization noise (for example, one gradation or more in the input image signal Da). Even if it is included due to gradation jumps), it is not necessary to hold the image signal for the flat width when the gradation value changes, and the gradation value is gradually increased without significantly increasing the circuit scale. 12-bit output in which gradation value changes are obtained more smoothly by obtaining appropriate correction bit data Cd when it is determined that the change in gradation value is caused by the edge of the image. An image signal Db is obtained.

  The operation of the gradation conversion means 1 in the image processing apparatus according to the second embodiment is to obtain a change within the range from the maximum value +2 to the minimum value −2 of the difference in gradation value between pixels. Is the same as the flowchart for explaining the operation of the gradation converting means 1 in the image processing apparatus according to the first embodiment shown in FIG. However, in the second embodiment, the limit range of the gradation change amount dfx in step S103 in FIG. 12 is set to a range between the maximum value +2 and the minimum value −2 (TH = 2 in FIG. 12). The correction value aCd obtained in S114 and S122 is a value including a decimal number whose absolute value in the range from −2 to +2 is 2 or less.

FIGS. 16A to 16L are diagrams for explaining the operation in the gradation converting means 1 when the limited range of the gradation change amount dfx is in the range from −2 to +2. 4A is a horizontal pixel position x of the input image signal Da, FIG. 4B is the input image signal Da, and FIGS. The gradation change amount dfx due to the difference in gradation value between pixels, the amplitude-limited gradation change amount Xlm of the gradation change amount dfx, and the gradation change position signal Pt, FIG. The flat width count value Cnt which is an output from the flat width count means 21, and (g) in the figure shows the flat width data predicted value dst in which the flat width output from the cyclic filter processing means 22 in the flat width prediction means 20 is predicted. (H) in the figure shows the inclination data value Ksl output from the inclination detecting means 40, (i) in FIG. 11 shows the correction limiting coefficient rc output from the correction limiting coefficient setting means 30, and (j) in FIG. Correction value aCd obtained in the means 50, FIG. 7 (k) shows the gradation when the value obtained by adding the correction bit data Cd to the image signal Dd (that is, the input image signal Da) in the pixel value calculation means 62 is represented by 1 as the minimum gradation value of the image signal Dd. (L) in the figure shows the output image signal Db which is the output of the pixel value calculation means 62, and shows the case where the additional bit E in the correction bit data Cd is 5 bits. In FIGS. 16A to 16L, pixel data is input in order from the left, and the horizontal axis indicates the pixel position in the horizontal scanning direction. 16 (a) is aligned four pixels pixel gradation value La (x) = 4 is in order from the pixel position _{x 1,} the gradation value La (x) = 6 pixels 4 pixels aligned from the pixel position _{x 2} in order , the pixel of the gradation value La (x) = 9 in this order from the pixel position _{x 3} is aligned 5 pixels, the pixel of the gradation value La (x) = 13 from the pixel position _{x 4} in the order indicates the image along with three pixels .

When the input image signal Da (referred to as gradation value La (x)) shown in FIG. 16B is input to the gradation conversion means 1, the gradation change amount dfx shown in FIG.
dfx = La (x) −La (x−1)
Is calculated by In FIG. 16 (c), dfx = + 1, the pixel position _{x 2} is dfx = + 2, the pixel position _{x 3} is dfx = + 3, the pixel position _{x 4} at the pixel position _{x 1} becomes dfx = + 4. The amplitude limit gradation change amount Xlm is obtained by limiting the value of the gradation change amount dfx so that it falls within the range from −2 to +2, and is as shown in FIG. In FIG. 16 (d), the amplitude limit gradation change amount XLM = + 1 next to the certain gradation variation dfx = + 1 at the pixel position _{x 1,} whereas the gradation variation in the pixel position _{x 2,} x 3, _{x 4} Since dfx ≧ + 2, the value is limited to the amplitude limit gradation change amount Xlm = + 2, and the amplitude limit gradation change amount Xlm = 0 in the gradation flat section in which there is no gradation change and the gradation value is flat. ing.

  The gradation change position signal Pt shown in FIG. 16 (e), the flat width count value Cnt shown in FIG. 16 (f), and the flat width data predicted value dst shown in FIG. 16 (g) are the same as those in the first embodiment. It is required in the same way as the case.

The inclination data value Ksl shown in FIG. 16H is obtained from the value of the amplitude limit gradation change amount Xlm and the flat width data predicted value dst in the inclination detection means 40 for each gradation change position signal Pt = 1. The following formula Ksl = Xlm / dst
And obtained as a result of detecting the gradient of the horizontal gradation value of the input image signal Da. According to FIG. 16 (h), in the tone changed pixel position _{x 1,} the gradient data value Ksl = + 1/3, and the at pixel position _x 2, _{x 3,} inclination data value Ksl = + 2/3, and the pixel position in x _4, the inclination data value Ksl = + 2/4. Further, as shown in FIG. 16 (h), the values at the pixel positions x ₁ , x ₂ , x ₃ , x ₄ are held in the gradation flat section (Pt = 0).

The correction restriction coefficient rc shown in FIG. 16 (i) is obtained by the correction restriction coefficient setting means 30 from the absolute value of the gradation change amount dfx, for example, with the characteristics shown in FIG. x _{1, x 2} is the correction limit coefficient rc = 1 in, since the gradation variation dfx = + 3 at the pixel position _{x 3,} the correction limit coefficient rc at this position rc = 1/2, and the pixel position x ₄ , the gradation change amount dfx = + 4, and the correction limiting coefficient rc is rc = 0.

  The correction value aCd (correction bit data Cd) to be added to the input image signal Da is changed by the correction bit generation means 50 from the gradient data value Ksl, the amplitude limit gradation change amount Xlm, and the correction limit coefficient rc. It is obtained as a correction value aCd = (rc) × (Xlm) with the position signal Pt = 1, and in the gradation flat section (Pt = 0), the gradient data value Ksl is used in order from the value at the pixel position where the gradation value changes. It is obtained as a value that sequentially changes to 0 due to the difference in gradation value, as shown in FIG. Since both the correction value by the multiplication result (rc) × (Xlm) and the slope data value Ksl are expressed as values having a fractional part with an absolute value in the range from −2 to +2 being 2 or less, the correction value aCd Also, the gradation value has a decimal precision of 2 or less.

In FIG. 16 (k), the value obtained by adding the correction bit data Cd to the image signal Dd is represented by 1 as the minimum gradation value of the image signal Dd, and the gradation of the output image signal Db after the correction bit data Cd is added. value Lb (x), by subtracting the correction bit data Cd from the gradation value La of the image signal Dd, a gray level value of Lb (x) = 9/3 in the pixel position _{x 1,} the subsequent tone flat In the interval, in the order of the pixel position, it is obtained as a gradation value having a change increasing every 1/3, such as 10/3, 11/3,. Similarly, the pixel position _{x 2,} the gradation value Lb (x) = 3/12 of the output image signal Db, the subsequent tone flat sections, in the order of pixels, 14 / 3,16 / 3, ... that Thus, it is obtained as a gradation value having a change that increases every 2/3.

FIG. 16 (l) shows the output image signal Db when the additional bit E in the correction bit data Cd is 5 bits, and the output image signal Db is from the pixel positions x ₁ and x ₂ to the pixel position. Are obtained as gradation values having a change increasing for each value corresponding to the inclination data value Ksl, and as a result, a 12-bit output image signal Db in which the change in gradation value is converted more smoothly is obtained. ing. The correction in the limited pixel position _{x 4} coefficient rc is the image of the edge rc = 0, the correction value ACD = 0 (FIG. 16 (i) and (j)), and the correction to the gradation value of the image signal Dd No value is added.

  In the above description, FIGS. 16A to 16L show the case where the change in the range from the maximum value +2 to the minimum value −2 of the difference in gradation value between pixels is obtained. The invention is not limited to such an embodiment, and other values may be selected as the maximum value and the minimum value. The absolute value of the maximum value (positive value) and the minimum value (negative value) may be different.

  For example, it may be within a range from the maximum value +4 to the minimum value −4. In this case, the number of bits of the integer part of the additional bit E increases. In FIG. 15, if the decimal part remains 4 bits, the additional bit E in the correction bit data Cd is 6 bits. The image signal Dd can be composed of a 2-bit integer part and a 4-bit decimal part. Then, the pixel value calculation means 62 sets a value obtained by matching the position of the integer part in the additional bit E in the correction bit data Cd with the position of the integer part of the image signal Dd (the lower 2 bits correspond to the integer 1). An output image signal Db is calculated by performing an arithmetic process for subtracting or adding the image signal Dd according to the sign.

  Further, although the decimal part of the additional bit E in the correction bit data Cd is 4 bits, it may be other than 4 bits. By expressing the correction value aCd), it is possible to obtain an image signal with a more accurate and smoother gradation value change.

  As described above, according to the image processing apparatus of the second embodiment, the gradation change detecting means 10 can determine in advance the value of the gradation change amount dfx based on the difference in gradation values between adjacent pixels of the input image signal Da. The amplitude limit gradation change amount Xlm is limited within the range of +2 to −2 that is the maximum value (positive value) and the minimum value (negative value), and is flat with the amplitude limit gradation change amount Xlm. An inclination data value Ksl indicating the inclination of the gradation value is obtained from the width data predicted value dst, and correction is performed when the gradation value changes within the difference of the gradation value within the range from +2 to −2. The bit value Cd is generated, and the gradation value is converted by adding the bit by subtracting or adding the value of the correction bit data by aligning the position of the integer part from the input image signal Da in the pixel value calculation means 62. An image signal with an expanded number of bits is obtained. Accordingly, not only the pixel area where the gradation value changes continuously and gradually by the change of the gradation value of one gradation, which is the minimum gradation value of the input image signal Da, but also the first floor of the input image signal Da. Even in the case where quantization noise due to gray level jumps or more is included, the width of the gray level flat section as the flat width data predicted value dst, which is a predicted flat width value, without significantly increasing the circuit scale Then, the inclination data value Ksl is obtained, and a correction value that sequentially changes with the gradation value based on the inclination data value Ksl is obtained. If it is determined that the change in the gradation value is due to the edge of the image, the gradation value is It is not added and can be obtained as a correction value that preserves the contour information of the image. For this reason, according to the image processing apparatus of the second embodiment, the correction signal data Cd is obtained in real time without holding the image signal corresponding to the flat width, and the correction bit data Cd is obtained without significantly increasing the circuit scale. In addition, the number of gradations of the image signal can be expanded to obtain a high-quality image signal with a smooth gradation value change in which quantization noise or pseudo contour is reduced.

  In the above description, the case where the number of gradations of the input image signal Da is 8 bits has been described. However, the number of gradations of the input image signal Da may be other than 8 bits, for example, 10 bits. . Also in this case, if the pixel value calculation means 62 is configured to calculate a value in which the position of the integer part of the additional bit E in the correction bit data Cd matches the position of the integer part of the image signal Dd. The same effect can be produced.

  In the above description, the amount of change in gradation in the horizontal direction is detected to generate correction bit data Cd for the gradation value, and gradation conversion is performed by adding the correction bit data to the image signal to reduce quantization noise. Although described as a configuration to reduce, the gradation change amount in the vertical direction of the input image signal Da is detected, the correction bit data Cd is generated and added to the image signal, and the change in the gradation value in the vertical direction is smooth. It is good.

  In the second embodiment, points other than those described above are the same as those in the first embodiment.

<< 3 >> Embodiment 3
The image processing apparatus according to the third embodiment detects a region of a pixel in which the gradation value monotonously increases or decreases and the gradation value continuously changes, and the gradation value is detected for such a region. Is different from the image processing apparatus according to the first or second embodiment in that it is configured not to convert (the number of gradations is not expanded). Hereinafter, the difference will be mainly described.

  FIG. 17 is a block diagram schematically showing a configuration of an image processing apparatus according to the third embodiment of the present invention (that is, an apparatus capable of performing the image processing method according to the third embodiment). In FIG. 17, the same reference numerals are given to the same or corresponding components as those of the image processing apparatus shown in FIG. Similar to the image processing apparatuses according to the first and second embodiments, the image processing apparatus according to the third embodiment detects a change in gradation value in a certain direction (for example, the horizontal direction) of the screen, and the gradient of the gradation value. , And a correction value is calculated using this inclination, and a gradation conversion process for expanding the number of bits of the input image signal Da is performed using this correction value. However, in the image processing apparatus according to the third embodiment, the gradation value is monotonously increased or decreased in a pixel region where the gradation value continuously changes (hereinafter also referred to as “continuous change”). It is configured not to perform the number expansion process.

  In FIG. 17, the image processing apparatus according to the third embodiment performs gradation conversion processing for extending the number of bits by adding lower bits to an m-bit digital input image signal Da, and outputs an n-bit output image. Output as signal Db. As shown in FIG. 17, the image processing apparatus according to the third embodiment includes a timing signal generation unit 100 and a gradation conversion unit 2. In addition to the configuration of the gradation conversion unit 1 shown in FIG. 1, the gradation conversion unit 2 includes a continuous change determination unit 70 that determines a continuously changing pixel region in which the gradation value continuously changes for each pixel. Yes. In the third embodiment, the correction bit data is also referred to by referring to the continuous result determination result sqf from the continuous change determination means 70 instead of the correction bit generation means 50 in the gradation conversion means 1 shown in FIG. Correction bit generation means 50b configured to generate Cd is provided. The image processing apparatus according to the third embodiment, except that the continuous change determination unit 70 is provided and the correction bit generation unit 50b generates the correction bit data Cd with reference to the continuous result determination result sqf. This is the same as the image processing apparatus of the first or second embodiment.

  As in the image processing apparatus shown in FIG. 1, the image processing apparatus shown in FIG. 17 obtains a change in the gradation value difference between pixels from +1 to −1 with respect to the horizontal direction of the input image signal Da. The gradation change amount is detected, gradation conversion processing for expanding the number of gradations of the 8-bit input image signal Da is performed, and the result is output as a 12-bit output image signal Db.

  The timing signal generation unit 100 generates an initialization signal Sif for initialization for each horizontal synchronization signal, and the gradation conversion unit 2 receives the input image signal Da and the initialization signal Sif. The gradation converting means 2 performs gradation conversion by expanding the number of bits by adding correction bit data Cd which is a correction value for 4 bits to the 8-bit input image signal Da, for example. , And output as a 12-bit output image signal Db. The correction bit data Cd in the gradation converting means 2 is a flat image obtained by predicting a gradation change amount obtained from a difference in gradation values between pixels of the input image signal Da and a flat width obtained based on the gradation change amount. It is generated by obtaining the gradient of the gradation value from the width data predicted value, and also according to the result sqf of determining the region of the pixel that is continuously changed in the continuous change determining means 70 in the gradation converting means 2. The correction bit data is generated.

  Hereinafter, the configuration of the gradation converting means 2 will be described. The configurations of the gradation change detection means 10, the flat width prediction means 20, the inclination detection means 40, and the correction limit coefficient setting means 30 in the gradation conversion means 2 are the same as those in the first embodiment (FIG. 1). is there.

  The continuous change determination means 70 in the gradation conversion means 2 receives the gradation change amount dfx from the gradation change detection means 10. The continuous change determination means 70 determines a region of a pixel in which the gradation value monotonously increases or decreases from the value of the gradation change amount dfx and becomes a continuous change, and a continuous change determination result sqf indicating a pixel in which the continuous change occurs. And the generated continuous change determination result sqf is output to the correction bit generation means 50b.

FIGS. 18A and 18B are examples of changes in the pixel position and the gradation value La (x) in the pixel area where the gradation value monotonously increases or decreases in the input image signal Da and becomes a continuous change. Indicates. In FIGS. 18A and 18B, the horizontal axis indicates the pixel position in the horizontal direction, and the vertical axis indicates the gradation value La (x) of the input image signal Da at each pixel position. In FIG. 18A, the gradation value continuously increases by one gradation at the pixel positions x ₁ and x ₁ +1, and FIG. 18B shows one gradation at the pixel positions x ₁ and x ₁ +1. It shows a case where the gradation value continuously decreases. In FIG. 18 (a) and (b) are respectively the gray scale value by the difference between the one gradation in the horizontal pixel position x ₁ and x ₁ +1 is changed continuously.

In each of adjacent adjacent pixels as shown in FIGS. 18A and 18B, when the gradation value increases or decreases by one gradation, the difference in gradation value for each pixel is one gradation. the case, for example, in FIG. 18 (a) and (b) a pixel position x ₁ in, the difference in gray scale value between adjacent pixels before and after is 2 gradations, flat at the pixel position x ₁ and later Therefore, there is no problem even when a contour is seen at the boundary described above, because the gradation value of the signal is not a smooth change at the boundary between adjacent pixels. In addition, if the process of extending the number of gradations is performed on pixels that have already changed continuously, the change may not be continuous, and contour information due to the change may be lost.

In addition, even when there is a change in gradation value for every two pixels as shown in FIGS. 19A and 19B, it can be determined that the region of the pixel is a continuous change. FIGS. 19A and 19B show another example of the change in the pixel position and the gradation value La (x) in the region of the pixel that is continuously changed in the input image signal Da, which is the same as FIG. The horizontal axis indicates the pixel position in the horizontal direction, and the vertical axis indicates the gradation value La (x) of the input image signal Da at each pixel position. In FIG. 19A, one gradation is increased at adjacent pixels x ₁ −1 and x ₁ +1 before and after the pixel position x ₁ , and FIG. 19B is obtained at pixel positions x ₁ −1 and x ₁ +1. The figure shows a case where one gradation is decreased, and it continuously changes with a difference of one gradation in the width of two pixels.

In the cases shown in FIGS. 19A and 19B, the pixel having no gradation change is only the pixel position x ₁ between the pixel positions x ₁ −1 and x ₁ +1 where the gradation value changes. since, at the boundary between the adjacent pixels at the pixel position x _1, it can not be said that the gradation value of the signal is changing smoothly, there is no problem even if the contour is looked above the boundary, the pixel position x ₁ will be the value of the gradation change at the pixel position x ₁ is performed a process of expanding the number of gradations, there is a case where the contour information is lost.

  Therefore, the continuous change as shown in FIGS. 18A and 18B and FIGS. 19A and 19B is obtained from the magnitude of the gradation change amount dfx at the target pixel position and the adjacent pixel positions. The pixel region is determined, and from the result, the correction value is generated so that the gradation correction value is not added to the pixel in the pixel region that is continuously changed. sqf is generated.

The continuous change determination means 70 first has a pixel position x ₁ and adjacent pixels x ₁ -1 and x ₁ +1 located before and after the target pixel position x ₁ with respect to the gradation change amount dfx from the gradation change detection means 10 due to pixel delay or the like. The gradation change amount dfx is obtained, and it is determined from the relationship between the magnitude of the obtained gradation change amount dfx and the sign thereof whether or not the pixel region is a continuous change. Here, it represents a dfx (x) the gradation variation at the pixel position x, the gradation change amount at the target pixel position _{x 1} represents the dfx _{(x 1),} the gradation variation at the pixel position _x 1 -1 It is expressed as dfx (x ₁ −1), and the gradation change amount at the pixel position x ₁ +1 is expressed as dfx (x ₁ +1).

The gradation change amount dfx at each pixel position is 0 in the gradation flat section where the gradation value does not change, and in the pixel where the gradation value has changed, the absolute value is expressed as a difference in gradation value. The direction of change (increase or decrease) of the tone value is obtained as the sign of the gradation change amount dfx (the gradation change amount dfx> 0 when the gradation is increased, and the gradation change amount dfx <0 when the gradation is decreased). ing. Therefore, the gradation change amount dfx (x ₁ ), the gradation change amount dfx (x ₁ −1), and the gradation change amount dfx (x ₁ +1) are obtained at the target pixel position x ₁ and adjacent pixels located before and after the target pixel position x _1. after, if then meets the condition 1 or condition 2 shown determines that a pixel in the region of the pixel to which the pixel of interest position x ₁ is the continuous variation.

(Condition 1), either of the pixels adjacent to the target pixel position x ₁ in front or after, when the difference between one or more changes in the same direction of the gradation values are consecutive (Fig 18 (a) and ( b), the gradation change amount dfx (x ₁ ) ≠ 0, the gradation change amount dfx (x ₁ −1) ≠ 0, and dfx (x ₁ ) and dfx (x ₁ − 1) have the same sign, or gradation change amount dfx (x ₁ ) ≠ 0, gradation change amount dfx (x ₁ +1) ≠ 0, and dfx (x ₁ ) and dfx ( x ₁ +1) have the same sign)
(Condition 2) is a case where two pixels adjacent before and after the target pixel position x ₁ continue to change in the same direction with a gradation value difference of 1 or more (as shown in FIGS. 19A and 19B). When the gradation change amount dfx (x ₁ −1)> 0 and the gradation change amount dfx (x ₁ +1)> 0, or the gradation change amount dfx (x ₁ −1) <0 and the gradation change amount dfx (When x ₁ +1) <0).
The determination of the region of the pixel that is continuously changed to meet the condition 1 or 2 is performed by the gradation change amount dfx (x ₁ ), the gradation change amount dfx (x ₁ −1), and the gradation change amount dfx (x ₁ From (+1), for example, a continuous change determination result sqf indicating a pixel that is continuously changed is generated by the configuration shown in FIG.

  FIG. 20 is a block diagram schematically showing an example of the configuration of the continuous change determination means 70. The continuous change determining means 70 combines the results of the condition 1 determining means 71 and 72, the condition 1 combining means 73, the condition 2 determining means 74, the condition 1 combining means 73 and the condition 2 determining means 74, and continuously. It is comprised from the synthetic | combination means 75 which produces | generates and outputs as a change determination result sqf. The condition 1 determination means 71 and 72 have the same configuration with only different inputs.

In FIG. 20, the condition 1 determination means 71 and 72 in the continuous change determination means 70 include a gradation change amount dfx (x ₁ ), a gradation change amount dfx (x ₁ −1), or a gradation change amount dfx (x ₁ + 1) is input. The condition 1 determination means 71 and 72 have the same configuration except for the input of the gradation change amount dfx (x ₁ −1) or the gradation change amount dfx (x ₁ +1), and the target pixel position x ₁ Is a region of pixels that are continuously changed to meet the above condition 1.

Condition 1 determining means 71, the gradation from the gradation variation dfx _{(x 1)} and tone variation dfx _(x 1 -1), at the pixel position _x 1 -1 adjacent to the pixel position _{x 1} is the condition 1 It is a continuous change that is a change in the same direction in which the value difference increases or decreases by 1 or more, that is, the gradation change amount dfx (x ₁ ) ≠ 0 and the gradation change amount dfx (x ₁ − 1) it is determined if not 0 at the same reference numerals, as a determination result at the pixel position x _1, obtains the determination results pf1 showing a binarized value. The value of the determination result pf1 is, for example, a value “1” (pf1 = 1) when the condition 1 is satisfied, and a value “0” (pf1 = 0) when the condition is not satisfied. Note that the value of the determination result pf1 is not limited to this, and may be another value as long as the pixel position is a continuous change that meets the condition 1.

Similarly, condition 1 determining section 72, floor from the tone variation dfx _{(x 1)} and tone variation dfx _(x 1 +1), the pixel position _x 1 +1 and an adjacent pixel position _{x 1} is the condition 1 determining whether the continuous change having the same direction of the change in the difference between one or more increase or decrease in tone value, as the determination result at the pixel position x _1, obtains the determination results pf2 showing a binarized value. The value of the determination result pf2 is obtained in the same manner as the determination result pf1 in the condition 1 determination means 71.

When the determination results pf1 and pf2 from the condition 1 determination means 71 and 72 are input to the condition 1 combining means 73, the condition 1 combining means 73 combines the determination results pf1 and pf2 to obtain the condition 1 determination result sq1. The condition 1 combining unit 73 is configured by, for example, an OR gate, and obtains the condition 1 determination result sq1 = 1 when the determination result pf1 = 1 or the determination result pf2 = 1. Results As a result, the pixel position x _1, there is a continuous change meets the condition 1 in any of the pixels adjacent to the front or rear, is determined to be in the region of the pixel to which the pixel of interest position x ₁ is continuously changed Is obtained.

When the gradation change amount dfx (x ₁ −1) and the gradation change amount dfx (x ₁ +1) are input to the condition 2 determination unit 74 in the continuous change determination unit 70, the condition 2 determination unit 74 determines whether the target pixel position x ₁ determines whether a region of pixels to be compatible with the continuous change in the condition 2. Condition 2 judging means 74, the gradation variation dfx _(x 1 -1) and the gradation change amount dfx from _(x 1 +1), the pixel position _{x 1} adjacent to the front and rear of the target pixel position _{x 1} is condition 2 - 1 and x ₁ +1, the difference in gradation value is a continuous change that is an increase or decrease in the same direction increasing or decreasing by 1, that is, the gradation change amount dfx (x ₁ −1)> 0 and the gradation change It is determined whether the amount dfx (x ₁ +1)> 0 or the gradation change amount dfx (x ₁ −1) <0 and the gradation change amount dfx (x ₁ +1) <0, and the pixel position x ₁ As a determination result, a condition 2 determination result sq2 indicating a binarized value is obtained. The value of the condition 2 determination result sq2 is, for example, the value “1” (sq2 = 1) when the condition 2 is satisfied, and the value “0” (sq2 = 0) when the condition 2 is not satisfied. ). Note that the value of the condition 2 determination result sq2 is not limited to this, and may be any other value as long as the pixel position is a continuous change that conforms to the condition 2.

When the condition 1 determination result sq1 by the condition 1 combining unit 73 and the condition 2 determination result sq2 by the condition 2 determining unit 74 are input to the combining unit 75, the combining unit 75 may determine whether the condition 1 or the condition 2 is met. Then, a continuous change determination result sqf indicating a pixel in a pixel region where the gradation value monotonously increases or decreases and becomes a continuous change is generated and output. That is, the synthesizing unit 75 combines the condition 1 determination result sq1 and the condition 2 determination result sq2, and is configured by an OR gate, for example, so that the condition 1 determination result sq1 = 1 or the condition 2 determination result sq2 = 1. In addition, the continuous change determination result sqf = 1 is set, and in other cases, the continuous change determination result sqf = 0 is output. Thus, at pixel position x ₁ that is determined to meet the condition 1 or condition 2, the continuous change determination result sqf = 1 becomes as sqf = 0 continuously change determination result if not fit the other, pixels to be continuously changed Is shown. Note that the value of the continuous change determination result sqf is not limited to this, and may be any other value as long as the pixel position is a continuous change that conforms to Condition 1 or Condition 2.

For example, in the case where each adjacent continuous pixel in FIG. 18A increases by one gradation, the gradation change amount dfx (x ₁ ) = + 1> 0 at the pixel position x ₁ and the adjacent pixel position. since in x ₁ gradation change in +1 amount _{dfx (x 1 +1) = +} 1> 0, complies with the condition 1, the judgment result pf2 = 1 from condition 1 determining section 72 in FIG. 20, condition 1 synthesis The condition 1 determination result sq1 = 1 from the means 73 is obtained. Therefore, the continuous change determination result sqf = 1 output from the synthesizing unit 75 is obtained, and the gradation value monotonously increases, resulting in a pixel region that is determined to be continuously changed. Similarly, if in FIG. 18 (b), the gradation change amount dfx at the pixel position _{x 1 (x 1) = -} 1 < 0, the adjacent gradation variation at the pixel position _x 1 +1 for dfx (x _{Since 1} + 1) = − 1 <0, the condition 1 is satisfied, the continuous change determination result sqf = 1, the gradation value monotonously decreases, and the result is determined to be a pixel region that continuously changes. It becomes. It should be noted that the pixel position x ₁ +1 in FIGS. 18A and 18B also conforms to the condition 1, and therefore, similarly to the pixel position x ₁ , the pixel region that undergoes the continuous change with the continuous change determination result sqf = 1. The result determined to be obtained.

Also, in the case where the gradation value changes in FIG. 19A every two pixels, the gradation change amount dfx (x ₁ −1) = + 1> in the pixel x ₁ −1 adjacent to the pixel position x _1. Since the gradation change amount dfx (x ₁ +1) = + 1> 0 at 0, the pixel position x ₁ +1, the condition 2 is satisfied, and the condition 2 determination result sq2 from the condition 2 determination unit 74 in FIG. 1 Accordingly, the continuous change determination result sqf = 1 output from the synthesizing unit 75 is obtained, which is obtained as a result of determining that the pixel region has a continuous change. Similarly, if in FIG. 19 (b), the gradation change amount _dfx (x 1 -1) in the pixel _{x 1 -1 = - 1 <0} , the gradation variation dfx at the pixel position _x 1 +1 _(x 1 +1 ) = − 1 <0, the condition 2 is satisfied, and the continuous change determination result sqf = 1 is obtained, which is obtained as a result of determining that the pixel area is continuously changed.

As described above, the continuous change determination unit 70 changes from the gradation change amount dfx (x ₁ ), the gradation change amount dfx (x ₁ −1), and the gradation change amount dfx (x ₁ +1) to Condition 1 or Condition 2. compatible, it is determined whether the pixel in the region of the pixel to which the pixel of interest position x ₁ is continuously changed, as a result, it is possible to obtain a continuous change determination result sqf.

  It has been described that the continuous change determination unit 70 is configured to determine whether or not the pixel region is subject to continuous change based on the relationship between the magnitude of the gradation change amount dfx and its sign, and obtain the continuous change determination result sqf. However, the amplitude limit gradation change amount Xlm by the gradation change amount limiting means 12 in the gradation change detection means 10 is obtained by limiting the value of the gradation change amount dfx to a predetermined range (range from −1 to +1). Since it is obtained as -1, 0, +1, it can be handled in the same manner as the gradation change amount dfx, and this amplitude limited gradation change amount Xlm may be input to the continuous change determination means 70. The configuration can be the same as in FIG.

  Next, the correction bit generation means 50b in the gradation conversion means 2 of FIG. 17 includes the inclination data value Ksl from the inclination detection means 40, the initialization signal Sif from the timing signal generation means 100, and the gradation change detection means. 10 is input with the gradation change position signal Pt, the amplitude limit gradation change amount Xlm from the correction limit coefficient setting unit 30, and the continuous change determination result from the continuous change determination unit 70. sqf is input. Similarly to the correction bit generation unit 50 of the first embodiment shown in FIG. 1, the correction bit generation unit 50b uses the gradient data value Ksl from the gradient detection unit 40 as the gradation change amount dK for each adjacent pixel of the correction value. (DK = Ksl) is initialized for each horizontal scanning period by the initialization signal Sif, and the gradation change amount dK (that is, the inclination data value Ksl) and the amplitude limit are determined according to the gradation change position signal Pt. A correction value aCd to be added to the pixel signal Da is obtained from the gradation change amount Xlm and the correction limiting coefficient rc, and the correction value is an additional bit E based on a value including a decimal part of the gradation value of the input image signal Da; The correction bit data Cd is generated as a bit string including the sign bit of the value to be added. In addition, when determining the correction value aCd, the continuous change determination from the continuous change determination means 70 is performed. The result sqf, the pixels in the region of pixels to be continuously changed, configured to generate a zero correction value aCd as correction values of the gradation is not added.

  The correction bit generation means 50b can be configured as shown in FIG. 21, for example. FIG. 21 is a block diagram schematically showing an example of the configuration of the correction bit generation means 50b. In FIG. 21, the same reference numerals are given to the same or corresponding components as those of the correction bit generating means 50 in the first embodiment shown in FIG. In FIG. 21, the correction bit generation unit 50 b is a switching unit configured to switch the output value of the switching unit 53 in the correction bit generation unit 50 in FIG. The configuration and operation other than the switching means 56 are the same as those in FIG.

In FIG. 21, the calculation means 51 in the correction bit generation means 50b calculates a correction value based on the amplitude limit gradation change amount Xlm and the correction limit coefficient rc as follows: mCd = (rc) × (Xlm)
Calculate with The subtraction means 52 sets the gradient data value Ksl as the gradation change amount dK for each adjacent pixel of the correction value (dK = Ksl), and calculates the gradation change amount dK from the correction value (delay correction value pCd) in the immediately preceding pixel. Subtraction (pCd-dK) is performed to obtain a correction value sCd in the flat gradation range. The configuration so far is the same as the configuration in FIG.

  An initialization signal Sif, a gradation change position signal Pt, a correction value mCd from the calculation unit 51, and a correction value sCd from the subtraction unit 52 are input to the switching unit 56 in the correction bit generation unit 50b, and continuous change determination is performed. The continuous change determination result sqf from the means 70 is also input. Based on the initialization signal Sif, the gradation change position signal Pt, and the continuous change determination result sqf, the switching unit 56 initializes or resets the correction value mCd from the calculation unit 51, the correction value sCd from the subtraction unit 52, and the like. For this purpose, the correction value aCd is generated and output as a gradation value to be added to the input image signal Da.

  That is, the switching means 56 selects the initialization value “0” and sets the correction value aCd = 0 when the initialization signal Sif indicates initialization at the interval of the horizontal scanning period, and the gradation change position. The correction value mCd from the calculating means 51 is selected at the pixel position where the gradation value changes with the gradation change position signal Pt = 1 by the signal Pt, and in the gradation flat section where the gradation change position signal Pt = 0. A correction value sCd by the subtracting means 52 (that is, a value obtained by subtracting the gradation change amount dK = Ksl from the correction value pCd of the immediately preceding pixel) is selected and set as the correction value aCd. Further, for the pixels that change continuously with the continuous change determination result sqf = 1, the correction value aCd after the switching is switched to the reset value “0”, and the correction value aCd = 0. The correction value aCd is output to the bit string conversion means 55 and sent to the correction value delay means 54, and is delayed by one pixel and returned to the subtraction means 52 as a delay correction value pCd.

  The correction value delay means 54 delays the correction value aCd from the switching means 53 by one pixel, and outputs a delay correction value pCd that is a correction value for the immediately preceding pixel.

  With the above configuration, the correction value aCd to be added to the input image signal Da is the value (rc) × (Xlm) based on the amplitude limit gradation change amount Xlm and the correction limit coefficient rc, and the inclination data in this order from pixel to pixel. It is obtained as a value that sequentially changes to 0 due to the difference in gradation value by the value Ksl, and when the continuous change determination result sqf = 1, by switching to the correction value aCd = 0, the continuous change with the continuous change determination result sqf = 1 The pixel is a region of pixels that continuously change in the following pixel and the subsequent flat gradation interval, and is generated with the correction value aCd = 0. Therefore, the correction value aCd obtained from the switching means 56 has an accuracy that becomes a fractional value of 1 or less having a change in the gradation value difference of the gradation change amount dK by the inclination data value Ksl in order from the position of the correction value mCd. On the other hand, the correction value aCd is 0 for the pixels in the continuously changing pixel area, and no gradation correction value is added. Even when it is determined that the change in the gradation value is caused by the edge of the image, the correction value mCd = 0 when the correction limit coefficient rc = 0, and the correction value aCd is 0 even in the subsequent pixels. A value is not added, and it can be obtained as a correction value without performing correction for losing the contour information of the image.

  The bit string converting means 55 in the correction bit generating means 50b converts the correction value aCd from the switching means 56 into a bit string value having a predetermined number of bits, and includes an additional bit E indicating a value to be added and a sign bit of the value. The correction bit data Cd is obtained and output from the correction bit generation means 50b to the pixel value calculation means 62.

  In FIG. 17, the configuration of the pixel value calculation means 62 and the delay compensation means 61 in the gradation conversion means 2 is the same as that of the gradation conversion means 1 in FIG. A new output image signal Db is calculated by performing arithmetic processing for subtracting the correction bit data Cd from the correction bit generation means 50b by matching the position of the integer part with respect to the delay-compensated image signal Dd from the means 61. And output.

  In the gradation converting means 2 shown in FIG. 17, the continuous change determining means 70 uses the gradation change amount dfx to determine the region of the pixel where the gradation value monotonously increases or decreases and makes a continuous change, and corrects it. In the bit generation unit 50b, a correction value is obtained from the amplitude limit gradation change amount Xlm, the gradient data value Ksl, and the correction limit coefficient rc. In the pixels in the pixel area, the correction value aCd is 0, and the correction bit data Cd is obtained without adding the gradation correction value. For this reason, according to the gradation converting means 2, it is not necessary to hold an image signal for a flat width when the gradation value changes, and the gradation value changes gently without significantly increasing the circuit scale. When it is determined that the change in the pixel area or the gradation value is caused by the edge of the image, appropriate correction bit data Cd is obtained in the area where the gradation value continuously changes, and the change in the gradation value is appropriately smooth. The 12-bit output image signal Db converted into can be obtained.

  Next, in the image processing apparatus according to the third embodiment, the operation of performing the gradation conversion process of the gradation converting unit 2 will be described. The gradation change amount dfx is calculated based on the difference in gradation value between pixels of the input image signal Da. Based on this gradation change amount, a flat width data predicted value dst predicted from the flat width up to the previous pixel is obtained, and the gradient of the gradation value is obtained from the gradation change amount and the flat width data predicted value. Operations by the pixel value calculation means 62 that obtains the correction bit data Cd and adds the correction bit data to the input image signal Da to output the output image signal Db whose number of gradations has been expanded, The operation of generating the correction bit data Cd in the normal pixel region where the gradation value changes slowly and is not determined by the continuous change determination unit 70 as the pixel region that changes continuously is the gradation conversion unit shown in FIG. 1 It is similar to the flowchart for explaining the operation.

  FIG. 22 is a flowchart showing the operation of the gradation converting means 2. 22, processes that are the same as or correspond to the processes shown in FIG. 12 in the first embodiment are denoted by the same reference numerals. FIG. 22 also shows processing for each pixel in each scanning line.

  In FIG. 22, the input image signal Da is input to the gradation conversion means 2 in step S101 to step S107, step S110, S111 and step S120, the gradation change amount dfx, the flat width data predicted value dst, the correction limiting coefficient rc. FIG. 12 shows the operation until obtaining the gradient data value Ksl indicating the gradient of the gradation value, and obtaining the correction value aCd in steps S112 to S114 and steps S121 and S122 in the correction bit generation means 50b. The same.

The continuous change determination means 70 obtains the gradation change amount dfx at the target pixel position x ₁ and the adjacent pixels x ₁ −1 and x ₁ +1 located before and after the target pixel position x _1, and the magnitude of the obtained gradation change amount dfx and its magnitude From the relationship of the signs, the pixels in the region of the pixels that are continuously changed conforming to the condition 1 and the condition 2 which are the relationships shown in FIGS. 18A and 18B and FIGS. 19A and 19B are determined. Then, the continuous change determination result sqf is generated and output to the correction bit generation means 50b (step S200).

  The correction bit generation means 50b normally obtains the correction value aCd by the operations in steps S112 to S114 and steps S121 and S122, and further receives the continuous change determination result sqf from the continuous change determination means 70 to determine the continuous change. For pixels that change continuously with the result sqf = 1 (step S201), the correction value aCd after switching is switched to the reset value “0” to set the correction value aCd = 0 (step S202). As a result, the correction value aCd can be set to 0 so that the gradation correction value is not added to the pixels in the continuously changing pixel region.

  The obtained correction value aCd is converted into a bit string value having a predetermined number of bits, and is calculated as correction bit data Cd including an additional bit E indicating the value to be added and a sign bit of the value (step S130). ). The correction value aCd is delayed by one pixel and sent to the next pixel process as the correction value pCd for the immediately preceding pixel (step S131).

  From the above operation, the correction value aCd (that is, the correction bit data Cd) to be added to the input image signal Da is the amplitude limit gradation change amount Xlm at the pixel position (Pt = 1) where the gradation value changes. In a gradation flat section (Pt = 0) obtained as a correction value aCd = (rc) × (Xlm) based on the correction limiting coefficient rc, the value at the pixel position where the gradation value changes is sequentially increased. A pixel that is obtained as a value that sequentially changes to 0 due to a difference in gradation value by the inclination data value Ksl, and that changes continuously in a continuous change determination result sqf = 1 and subsequent gradation flat sections. And the correction value aCd = 0 is generated.

  In the pixel value calculation means 62, the correction bit data Cd is aligned with the position of the integer portion of the correction bit data Cd and the image signal Dd (or input image signal Da) compensated for delay so as to match the pixel position of the input image signal Da. By subtracting (or adding), a new output image signal Db is calculated (step S132).

  As described above, in the image processing apparatus according to the third embodiment, in the continuous change determination unit 70, the gradation change amount dfx is used to determine the region of the pixel that continuously increases or decreases in gradation. Then, the correction bit generation means 50b obtains a correction value from the amplitude limit gradation change amount Xlm, the inclination data value Ksl, and the correction limit coefficient rc, and switches the correction value aCd = 0 to a pixel that is continuously changed. The correction value aCd is 0 for the pixels in the continuously changing pixel area, the correction bit data Cd is obtained without adding the gradation correction value, and the pixel value calculation means 62 outputs the correction bit data Cd to the input image signal Da. On the other hand, the correction bit data Cd is subtracted by matching the position of the integer part, thereby converting the gradation value and obtaining the image signal in which the number of bits is expanded. Therefore, according to the image processing apparatus of the third embodiment, the pixel region in which the gradation value continuously changes in the horizontal direction and the case where it is determined that the change in the gradation value is due to the edge of the image. Since it is possible to obtain appropriate correction bit data Cd in a region where the gradation value changes, the processing is performed in real time without holding the image signal for the flat width, and the circuit scale is not significantly increased. Therefore, even when the gradation value changes slowly, when it is determined that the change in the gradation value is caused by the edge of the image, or in a region where the gradation value changes continuously, the change in the gradation value is detected appropriately. Thus, it is possible to obtain a high-quality image signal by obtaining the correct correction bit data Cd, extending the number of gradations of the image signal, and smoothly changing the gradation value with reduced quantization noise or pseudo contour.

  In the image processing apparatus according to the third embodiment, the gradation converting unit 2 obtains the difference between the gradation values +1 and −1 between the pixels, and the gradation change detecting unit 10 determines the level between the adjacent pixels in the horizontal direction. The case where the gradation change amount dfx due to the difference of the tone values is limited to a predetermined range, that is, the range from −1 to +1 has been described. However, as described in the second embodiment, for example, the pixel In the range set by the maximum value (positive value) and the minimum value (negative value), such as when the change in the range from the maximum value +2 to the minimum value -2 is determined, Even when configured to detect a change in value, the continuous change determination means 70 can be applied, and the same configuration can be achieved with the same effects.

  Also in the image processing apparatus according to the third embodiment, the number of gradations m of the input image signal Da is not limited to 8 bits, and may be, for example, a 10-bit image signal. The same effect can be obtained if the value is calculated so that the position of the integer part of the additional bit E in the correction bit data Cd matches the position of the integer part of the image signal Dd.

  In the image processing apparatus according to the third embodiment, the gradation change amount in the horizontal direction is detected to generate correction bit data Cd for the gradation value, and gradation conversion is performed by adding the correction bit data to the image signal. In the above description, the quantization noise is reduced. However, the amount of change in the vertical direction of the input image signal Da is detected, and pixels that change continuously in the vertical direction from the amount of change in the vertical direction are determined. By generating the correction bit data Cd, the change in the gradation value in the vertical direction may be smooth.

  In the third embodiment, points other than the above are the same as in the first or second embodiment.

<< 4 >> Embodiment 4
The image processing apparatuses according to the first to third embodiments detect a change in gradation value in either the horizontal direction or the vertical direction (constant direction) of the image signal, and obtain the gradient of the gradation value. Thus, a gradation conversion process for expanding the number of bits of the input image signal is performed, and an output image signal Db having a higher gradation than the input image signal Da is output. The image processing apparatus according to the fourth embodiment is configured in such a manner that the change in the gradation value in each of the horizontal direction and the vertical direction is detected and the change in the gradation value in the two-dimensional direction is smoothed. This is different from the image processing apparatuses 1 to 3.

  FIG. 23 is a block diagram schematically showing an example of the configuration of an image processing apparatus according to the fourth embodiment of the present invention (that is, an apparatus capable of performing the image processing method according to the fourth embodiment). By detecting the change in the gradation value in each of the horizontal and vertical directions of the image signal and obtaining the gradient of the gradation value, the number of bits of the input image signal is expanded, and the change in the gradation value in the two-dimensional direction is detected. A smooth gradation conversion process is performed.

  In FIG. 23, the image processing apparatus according to the fourth embodiment detects a change in gradation value in the horizontal direction and the vertical direction with respect to an m-bit digital input image signal Da, and responds to the gradient of the gradation value. Gradation conversion processing for expanding the number of bits by adding the obtained value and outputting it as an n-bit output image signal Dc. The horizontal / vertical timing signal generation means 101 and the change of the gradation value in the two-dimensional direction are Gradation conversion means 3 for performing gradation conversion processing for smoothing. The gradation converting unit 3 detects a change in the gradation value in the horizontal direction, and adds a correction value corresponding to the gradient of the gradation value to extend the number of bits, and Vertical direction gradation conversion means 111 is provided that detects a change in gradation value in the vertical direction and performs gradation conversion processing using a correction value corresponding to the gradient of the gradation value.

  Here, the gradation converting means 3 determines the difference of one gradation value (+1 and −1) from the difference of gradation values between adjacent pixels in the horizontal direction and the vertical direction of the input image signal Da. ), A gradation conversion process for expanding the number of gradations by detecting the amount of gradation change is described, and an 8-bit input image signal Da is expanded to a 12-bit output image signal Dc and output. To do.

  The horizontal / vertical timing signal generation means 101 receives the synchronization signal SY for the input image signal Da, and generates a timing signal based on the synchronization signal SY. Since the gradation converting means 3 performs image processing in the two-dimensional direction of the input image signal Da in the horizontal direction and the vertical direction, an initial stage for initializing each process in the gradation converting means 3 for each horizontal synchronizing signal. An initialization signal Sif and a vertical initialization signal vSif for initialization for each vertical synchronization signal are generated. The initialization signal Sif is generated in the same manner as the timing signal generation unit 100, and can be generated as a pulse signal indicating the start timing of the horizontal scanning period. In addition, since the vertical initialization signal vSif is initialized for each vertical synchronization signal, for example, the vertical synchronization signal is used as a reference for the start timing of the vertical scanning period, that is, for one line indicating the start line of the frame. It may be generated as a signal indicating this pixel.

  The gradation conversion means 3 receives the input image signal Da, the initialization signal Sif and the vertical initialization signal vSif from the horizontal / vertical timing signal generation means 101. The gradation converting means 3 detects a change in gradation value in each of the horizontal direction and the vertical direction with respect to the 8-bit input image signal Da, and obtains the gradient of the gradation value, for example, for 4 bits. Correction bit data that is the value of the correction value is obtained, arithmetic processing is performed on the gradation value of the image signal, and gradation conversion is performed by extending the number of bits by adding bits to produce a 12-bit output image Output as signal Dc.

  First, the input image signal Da input to the gradation conversion unit 3 is input to the horizontal direction gradation conversion unit 110 in the gradation conversion unit 3. An input image signal Da and an initialization signal Sif from the horizontal / vertical timing signal generation unit 101 are input to the horizontal direction gradation conversion unit 110. The horizontal gradation conversion means 110 is configured in the same manner as the gradation conversion means 1 (FIG. 1) or the gradation conversion means 2 (FIG. 17) described above, and detects a change in the gradation value in the horizontal direction. The number of bits is extended by adding a value corresponding to the slope of the value, and the result is output as a 12-bit image signal Db. For this reason, the horizontal gradation conversion means 110 is the same as the gradation conversion means in any one of the first to third embodiments.

  The vertical direction gradation conversion means 111 in the gradation conversion means 3 includes a 12-bit image signal Db output from the horizontal direction gradation conversion means 110 and a vertical initialization signal vSif from the horizontal / vertical timing signal generation means 101. Are entered. The vertical direction gradation converting unit 111 removes the lower 4 bits corresponding to the decimal part of the input image signal Da from the 12-bit image signal Db output from the horizontal direction gradation converting unit 110, and the level in the vertical direction. A change in tone value is detected, a correction value corresponding to the gradient of the gradation value is obtained, gradation conversion is performed by adding correction bit data equivalent to that in the horizontal gradation conversion means 110, and a 12-bit output is obtained. Output as an image signal Dc. As a result, a gradation value change is detected not only in the horizontal direction but also in a section where the gradation value changes gently in the vertical direction, and the gradation value change is smooth and a high-quality 12-bit output image. Output as signal Dc.

  FIG. 24 is a block diagram schematically showing an example of the configuration of the vertical direction gradation converting unit 111. A gradation conversion process for detecting a change in gradation value in the vertical direction of the image signal, obtaining a gradient of the gradation value, and extending the number of bits of the image signal is performed. Similar to the conversion means 2, a region of pixels that are continuously changed in the vertical direction is determined, and in this case, the number of gradations is not expanded. Further, when detecting a change in gradation value in the vertical direction and obtaining a gradient of the gradation value, in order to detect a change in one gradation value of the input image signal Da, an input horizontal direction gradation conversion is performed. Of the 12-bit image signal Db from the means 110, the value indicated by the upper 8 bits excluding the lower 4 bits corresponding to the decimal part is used.

  In FIG. 24, the vertical direction gradation converting means 111 comprises 1 line memories (1 line delay means) 81 and 82 for delaying the image signal by one line, and a 12-bit image from the horizontal direction gradation converting means 110. A vertical gradation change that detects a gradation change amount in the vertical direction based on a difference in gradation value between the line delay means 80 that delays the signal Db in units of lines and an adjacent pixel that is positioned vertically above and below the image signal Db. A detecting unit 90, a flat width predicting unit 200 for obtaining a flat width data predicting value obtained by predicting a flat width in the vertical direction, a correction limiting coefficient setting unit 230, a flat width data predicting value from the flat width predicting unit 200, and a vertical An inclination detecting means 240 for detecting the inclination of the gradation value in the vertical direction of the image signal Db from the amount of gradation change from the direction gradation change detecting means 90, and the inputted gradation Correction bit generation means 250 for generating correction bit data as a value to be added to the gradation value of the pixel signal Db, and the phase of the image signal Db delayed by a predetermined time until the correction bit data is generated. A delay compensation unit 210 for matching the pixel values, a pixel value calculation unit 211 for adding the correction bit data from the correction bit generation unit 250 to the image signal Db, and a region of continuously changing pixels in which the gradation value continuously changes in the vertical direction. And a continuous change judging means 270 for judging the above.

  Further, the vertical direction gradation change detecting means 90 in the vertical direction gradation converting means 111 calculates the vertical gradation change amount by calculating the difference between the pixels on the line vertically above and below as the gradation change amount dfxv. Means 91, gradation change amount limiting means 92 for limiting the value of gradation change amount dfxv to be within a predetermined gradation value range, and the value of gradation change amount dfxv is not 0, but its absolute value Is provided with gradation change position detecting means 93 for obtaining a signal indicating the position of a pixel having a change in gradation value with a value greater than 0, and the flat width predicting means 200 in the vertical direction gradation conversion means 111 includes: Flat width (number of pixels) of a gradation flat section in which there is no change in gradation value from a value based on the gradation change amount by the vertical gradation change detection means 90 to a pixel on the immediately preceding line located above the vertical direction. The period when the gradation value is flat A flat width count unit 201 that counts the number of pixels, and a cyclic filter process is performed on the number of pixels of the flat width by the flat width count unit 201 to predict the vertical flat width after the pixel position where the gradation value changes. And a cyclic filter processing means 202 for obtaining a flat width data predicted value that becomes the calculated value.

  In FIGS. 2A to 2C and FIGS. 3A to 3C described in the first embodiment, the horizontal axis indicates the horizontal pixel position x in the horizontal direction. In the case of the direction, the pixels on the line aligned in the screen display line direction (line direction from the top to the bottom of the screen) at the pixel position x in the horizontal direction are shown in FIGS. 2A to 2C and FIGS. This corresponds to the position x of the horizontal pixel, which is the horizontal axis of (c). As shown in FIGS. 2 (a) and 3 (a), the gradual change in gradation value of the level difference of one gradation in the vertical direction of the input image signal Da is shown in FIGS. 2 (c) and 3 (c). As shown in (2), gradation conversion is performed so as to change more smoothly.

  In FIG. 24, the line delay means 80 receives the 12-bit image signal Db from the horizontal gradation conversion means 110, delays the image signal Db in units of lines, and inputs the input image signal Db and its line. Obtain and output a delayed signal. This line delay means 80 can obtain a difference in gradation value between adjacent pixels positioned vertically above and below, and obtain a change from the pixel below one line to obtain a region of continuously changing pixels in the vertical direction. 1 line memories 81 and 82, so that three lines of image signals are obtained. The 1-line memory 81 in the line delay means 80 delays the 12-bit image signal Db from the horizontal direction gradation conversion means 110 by one line to obtain a 1-line delay signal Db1, and the 1-line memory 82 The one-line delay signal Db1 from the line memory 81 is delayed by one line to obtain a two-line delay signal Db2.

FIG. 25 shows the relationship between the pixel positions in the horizontal and vertical directions of the image signal output by the line delay means 80. In FIG. 25, the horizontal direction from left to right is the pixel position in the horizontal direction, and the vertical direction from top to bottom indicates the order of the scanning lines in the vertical direction. In FIG. 25, x represents a pixel position in the horizontal direction, and y represents a pixel position (line number) in the vertical direction. The image signal for 3 lines from the line delay means 80 is a 2-line delay signal Db2 (in FIG. 25, at y ₂ −1) in the horizontal pixel position x _{2 with} respect to the vertical direction from the top to the bottom of the screen. Db2 represents a _{(x 2))} is a one-line delayed signal Db1 to _{y 2} (in FIG. 25, _Db1 (x _2)), in the image signal Db (FIG. 25 which is input to the _y 2 +1 is, Db (x ₂ )) are arranged in order, and the target pixel to be processed is the one-line delay signal Db1, and the scanning line (center line) at which the pixel is located is on the scanning line at the vertical pixel position y delayed by one line.

The two-line delay signal Db2, which is the image signal for three lines obtained by the line delay means 80, the one-line delay signal Db1, and the input image signal Db are output to the vertical gradation change detecting means 90, and the one-line delay signal Db1 is a pixel on the line _{y 2,} is outputted to the delay compensation means 210. Here, in order to detect a change in one gradation value with respect to the input image signal Da to the gradation conversion means 3 in FIG. 23, a decimal number of the 12-bit image signal Db from the horizontal direction gradation conversion means 110 is used. Since the value indicated by the upper 8 bits excluding the lower 4 bits corresponding to the portion may be used, each of the image signals for 3 lines output from the line delay means 80 is sent to the vertical direction gradation change detecting means 90. The value for the upper 8 bits at the input may be input. Therefore, the 2-line delay signal MDb2, the 1-line delay signal MDb1 and the image signal MDb0 having the higher 8 bits are sent to the vertical direction gradation change detecting means 90. The 1-line memory 82 is for obtaining the 2-line delay signal Db2, and since the 2-line delay signal Db2 is only output to the vertical direction gradation change detecting means 90, the 1-line memory 82 is a 1-line memory. The value 8b of the upper 8 bits of the 1-line delay signal Db1 from 81 may be delayed by 1 line. In this case, the size of the line memory can be reduced.

  The vertical direction gradation change detecting means 90 includes a 2-line delay signal MDb2 and a 1-line delay signal MDb1 which are values of upper 8 bits of the image signals for 3 lines obtained by the line delay means 80, and an image signal MDb0. Is calculated from these signals, and the difference in gradation value between pixels adjacent in the vertical direction in the input image signal Da is calculated, and the gradation change amount dfxv in the vertical direction and the pixel position where the gradation value changes. Is detected. That is, in order to detect a change in one gradation value with respect to the input image signal Da, the upper 8 bits excluding the bit corresponding to the decimal part of the 12-bit image signal Db from the horizontal direction gradation converting means 110 are shown. By using the 2-line delay signal MDb2, the 1-line delay signal MDb1, and the image signal MDb0 as values to be processed, the same processing as that of the gradation change detection unit 10 is performed, and the difference in gradation value between pixels adjacent in the vertical direction Is calculated and obtained as the gradation change amount dfxv, and the gradation change amount dfxv is output. A gradation change position signal vPt indicating the pixel position where the gradation value has changed, which is the result of detecting whether the gradation value has changed from the value of dfxv, is output. In the vertical direction gradation change detecting means 90, the gradation change amount dfxv that is the difference from the pixels on one line is used in order to determine the area of the pixels that are continuously changed in the vertical direction in the continuous change determining means 270 described later. As well as the difference from the pixel one line below, and the tone change amount dfxv2.

  The vertical direction gradation change detecting means 90 is composed of a vertical gradation change amount calculating means 91, a gradation change amount limiting means 92, and a gradation change position detecting means 93. Hereinafter, the configuration in the vertical direction gradation change detecting means 90 will be described.

  The vertical gradation change amount calculation means 91 in the vertical direction gradation change detection means 90 receives the 2-line delay signal MDb2, the 1-line delay signal MDb1, and the image signal MDb0 obtained by the line delay means 80, and is vertically A difference in gradation value between pixels adjacent in the direction is calculated and obtained as a gradation change amount in the vertical direction. Here, the vertical gradation change amount calculation unit 91 determines the gradation change amount dfxv between the pixel of interest and the pixel located on the upper line in the vertical direction, and the gradation change amount between the pixel located on the lower line in the vertical direction and the pixel of interest. dfxv2 is obtained.

Now, since the center line of the target pixel to be processed is located is a one-line delay signal MDB1, when the vertical pixel position y _2, in the vertical gradation change amount calculation unit 91, one-line delay signal in the vertical direction y The vertical gradation change amount dfxv is obtained by calculating a value obtained by subtracting the gradation value of the two-line delay signal MDb2 which is the immediately preceding line y ₂ −1 located in the upper line in the vertical direction from MDb1. Further, the gradation change amount dfxv2 is obtained by calculating a value obtained by subtracting the gradation value of the one-line delay signal MDb1 in the vertical direction y from the y ₂ +1 image signal MDb0 located in the vertical lower line. Since the gradation change amount dfxv and the gradation change amount dfxv2 obtained by the vertical gradation change amount calculation means 91 are the difference in the gradation value between the pixels, when the difference in the gradation value between the pixels is 0, In the case of a pixel in a flat gradation section where there is no change in the gradation value, and the pixel in which the gradation value has changed, the direction in which the absolute value of the difference is the difference in the gradation value and the change in the gradation value is increased or decreased Is obtained as a sign of the value (a positive sign “+” when the gradation is increased, and a negative sign “−” when the gradation is decreased).

  The vertical gradation change amount calculation means 91 for obtaining the gradation change amount dfx and the gradation change amount dfxv2 is the above-described gradation change amount calculation means 11 (which calculates the gradation change length for pixels adjacent in the horizontal direction). The means having the same configuration as that described above may be used as means for calculating the amount of gradation change for pixels adjacent in the vertical direction.

  The gradation change amount dfx obtained by the vertical gradation change amount calculation means 91 is output to the correction restriction coefficient setting means 230, and the gradation change amount restriction means 92 in the vertical direction gradation change detection means 90, the floor. The tone change position detecting means 93 is sent, and the tone change amount dfx and the tone change amount dfxv2 between the pixels located on the lower line in the vertical direction are sent to the continuous change determining means 270.

  The gradation change amount limiting unit 92 receives the gradation change amount dfxv from the vertical gradation change amount calculating unit 91, and the gradation change amount dfxv is within a predetermined gradation value range, that is, from −1 to +1. The value is limited so as to fall within the range, and the gradation change amount with the limited value is output as the amplitude limited gradation change amount vXlm. The limits -1 and +1 here are for the gradation converting means 3 to detect the difference of the least significant 1 bit of the 8-bit input image signal Da and the change of 1 gradation value. The amplitude limit gradation change amount vXlm output from the amount limiting unit 92 is composed of three values of −1, 0, and +1.

  The gradation change amount dfxv from the vertical gradation change amount calculation means 91 is also input to the gradation change position detection means 93, and the gradation value changes in the vertical direction from the value of the gradation change amount dfxv. The pixel position is detected, and as a result, a gradation change position signal vPt indicating the pixel position where the gradation value changes according to the binarized value is output.

  The configurations of the tone change amount limiting unit 92 and the tone change position detecting unit 93 are the tone change amounts shown in FIG. 1 except that the change direction obtained by the tone change amount dfxv is a vertical direction. The same configuration as the limiting unit 12 and the gradation change position detecting unit 13 can be adopted.

  Next, in FIG. 24, the flat width predicting means 200 in the vertical direction gradation converting means 111 is based on the gradation change position signal vPt from the vertical direction gradation change detecting means 90, and the pixel immediately before the gradation change position. Cyclic filter processing is performed on the flat width of the gradation flat section in the vertical direction until the flat width data predicted value vdst predicting the flat width of the gradation flat section after the pixel position where the gradation value changes, The inclination detecting means 240 is an inclination indicating the inclination of the gradation value in the vertical direction based on the amplitude limited gradation change amount vXlm from the vertical direction gradation change detecting means 90 and the flat width data predicted value vdst from the flat width predicting means 200. A data value vKsl is obtained. The correction limit coefficient setting unit 230 corrects the correction value as a value that can limit the correction value so that the gradation correction value is not added to the edge of the image, based on the gradation change amount dfxv from the vertical direction gradation change detection unit 90. Set the limiting coefficient vrc. The above configuration is configured to perform the same processing as that of the first embodiment shown in FIG. 1, and the delay processing for one pixel used in each processing is set as the delay processing for one line, and the initialization signal Sif May be configured to detect the change in the gradation value in the vertical direction with the vertical initialization signal vSif.

The continuous change determination means 270 receives the gradation change amount dfxv and the gradation change amount dfxv2 from the vertical direction gradation change detection means 90. The continuous change determination unit 270 performs a line delay of the gradation change amount dfxv, for example, in the vertical pixel position y ₂ of the target pixel and the adjacent pixels y ₂ −1 and y ₂ +1 positioned before and after (upper and lower lines). Obtaining the gradation change amount dfxv, and determining the pixel area where the gradation value monotonously increases or decreases and continuously changes in the vertical direction from the relationship between the magnitude of the obtained gradation change amount and its sign, A continuous change determination result vsqf indicating pixels that are continuously changed is generated and output to the correction bit generation means 250. The gradation change amount dfxv2 is the gradation change amount between the pixel located in the vertical lower line and the target pixel, and thus becomes the gradation change amount at y ₂ +1, and the gradation change amount at y ₂ −1 (dfxv0 and Is obtained by delaying the gradation change amount dfxv by one line.

The continuous change determination unit 270 determines the pixel region that is continuously changed in the vertical direction and generates the continuous change determination result vsqf, as in the continuous change determination unit 70 shown in FIG. Is the gradation change amount dfxv0 at y ₂ −1 arranged in the vertical direction, the gradation change amount dfxv at y _{2, and} the gradation change amount dfxv2 at y ₂ +1, and the case where the condition 1 or condition 2 is satisfied may be determined. .

  The correction bit generation unit 250 includes a vertical inclination data value vKsl from the inclination detection unit 240, a vertical initialization signal vSif from the horizontal / vertical timing signal generation unit 101, and a vertical gradation change detection unit 90. The gradation change position signal vPt, the amplitude limit gradation change amount vXlm, the correction restriction coefficient vrc from the correction restriction coefficient setting unit 230, and the continuous change determination result vsqf from the continuous change determination unit 270 are input. Is done. The correction bit generation unit 250 is processed in the same manner as the correction bit generation unit 50b in FIG. 17 of the third embodiment, and the gradient data value vKsl is set as the gradation change amount dKv for each adjacent pixel of the correction value (dKv = vKsl). Initialization is performed for each vertical scanning period (frame) by the vertical initialization signal vSif. Further, the correction bit generation unit 250 determines the vertical gradation based on the gradation change amount dKv (that is, the slope data value vKsl), the amplitude limit gradation change amount vXlm, and the correction limit coefficient vrc in accordance with the gradation change position signal vPt. Correction value vaCd is obtained, and correction bit data vCd is generated using the correction value as a bit string including an additional bit Ev including a decimal part of the gradation value of the input image signal Da and a sign bit of the value to be added. In addition, when the correction bit generation unit 250 obtains the correction value vaCd, the correction of the gradation is performed for the pixels in the pixel region that continuously changes in the vertical direction based on the continuous change determination result vsqf from the continuous change determination unit 270. The correction value vaCd is generated as 0 so that no value is added.

  The correction bit generation means 250 corrects the delay if the delay process for one pixel in the correction bit generation means 50b is set as a delay process for one line and the initialization by the initialization signal Sif is performed for each vertical synchronization signal. A vertical gradation correction value vaCd can be obtained by configuring and processing in the same manner as the bit generation means 50b. Then, the obtained vertical correction value vaCd is converted into a bit string value having a predetermined number of bits, and an additional bit Ev indicating a value to be added and a sign bit of the value are obtained as vertical correction bit data vCd. The correction bit generation unit 250 outputs the pixel value calculation unit 221.

  The delay compensation means 210 in the vertical direction gradation conversion means 111 receives a 1-line delay signal Db1 obtained by delaying the 12-bit image signal Db from the horizontal direction gradation conversion means 110 obtained by the line delay means 80 by one line. The delay compensation of the one-line delay signal Db1 is performed so that the delay until the correction bit data vCd output from the correction bit generation unit 250 is obtained and the pixel position of the one-line delay signal Db1 are matched. The signal Dd1 is output. The image signal Dd1 is a center line signal processed by the vertical direction gradation converting means 111, and is a 12-bit image signal.

  The pixel value calculation unit 211 receives the delay compensated image signal Dd1 from the delay compensation unit 210 and the vertical correction bit data vCd from the correction bit generation unit 250. The pixel value calculation unit 210 performs a calculation process of subtracting or adding the correction bit data vCd from the correction bit generation unit 250 to the delay compensated image signal Dd1 according to the sign by matching the position of the integer part. Then, a new output image signal Dc is calculated and output. Since the correction bit data vCd including a decimal part corresponding to the change in the vertical gradation value is added to the gradation value of the image signal Db1, not only the horizontal direction but also the vertical gradation value changes. An output image signal Dc corrected to be smooth is obtained, and this output image signal Dc becomes the output of the gradation converting means 3.

  The pixel value calculation unit 211 can be configured in the same manner as the pixel value calculation unit 62, and the additional bit Ev indicating the value to be added in the correction bit data vCd is the gradation value of the image signal Dd1 (or image signal Db) that has been delay compensated. On the other hand, since it includes a decimal part corresponding to the change in the gradation value in the vertical direction, the pixel value calculation unit 211 uses the correction bit data vCd by aligning the position of the integer part with the gradation value of the input image signal. The output image signal Dc after the value is subtracted is converted so that the change in the gradation value in the vertical direction as well as the horizontal direction becomes smooth, and the change in the gradation value can be expressed more smoothly.

  FIG. 26 is a diagram showing the relationship between the image signal, the correction bit data, and the output image signal in the gradation converting means 3. FIG. 26 shows the input image signal Da, the correction bit data Cd in the horizontal gradation conversion means 110 and the output horizontal direction processed image signal Db, and the vertical correction bit data vCd in the vertical direction gradation conversion means 111. And the relationship between the output image signal Dc. Here, the input image signal Da is m = 8 bits, the correction bit data Cd is a sign bit and an additional bit E (4 bits), the correction bit data vCd is a sign bit and an additional bit Ev (4 bits), and the horizontal direction processed image The case where the signal Db and the output image signal Dc are n = 12 bits will be described.

  In FIG. 26, the correction bit data Cd and the correction bit data vCd are obtained by detecting a change in gradation value in the horizontal direction and the vertical direction, which is a level difference of one gradation with respect to the input image signal Da, and obtaining an inclination. Therefore, it is obtained as additional bits E and Ev indicating a decimal part with respect to the input image signal Da. Therefore, similarly to the pixel value calculation means 62, the pixel value calculation means 211 in the vertical gradation conversion processing in the vertical direction gradation conversion means 111 also aligns the position of the integer part, and the lower 4 bits of the image signal Dd1. The output image signal Dc is calculated by performing an arithmetic process of subtracting or adding a value obtained by adding the additional bit Ev4 bit of the correction bit data vCd to the position according to the sign. The output image signal Dc has a bit string extending downward with respect to the input image signal Da, and smoothly converts a change in gradation value not only in the horizontal direction but also in the vertical direction with respect to the gradation value of the original input image signal Da. Therefore, the resolution of one gradation of the output image signal Dc is higher than that of the input image signal Da, quantization noise or pseudo contour is further reduced in the two-dimensional direction, and a highly accurate gradation can be expressed. become.

  From the above, in the gradation converting unit 3 according to FIG. 24, the horizontal direction gradation converting unit 110 predicts the flat width in the horizontal direction based on the gradation change amount dfx which is the change in the gradation value in the horizontal direction. The data prediction value dst is obtained, and the gradient data value Ksl in the horizontal direction is obtained to convert the gradation, and the gradation in the vertical direction gradation conversion means 111 is also a gradation that is a change in the gradation value in the vertical direction. Based on the change amount dfxv, a flat width data predicted value vdst and a slope data value vKsl obtained by predicting a flat width in the vertical direction are obtained, and gradation is converted by the correction bit data vCd in the vertical direction based on the slope data value vKsl. Therefore, in the gradation converting means 3 shown in FIG. 24, it is not necessary to hold the image signal for the flat width in the horizontal direction, and it is necessary to hold the image signal for the detected flat width in the vertical direction with a line delay. This means that less memory is required. Therefore, according to the gradation conversion means 3, it is determined that the pixel area in which the gradation value changes gently in the two-dimensional direction and the change in the gradation value are caused by the edge of the image without greatly increasing the circuit scale. Accordingly, 12-bit output image signal Dc in which the change of the gradation value not only in the horizontal direction but also in the vertical direction is more smoothly converted is obtained.

  Next, in the image processing apparatus according to the fourth embodiment, the gradation conversion operation in each of the horizontal direction gradation conversion means 110 and the vertical direction gradation conversion means 111 in the gradation conversion means 3, that is, in the input image signal Da. Based on the gradation change amount obtained from the difference in gradation value between pixels, the predicted flat width data dst and vdst are obtained from the flat width up to the previous pixel, and the gradation change amount and the flat width data prediction are obtained. An image signal whose number of gradations is expanded by obtaining the gradient of the gradation value from the value, generating correction bit data Cd, vCd based on the gradation change amount and gradient, and adding the correction bit data to the input image signal Da 12 and the operation of switching the value of the correction bit data by determining the region of the pixel that continuously changes, or the flowchart for explaining the operation of the gradation converting means 1 shown in FIG. Is similar to the flowchart for explaining the operation of gradation conversion means 2 shown. In these flowcharts, however, the pixel position x for the horizontal direction gradation converting means 110 is the pixel position in the horizontal direction, and the pixel position x for the vertical direction gradation converting means 111 is the pixel position in the vertical direction.

  In the description of the gradation converting means 3 in FIG. 23 described above, the gradation change amount when detecting the change in the gradation value of the input image signal Da is the difference of the least significant 1 bit, that is, between the pixels. Although the gradation value difference +1 and −1 are changed, the present invention is not limited to this mode, and as shown in FIG. 15 of the second embodiment, the horizontal direction gradation in the gradation converting means 3 is used. In each of the conversion unit 110 and the vertical direction gradation conversion unit 111, the value of the gradation change amount dfx is limited based on the predetermined maximum value (positive value) and minimum value (negative value), and the image signal The number of gradations may be extended when the gradation value changes within a difference of gradation values greater than one gradation.

  For example, in the case of obtaining a change in the range from the maximum value +2 to the minimum value −2 of the difference in gradation value between pixels, as shown in FIG. 27A, the correction bit data Cd and vCd are used as sign bits. As the additional bits E and Ev5 bits, the additional bits E and Ev are composed of a 1-bit integer part and a 4-bit decimal part with respect to the input image signal Da, and the position of the integer part in the additional bits E and Ev is input image. A value matched with the position of the integer part of the signal Da may be subtracted or added to the input image signal Da according to the sign. In this case, not only the change of the gradation value of one gradation which is the minimum gradation value of the input image signal Da but also the quantization noise of one gradation or more (for example, due to gradation jump) in the input image signal Da. ), The pixel area in which the gradation value changes gradually in the two-dimensional direction of the horizontal direction and the vertical direction, and the change in the gradation value is Appropriate correction bit data in the case where it is determined to be an edge is obtained, and a 12-bit output image signal Dc in which a change in gradation value is more smoothly converted is obtained.

  Further, the resolution in the horizontal direction is often high in the image signal, and in the gradation converting unit 3 in FIG. 23, the horizontal direction processing is first performed by the horizontal direction gradation converting unit 110 and then the vertical direction processing is performed. Since this is a configuration in which gradation value change (a range to be limited) when detecting a change in gradation value is set to a value that differs between the horizontal direction and the vertical direction, for example, FIG. As shown in FIG. 5, for example, a difference between two gradations (difference between gradation values between pixels +2 and −2) in the horizontal direction, and a difference of one gradation in the vertical direction, In other words, the gradation value difference between pixels +1 and −1 may be changed, and the weight of the difference between gradation values detected in the horizontal direction may be increased in the vertical direction to extend the number of gradations.

  Further, the vertical direction gradation converting means 111 shown in FIG. 24 is configured in the same manner as the gradation converting means 2 in FIG. 17, and includes a continuous change determining means 270 for determining a region of continuously changing pixels in the vertical direction. The delay means 80 is composed of one-line memories 81 and 82 so as to be able to determine a region of continuously changing pixels in the vertical direction by obtaining a change from the pixel below one line, and image signals for three lines. However, the vertical direction gradation converting means 111 may be configured in the same manner as the gradation converting means 1 in FIG. 1 and the continuous change determining means 270 may not be used, and the same effect can be obtained. In this case, since the line delay unit 80 only needs to obtain a one-line delay signal, the line delay unit 80 may be constituted by the one-line memory 81 and obtain an image signal for two lines.

  In addition, the case where the decimal part of the additional bits E and Ev in the correction bit data Cd and vCd is 4 bits has been described, but it may be other than 4 bits, and the number of bits in the decimal part may be increased to increase the number of bits. By expressing the correction bit data Cd, vCd (that is, the correction values aCd, vaCd) with numbers, it is possible to obtain an image signal that can display a more accurate change in the gradation value with higher accuracy.

  As described above, in the image processing apparatus according to the fourth embodiment, the horizontal direction gradation converting unit 110 predicts the horizontal flat width based on the gradation change amount dfx that is the change in the horizontal direction gradation value. The obtained flat width data predicted value dst is obtained, the horizontal inclination data value Ksl is obtained and the gradation is converted, and the vertical direction gradation converting means 111 similarly changes the gradation value in the vertical direction. A flat width data predicted value vdst obtained by predicting a flat width in the vertical direction is obtained from a certain gradation change amount dfxv, and a gradation data is obtained by obtaining a vertical inclination data value vKsl. For this reason, according to the image processing apparatus of the fourth embodiment, it is not necessary to hold an image signal corresponding to a flat width, a large amount of memory is not required, and the circuit scale is not significantly increased. Even if it is determined that the gradation value changes slowly and the gradation value changes due to the edge of the image, the change in the gradation value is detected to obtain appropriate correction bit data, and the horizontal direction In addition to expanding the number of gradations of the image signal so that the change in gradation value in the vertical direction becomes smoother, the change in gradation value with reduced quantization noise or pseudo contour in the two-dimensional direction is smooth, A high-quality image signal can be obtained.

  In the image processing apparatus according to the fourth embodiment, the number of gradations of the input image signal Da is not limited to 8 bits, and may be, for example, a 10-bit image signal. In the vertical direction gradation converting means 111, a value is calculated in which the position of the integer part of the additional bits E and Ev in the correction bit data Cd and vCd matches the position of the integer part of the input image signal Da. If configured, the same effect can be achieved.

  In the fourth embodiment, points other than those described above are the same as those in the first, second, or third embodiment.

<< 5 >> Embodiment 5
In the first to fourth embodiments, the image processing apparatus and the image processing method to which the present invention is applied have been described. However, the present invention can also be applied to an image display apparatus. FIG. 28 is a block diagram schematically showing an example of the configuration of the image display device 5 according to the fifth embodiment of the present invention. As shown in FIG. 28, the image display device 5 of the fifth embodiment includes an image signal input terminal 501, a reception processing unit 502, a gradation conversion unit 500, and a display unit 504. The gradation conversion means 500 is, for example, the gradation conversion means 1 in the image processing apparatus according to the first or second embodiment, or the gradation conversion means 2 in the image processing apparatus according to the third embodiment. It is constituted by the gradation converting means 3 in the image processing apparatus of aspect 4. The gradation conversion unit 500 is configured to extend the number of bits of the input image signal and output the gradation-converted multi-gradation image signal to the display unit 504.

  The input terminal 501 receives a TV broadcast signal, a playback signal such as a DVD or VTR by the playback device, and a signal from the TV broadcast receiving device. A signal input to the input terminal 501 is sent to the reception processing unit 502.

  The reception processing unit 502 performs processing for converting a signal input through the input terminal 501 into a format that can be processed by the gradation conversion unit 500 in the subsequent stage. For example, when an analog signal is input, the reception processing unit 502 performs input signal processing such as processing to convert the analog signal into a digital signal and processing to separate the synchronization signal. For example, when receiving MPEG data, the reception processing unit 502 performs a process of decoding the MPEG data. The reception processing unit 502 outputs the processed image signal to the gradation conversion unit 500.

  The gradation converting means 500 is the gradation converting means 1 in the image processing apparatus according to the first or second embodiment, or the gradation converting means 2 in the image processing apparatus according to the third embodiment, or the fourth embodiment. The same gradation conversion processing as that of the gradation conversion means 3 in the image processing apparatus of FIG.

  The display unit 504 receives the image signal with the number of bits expanded from the gradation conversion unit 500, and displays the image with the displayable number of bits based on the received image signal.

  As described above, according to the image display device 5 of the fifth embodiment, any one of the image processing devices or image processing methods of the first to fourth embodiments is applied to the gradation converting means 500. Therefore, when the number of bits of the input image signal is smaller than the number of bits that can be displayed by the display unit 504, or a display device (for example, a liquid crystal device, a plasma display, etc.) provided in the display unit 504 is a high-luminance device. Even in this case, it is possible to extend the gradation of the image signal to a sufficient number of gradations even in a section where the gradation value changes very slowly by processing in real time without greatly increasing the circuit scale. it can. Therefore, according to the image display device 5 of the fifth embodiment, the quantization noise and the pseudo contour are reduced, the gradation value is smoothly changed, and an image signal with an extended number of gradations is displayed. Can do.

<< 6 >> Embodiment 6
The image display device 5 according to the fifth embodiment includes one gradation conversion unit 500, but the image display device 6 according to the sixth embodiment includes a plurality of gradation conversion units. FIG. 29 is a block diagram schematically showing an example of the configuration of the image display device 6 according to the sixth embodiment of the present invention. 29, the same or corresponding components as those in FIG. 28 are denoted by the same reference numerals. 29, the image display apparatus 6 according to the sixth embodiment is different from the image display apparatus 5 according to the fifth embodiment in that a gradation correction unit 503 and a gradation conversion unit 510 as signal processing units are provided. To do. The gradation correction unit 503 is a unit that performs gradation correction such as expansion of the dynamic range of the image signal and improvement of contrast. The gradation conversion means 510 is the gradation conversion means 1 in the image processing apparatus according to the first or second embodiment, or the gradation conversion means 2 in the image processing apparatus according to the third embodiment, or the fourth embodiment. In this image processing apparatus, gradation conversion processing similar to that performed by the gradation conversion means 3 is performed, and an image signal having a gradation higher than that of the input image signal is output to the display means 504. The gradation conversion unit 510 performs quantization correction such as expansion of the dynamic range of the image signal and improvement of contrast by the gradation correction unit 503, and the quantization noise of the image signal increased with the gradation correction. In order to reduce (gradation jump), gradation conversion processing is performed on the image signal after gradation correction.

  An image signal input from the input terminal 501 is received by the reception processing unit 502, and an image signal in a predetermined format is output to the gradation conversion unit 500. The gradation conversion unit 500 performs gradation conversion processing for expanding the number of bits on the input image signal to reduce quantization noise. The configuration and operation so far are the same as those in the fifth embodiment.

  The gradation correction unit 503 receives an image signal from the gradation conversion unit 500 that is an image signal having a higher gradation than the input image signal. The gradation correction unit 503 performs gradation correction such as expansion of the dynamic range of the input image signal and improvement of contrast. In the gradation correction, a process for converting the gradation of a certain section of the input image signal at a predetermined magnification is performed. As a result, the dynamic range of the displayed image is expanded, and an image having a clear contrast and high contrast is displayed. However, the gradation correction performed by the gradation correcting unit 503 makes it easy for a gradation jump to occur. As a result, the quantization noise increases. That is, for example, when correction is made such that the gradation value is quadrupled, the gradation of the output image has only values every four gradations, and even in an area where the image gradually becomes brighter, The gradation value changes every four gradations, and this gradation jump becomes conspicuous as quantization noise.

  The image signal output from the gradation correction unit 503 is input to the gradation conversion unit 510. The gradation conversion unit 510 performs gradation conversion processing for expanding the number of bits for the input image signal by the same processing as the gradation conversion unit 500, and processes the change in gradation value in the image signal to be smooth. The obtained image signal is output to the display means 504.

  Here, when the gradation correction unit 503 performs a process that generates a gradation jump of 4 gradations, for example, the gradation conversion unit 510 is set to 4 as described in the second embodiment. What is necessary is just to set so that the difference between the gradations, that is, the change in the gradation value in the range from +4 to -4 can be detected. In this way, the change value of the gradation value detected by the gradation converting means 510 may be determined according to the characteristics of the gradation correcting means 503. The configuration and operation of the gradation conversion means 510 in this case are the same as those of any of the gradation conversion means in the first to fourth embodiments.

  The display unit 504 receives an image signal in which the number of bits has been expanded by processing the gradation value change from the gradation conversion unit 510 to be smooth, and the number of bits that can be displayed based on the received image signal To display the image.

  As described above, according to the image display device 6 of the sixth embodiment, after the quantization noise is reduced by the gradation conversion unit 500, the dynamic range expansion and the contrast correction processing are performed by the gradation correction unit 503. Even in this case, the gradation jump is generated by setting the change value (maximum value, minimum value) of the gradation value detected by the gradation conversion means 510 according to the characteristics of the gradation correction means 503. It is possible to perform gradation conversion processing for gradation jump reduction without searching for gradation. Therefore, according to the image display device 6 of the sixth embodiment, the circuit scale is greatly increased even when the display device (for example, a liquid crystal device, a plasma display, etc.) provided in the display unit 504 is a high-luminance device. In real-time processing, the gradation of the image signal can be expanded to a sufficient number of gradations even in a period where gradation values change very slowly, reducing quantization noise and pseudo contours. In addition, an image signal having a smooth gradation value change and an extended number of gradation levels can be displayed.

  FIG. 29 shows the case where the gradation correction unit 503 for performing gradation correction is arranged at the subsequent stage of the gradation conversion unit 500, but in place of the gradation correction unit 503, signal processing other than gradation correction is performed. Even when a means (not shown) for increasing quantization noise due to gradation jump is provided, the gradation conversion means 510 can reduce the quantization noise. In this case, the change value (maximum value, minimum value) of the gradation value detected by the gradation conversion means 510 is increased by image processing if it is determined according to the quantization noise characteristics of the signal processing means. It can be configured to reduce quantization noise.

  1, 2, 3 gradation conversion means, 5, 6 image display device, 10 gradation change detection means, 11 gradation change amount calculation means, 12 gradation change amount restriction means, 13 gradation change position detection means, 20 flat Width prediction means, 21 flat width count means, 22 cyclic filter processing means, 23 pixel count means, 24 delay means, 25 coefficient 1 multiplication means, 26 calculation means, 27 coefficient 2 multiplication means, 28 switching means, 29 filter output delay Means 30 correction limit coefficient setting means 31, 33 absolute value calculation means 32 differential low-frequency component extraction means 34 magnification conversion means 35 maximum value selection means 36 coefficient conversion means 40 inclination detection means 41 inclination calculation means 42 switching means, 43 slope delay means, 50, 50b correction bit generating means, 51 computing means 52 subtraction means, 53, 56 switching means, 54 correction value delay means, 55 bit string conversion means, 61 delay compensation means, 62 pixel value calculation means, 70 continuous change determination means, 71, 72 condition 1 determination means, 73 condition 1 composition Means, 74 condition 2 determination means, 75 composition means, 80 line delay means, 81, 82 1 line memory, 90 vertical gradation change detection means, 91 vertical gradation change calculation means, 92 gradation change restriction means, 93 gradation change position detection means, 110 horizontal direction gradation conversion means, 111 vertical direction gradation conversion means, 200 flat width prediction means, 201 flat width count means, 202 cyclic filter processing means, 211 vertical pixel value calculation means, 230 correction limit coefficient setting means, 240 inclination detection means, 250 correction bits Generation means, 270 continuous change determination means, 500,510 gradation conversion means, 501 input terminal, 502 reception processing means, 504 display means, 503 gradation correction means, aCd correction value, Cd correction bit data, Cnt flat width count value Da input image signal (input pixel data), Db output image signal (output pixel data), Dc output image signal (output pixel data), dfx gradation change amount, dst flat width data predicted value, E additional bit data, Ev Vertical additional bit data, Ksl slope data value, La (x) input image signal tone value, Lb (x) output image signal tone value, Pt tone change position signal, rc correction limit coefficient, Sif initialization Signal, sqf continuous change determination result, vCd correction bit data, vdst flat width Data prediction value, vKsl slope data value, vPt gradation change position signal, vrc correction limit coefficient, vSif initialization signal, vsqf continuous change determination result, vXlm amplitude limit gradation change amount, x horizontal pixel position, Xlm amplitude limit Tone change amount.

Claims (19)

An input image signal composed of discrete data in the time direction and the spatial direction is inputted, and composed of post-conversion data generated by a conversion process that expands the number of gradations of the input image signal and corrects the gradation value. An image processing apparatus having a function of outputting an output image signal,
Gradation change information including a gradation change amount that is a difference between gradation values of pixels arranged adjacent to each other from the input image signal, and a gradation change position that is a pixel position where the value of the gradation change amount is not 0 Gradation change detecting means for detecting
Each time a pixel at the gradation change position is detected from the gradation change information, the pixel at the detected gradation change position is used as a reference pixel, and the flat width of the gradation flat section immediately after the reference pixel is set. A means for generating a predicted flat width data value that is a predicted value, the pixel having the same gradation value immediately before the reference pixel and the immediately preceding flat width of the continuous gradation flat section and immediately before the reference pixel is detected. A flat width predicting means for generating a flat width data predicted value for predicting a flat width of a gray level flat section immediately after the reference pixel based on the previous flat width data predicted value generated in the reference pixel;
An inclination for obtaining an inclination data value used for setting an inclination of the gradation value of the converted data in the gradation flat section immediately after the reference pixel, based on the gradation change information and the flat width data predicted value. Detection means;
It is determined whether the gradation change at the gradation change position is a gradation change due to an edge of the image based on the gradation change amount, and the gradient of the gradation value of the output image signal is determined according to the determination result. Correction limit coefficient setting means for setting a correction limit coefficient for limiting
Correction bit generation means for determining a correction value of a gradation value of the input image signal using the gradation change information, the inclination data value, and the correction limiting coefficient, and generating correction bit data corresponding to the correction value When,
Image value processing means comprising: pixel value calculation means for subtracting or adding a value corresponding to the correction bit data from the gradation value to generate the output image signal composed of the converted data. apparatus. From the gradation change amount, it is determined whether or not the gradation value change is a continuous change region that occurs for each of a plurality of adjacent pixels or for each of a plurality of adjacent pixels across a predetermined number of pixels. It further comprises a continuous change determination means for outputting a continuous change determination result,
The image processing apparatus according to claim 1, wherein the correction bit generation unit switches a value adopted as the correction value in accordance with the continuous change determination result. The correction bit generation means obtains the correction value including a value corresponding to a decimal part of the gradation value of the input image signal, generates the correction bit data from a value obtained by quantizing the correction value,
The pixel value calculation means includes a decimal part for the input image signal by subtracting or adding the correction bit data from the gradation value of the input image signal, and has a larger number of gradations than the input image signal. The image processing apparatus according to claim 1, wherein the output image signal is generated. The gradation change detecting means is
A gradation change amount calculating means for calculating a difference in gradation value between adjacent pixels in either the horizontal direction or the vertical direction of the image from the input image signal, and outputting the difference as the gradation change amount;
A gradation change amount limiting unit that limits a range of values of the gradation change amount and generates an amplitude-limited gradation change amount that limits the value of the gradation change amount;
Gradation change position detecting means for generating the gradation change position signal from the magnitude of the value of the gradation change amount,
The gradation change amount, the amplitude-limited gradation change amount, and the gradation change position signal are output as the gradation change information. Image processing device.   The gradation change amount limiting means limits the value of the gradation change amount within a range from a maximum value that is a predetermined positive value to a minimum value that is a predetermined negative value, The image processing apparatus according to claim 4, wherein the image processing apparatus outputs the amplitude-limited gradation change amount.   The maximum value and the minimum value are a value that is a minimum difference in gradation value changes in the input image signal, or a value that is an integral multiple of a value that is the minimum difference. 5. The image processing apparatus according to 5. The flat width predicting means is:
Flat width count means for outputting a count value of the number of pixels in the gradation flat section as a flat width count value indicating the flat width;
For each of the reference pixels, the flat width count value of the flat width obtained up to the pixel immediately before the reference pixel by performing a cyclic filter process on the filter processing output up to the pixel immediately before the reference pixel. 7. A cyclic filter processing unit that obtains a low-frequency component of the value and outputs the obtained value as the flat width data prediction value. 8. Image processing apparatus. The inclination detecting means is
The gradient used when setting the gradient of the gradation value of the converted data based on the amplitude-limited gradation variation amount in which the gradation variation value is limited to a predetermined range and the flat width data predicted value. A slope calculating means for obtaining
For each reference pixel, the gradient of the gradation value obtained by the gradient calculation means is selected as the gradient data value, and the gradient value of the previous pixel is used as the gradient data value for pixels other than the reference pixel. Switching means to select,
8. The output from the switching means is output as the inclination data value indicating the inclination of the gradation value of the image signal in the interval corresponding to the gradation flat interval. The image processing apparatus according to item 1. The correction limit coefficient setting means is
If the absolute value of the gradation change amount is larger than a predetermined threshold value, it is determined that the gradation change amount value is due to an edge of the image, the correction limit coefficient value is set to 0,
When the absolute value of the gradation change amount is equal to or less than the threshold value, the value of the correction limiting coefficient is set to a value within 1 and less than 0 according to the absolute value of the gradation change amount. The image processing apparatus according to any one of claims 1 to 8, wherein the image processing apparatus includes: The correction limit coefficient setting means is
Absolute value calculating means for obtaining an absolute value of the gradation change amount;
A low frequency component extracting means for extracting a low frequency component of the gradation change amount and outputting it as a differential low frequency component;
Absolute value calculating means for obtaining an absolute value of the differential low-frequency component;
A magnification conversion means for performing a magnification conversion by multiplying the absolute value of the difference low-frequency component by a preset value, and outputting the magnification-converted differential low-frequency component after the magnification conversion;
A maximum value selecting means for obtaining an absolute value of the gradation change amount and a maximum value of the magnification conversion difference low-frequency component, and outputting the absolute value as a maximum difference absolute value;
The image processing apparatus according to claim 9, further comprising: coefficient conversion means for generating the correction limiting coefficient from the value of the maximum difference absolute value. The correction bit generation means includes
An arithmetic means for obtaining a correction value for the gradation value of the input image signal from the amplitude-limited gradation change amount and the correction restriction coefficient in which the value of the gradation change amount is limited to a predetermined range;
Subtraction means for obtaining the inclination data value as a value of change for each pixel of the correction value, subtracting the inclination data value from the correction value in the immediately preceding pixel, and outputting the subtraction result;
Based on the value of the gradation change amount, the correction value obtained by the calculation means is selected for pixels whose gradation value changes, and the subtraction by the subtraction means is performed for pixels other than the pixels whose gradation value changes. Switching means for selecting a result and outputting the selected result as a correction value for the gradation value of the input image signal;
From the correction value of the pixel whose gradation value changes, a correction value that sequentially changes for each pixel by the inclination data value is obtained, and a quantization value corresponding to a decimal part is obtained with respect to the gradation value in the input image signal. 11. The image processing apparatus according to claim 1, further comprising: a bit string conversion unit that generates correction bit data having the bit string conversion unit.   The continuous change determination means determines whether or not the continuous change region is based on the gradation change value and the sign of the gradation change amount in the reference pixel and pixels adjacent to the reference pixel. The image processing apparatus according to claim 2, wherein a signal indicating that the pixel is included in the continuous change region is output as the continuous change determination result. An input image signal composed of discrete data in the time direction and the spatial direction is inputted, and composed of post-conversion data generated by a conversion process that expands the number of gradations of the input image signal and corrects the gradation value. An image processing method for outputting an output image signal,
Gradation change information including a gradation change amount that is a difference between gradation values of pixels arranged adjacent to each other from the input image signal, and a gradation change position that is a pixel position where the value of the gradation change amount is not 0 A gradation change detecting step for detecting
Each time a pixel at the gradation change position is detected from the gradation change information, the pixel at the detected gradation change position is used as a reference pixel, and the flat width of the gradation flat section immediately after the reference pixel is set. A step of generating a flat width data predicted value, which is a predicted value, immediately before a pixel having the same gradation value immediately before the reference pixel is detected immediately before the flat width of a continuous gradation flat section and the reference pixel; A flat width prediction step for generating a flat width data prediction value by predicting a flat width of a gray level flat section immediately after the reference pixel based on the previous flat width data prediction value generated in the reference pixel;
An inclination for obtaining an inclination data value used for setting an inclination of the gradation value of the converted data in the gradation flat section immediately after the reference pixel, based on the gradation change information and the flat width data predicted value. A detection step;
It is determined whether the gradation change at the gradation change position is a gradation change due to an edge of the image based on the gradation change amount, and the gradient of the gradation value of the output image signal is determined according to the determination result. A correction limiting coefficient setting step for setting a correction limiting coefficient for limiting
A correction bit generation step of obtaining a correction value of a gradation value of the input image signal using the gradation change information, the inclination data value, and the correction restriction coefficient, and generating correction bit data corresponding to the correction value When,
A pixel value calculating step of subtracting or adding a value corresponding to the correction bit data from the gradation value to generate the output image signal composed of the converted data. Method. Based on the amount of gradation change described above, it is determined whether or not the gradation value change is a continuous change region that occurs for every adjacent pixel or every adjacent pixel across a predetermined number of pixels, and a continuous change determination result is output. Further comprising a continuous change determining step,
The image processing method according to claim 13, wherein, in the correction bit generation step, a value adopted as the correction value is switched according to the continuous change determination result. The flat width prediction step includes
A flat width count step for outputting a count value of the number of pixels in the gradation flat section as a flat width count value indicating the flat width;
For each of the reference pixels, the flat width count value of the flat width obtained up to the pixel immediately before the reference pixel by performing a cyclic filter process on the filter processing output up to the pixel immediately before the reference pixel. The image processing method according to claim 13, further comprising: a cyclic filter processing step of obtaining a low frequency component of the value and outputting the obtained value as the flat width data predicted value. The inclination detection step includes
The gradient used when setting the gradient of the gradation value of the converted data based on the amplitude-limited gradation variation amount in which the gradation variation value is limited to a predetermined range and the flat width data predicted value. A slope calculating step for obtaining
For each of the reference pixels, the gradient of the gradation value obtained by the gradient calculation step is selected as the gradient data value, and the gradient of the gradation value in the immediately preceding pixel is selected as the gradient data value for pixels other than the reference pixel. A switching step to select, and
16. The data value selected in the switching step is output as the inclination data value indicating the inclination of the gradation value of the image signal in an interval corresponding to the gradation flat interval. The image processing method according to any one of the above. The correction limit coefficient setting step includes
If the absolute value of the gradation change amount is larger than a predetermined threshold value, it is determined that the gradation change amount value is due to an edge of the image, the correction limit coefficient value is set to 0,
When the absolute value of the gradation change amount is equal to or less than the threshold value, the value of the correction limiting coefficient is set to a value within 1 and less than 0 according to the absolute value of the gradation change amount. The image processing method according to any one of claims 13 to 16, wherein: The image processing apparatus according to any one of claims 1 to 12,
An image display device comprising: display means for displaying an image based on the output image signal in which the number of gradations output from the image processing device is expanded. A first image processing means having the same configuration as the image processing apparatus according to any one of claims 1 to 12,
Signal processing means for processing a signal output from the first image processing means;
A second image processing unit having the same configuration as the image processing apparatus according to any one of claims 1 to 12, which performs gradation conversion processing on a signal output from the signal processing unit,
An image display apparatus comprising: display means for displaying an image based on an image signal with an expanded number of gradations output from the second image processing means.

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