JP2017156721A - Image processing device and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve both suppression of image quality deterioration in a low gradation part when executing linear processing and suppression of an increase in circuit scale.SOLUTION: An image processing device comprises: conversion means for converting a first gradation range, a second gradation range and a third gradation range of an image signal corrected with regard to response characteristics of a display according to first conversion characteristics, second conversion characteristics and third conversion characteristics respectively; and processing means for processing a conversion signal obtained as a result of conversion by the conversion means. The first gradation range is lower than the third gradation range in gradation, and the second gradation range is between the first gradation range and the third gradation range. The third conversion characteristics correspond to the response characteristics, the first conversion characteristics are linear, and the second conversion characteristics are determined so as to smoothly join the first conversion characteristics and the third conversion characteristics in the second gradation range.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image processing apparatus and an image processing method.

  In recent years, image display apparatuses including various display devices such as a liquid crystal display device such as a TV receiver and a PC monitor have been put into practical use. The image display device performs various image processing on the input image signal, and then outputs and displays the image on the display device. The image processing includes, for example, resolution conversion, color correction processing, and projection surface shape correction processing in a projection-type image display device.

  Among these image processes, a process (hereinafter referred to as linear) that is desirably performed on an image signal on the assumption that the intensity of light emitted from the image display device (referred to as a luminance level) and the signal level are proportional to each other is assumed. Called processing). Patent Document 1 discloses a technique for improving the visibility of a moving image when dividing a frame into two subframes to display the frame frequency twice. Specifically, the high-frequency component of one frame is concentrated in the first subframe and the low-frequency component is distributed and displayed in the first and second subframes, thereby reducing motion blur and reducing flicker. It is suppressed. At this time, the calculation of the frequency component and the distribution degree to each subframe are defined with respect to the luminance level.

JP 2010-160440 A

  When linear processing is performed, the input image signal level is once converted into a luminance level. Since the input image signal level and the luminance level have a non-linear relationship, the bit accuracy after conversion necessary to maintain the step of the input image signal level even after conversion to the luminance level is larger than the input image signal level. Become. That is, the bit accuracy required for the linear processing is larger than that for processing on the input image signal level, and the circuit scale required for the image processing can be increased.

  Further, it is known that a general input image signal such as a TV image and a luminance level have a characteristic of a power of 2.2 from the characteristic of a CRT. The characteristic of the power of 2.2 has a slope that becomes smaller as it is closer to the 0 level (origin). Therefore, when converting the image signal level having the power of 2.2 to the luminance level, the gradation of the low gradation part of the image signal level is deteriorated if the bit accuracy after the conversion is not sufficient. As a result, the image quality may be deteriorated such that the low gradation portion is crushed in black and visually recognized.

  The present invention has been made in view of these problems, and provides an image processing technique capable of achieving both suppression of image quality deterioration in a low gradation portion and suppression of increase in circuit scale when performing linear processing. .

  One embodiment of the present invention relates to an image processing apparatus. In this image processing apparatus, the first gradation region, the second gradation region, and the third gradation region of the image signal corrected with respect to the response characteristic of the display are respectively converted into the first conversion characteristic, the second conversion characteristic, and the third conversion characteristic. Accordingly, conversion means for performing conversion according to the above and processing means for processing a conversion signal obtained as a result of conversion by the conversion means are provided. The first gradation region is lower than the third gradation region, and the second gradation region is between the first gradation region and the third gradation region, and the third conversion characteristic is a response characteristic. Correspondingly, the first conversion characteristic is linear, and the second conversion characteristic is determined so as to smoothly connect the first conversion characteristic and the third conversion characteristic in the second gradation range.

  According to the present invention, it is possible to achieve both suppression of image quality deterioration in a low gradation part and suppression of increase in circuit scale when performing linear processing.

FIG. 1A is a schematic diagram showing a flow of processing for an image signal in the image processing method according to the first embodiment, and FIG. 1B is a diagram showing an example of response characteristics of a display. FIGS. 2A and 2B are block diagrams illustrating functions and configurations of the image processing apparatuses according to the first and second embodiments, respectively. 3A is a diagram for explaining conversion characteristics in the gamma conversion unit, FIG. 3B is a diagram showing conversion characteristics in the gamma conversion unit, and FIG. 3C is a diagram explaining conversion characteristics in the degamma conversion unit. FIG. 3D is a diagram illustrating conversion characteristics in the degamma conversion unit. The figure which shows an example of the hardware constitutions of the image processing apparatus of Fig.2 (a). The flowchart which shows an example of a series of processes in the image processing apparatus of Fig.2 (a).

  Embodiments of the present invention will be described below with reference to the drawings. However, embodiments of the present invention are not limited to the following embodiments. The same or equivalent components, members, processes, and signals shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. In addition, in the drawings, some of the members that are not important for explanation are omitted.

(First embodiment)
FIG. 1A is a schematic diagram showing a flow of processing on an image signal in the image processing method according to the first embodiment. The image signal is generated by an imaging apparatus 10 such as a digital camera, a video camera, or a scanner, and is input to a display 14 such as a CRT monitor, a liquid crystal monitor, or a TV receiver through an image processing 12.

  FIG. 1B is a diagram illustrating an example of the response characteristic 18 of the display 14. FIG. 1B schematically shows a response characteristic 18 in which the horizontal axis is the level of the image signal and the vertical axis is the intensity of light emitted from the display 14 (brightness and luminance level). Normalization is performed with the minimum level of each axis being 0.0 and the maximum level being 1.0. Generally, it is known that the luminance level is proportional to γ = about 2.2 to the image signal level, and this response characteristic is called a gamma characteristic. In particular, a CRT used in a television receiver or the like has a gamma characteristic of γ = about 2.2.

  When an image signal (hereinafter referred to as an image signal in a luminance linear space) on the assumption that the luminance level is proportional to the image signal level is input to the display 14 as it is, the screen becomes dark due to the gamma characteristic of the display 14. Therefore, for many video signals and image signals including TV broadcasts, correction is generally performed to increase the level of the image signal in the luminance linear space in advance so as to cancel the gamma characteristic of the display 14. In particular, gamma correction for raising the level of the image signal in the luminance linear space to the power of (1 / γ) is often performed.

  The image signal generated by the imaging device 10 is subjected to gamma correction 16 so that it can be displayed naturally on a standard display. A liquid crystal display device may have a response characteristic different from that of a CRT, but is generally designed to have a gamma characteristic of γ = about 2.2 to suit display of a gamma-corrected image signal. Is.

  The image processing 12 corrects the characteristics of the display 14 such as color adjustment and brightness adjustment by the user and unevenness correction processing, and corrects the shape of the projection surface when the display 14 is a projection-type video display device. And a keystone correction process. Among these image processes, there is an image process that is desirably performed in a luminance linear space. For example, there is a case where the frame frequency is doubled and displayed by distributing the luminance of one frame input at 60 Hz to two sub-frames of 120 Hz. Assume that the image signal level of one frame is 0.5, and this is distributed and displayed in 0.2 and 0.8. In the image signal level, the level for two subframe periods is 1.0 (= 0.2 + 0.8) in total, which is equal to the case of no distribution (0.5 + 0.5). On the other hand, in terms of the luminance level, the luminance level is not linear with the image signal level as shown in FIG. 1B, and therefore, there is a deviation in the luminance level for two subframe periods. Therefore, it is desirable that such image processing is performed in a luminance linear space.

  Therefore, in the image processing 12 according to the present embodiment, the gamma-corrected image signal input from the imaging device 10 is subjected to gamma processing, and an image signal whose luminance level is approximately proportional to the image signal level (hereinafter referred to as luminance approximation). (Referred to as linear space image signal). Image processing is performed on the converted image signal, and degamma processing, which is the reverse processing of the gamma processing, is performed. The image signal after the degamma processing is output to the display 14. Accordingly, image processing that is desirably performed in the luminance linear space can be performed in the luminance approximate linear space.

  In an ideal situation, for example, in a situation where a sufficiently large bit accuracy is always available in image processing, gamma processing may be performed by converting an image signal according to conversion characteristics equivalent to gamma characteristics. That is, conversion is performed such that the horizontal axis shown in FIG. 1B is the image signal level input to the gamma processing (after normalization) and the vertical axis is the output level from the gamma processing (after normalization). . This conversion is realized using, for example, a lookup table. The converted image signal obtained as a result belongs to the luminance linear space.

  On the other hand, when the gamma characteristic γ = about 2.2 is used as it is in the gamma processing, the inclination near the origin becomes small as shown in FIG. That is, in order to sufficiently express the gamma characteristic γ = about 2.2, the number of output bits of gamma processing increases. For this reason, there are problems that the number of bits required for image processing increases and the circuit scale increases. In this case, the number of bits handled in gamma processing and degamma processing also increases. In response to these problems, if the number of output bits of the gamma processing is simply reduced, the low gradation part is crushed, the gradation is deteriorated, and the image quality is deteriorated.

  Therefore, in the gamma processing according to the present embodiment, different conversion characteristics are applied to each of the low gradation region, middle gradation region, and high gradation region of the image signal. The conversion characteristics of the low gradation range (referred to as low-frequency conversion characteristics) are linear, and an output level that is proportional to the input level is generated. High gradation range conversion characteristics (referred to as high-frequency conversion characteristics) correspond to gamma characteristics. The conversion characteristics of the medium gradation range between the low gradation range and the high gradation range (referred to as the mid-range conversion characteristic) is to smoothly connect the low-frequency conversion characteristic and the high-frequency conversion characteristic in the middle gradation range. It is determined. As a result, the image signal in the high gradation region is converted into an image signal in the luminance linear space, and the decrease in gradation due to gamma processing is suppressed or eliminated in the low gradation region. Therefore, both the conversion to the luminance approximate linear space and the suppression of the image quality deterioration of the low gradation part can be achieved without increasing the number of bits in the image processing after the gamma processing. As a result, an increase in circuit scale can be suppressed.

  FIG. 2A is a block diagram illustrating the function and configuration of the image processing apparatus 100 according to the first embodiment. The image processing apparatus 100 acquires a gamma-corrected image signal composed of three color components of R, G, and B, performs various color adjustments and image processing on the acquired image signal, and then displays the display device 104. Is displayed. The image processing apparatus 100 includes a gamma conversion unit 101, an image processing unit 102, a degamma conversion unit 103, a display device 104 such as a CRT monitor or a liquid crystal monitor, and a determination unit 105.

The gamma conversion unit 101 acquires a gamma-corrected image signal. The gamma conversion unit 101 converts the low gradation region, middle gradation region, and high gradation region of the acquired image signal according to the low region conversion characteristic, middle region conversion characteristic, and high region conversion characteristic, respectively. The low frequency conversion characteristic is a conversion characteristic that places importance on the gradation of the image signal level in the low gradation region, and the slope of the low frequency conversion characteristic is determined based on the bit accuracy in the image processing unit 102. In a simple example, assuming that the bit accuracy of the image signal input to the gamma conversion unit 101 is IN, and the bit accuracy of the conversion signal output from the gamma conversion unit 101 is OT, the low-frequency conversion characteristic is the first order of y = ux. It is expressed by a formula. Here, the inclination u is expressed by the following equation (1). It is assumed that IN ≦ OT, and u = 1 if IN> OT.
u = 1/2 ^OT-IN Formula (1)
Based on equation (1), the low gradation part of the converted signal is not crushed and the gradation is maintained.

  The determining unit 105 determines the slope u of the low-frequency conversion characteristics according to the processing in the image processing unit 102. The determination unit 105 acquires the bit accuracy (= bit accuracy OT of the converted signal output from the gamma conversion unit 101) used in the image processing in the image processing unit 102 from the image processing unit 102. The determination unit 105 calculates the slope u by the above equation (1) based on the acquired bit accuracy OT and the bit accuracy IN of the image signal that is given in advance.

FIG. 3A is a diagram for explaining the conversion characteristics in the gamma conversion unit 101. In FIG. 3A, the horizontal axis represents the level of the input image signal, and the vertical axis represents the level of the converted signal after conversion. A curve indicated by reference numeral 301 conforms to the gamma characteristic shown in FIG. 1B, and represents y = ^xγ . A straight line denoted by reference numeral 302 represents y = ux using u represented by the above formula (1). Here, the bit accuracy IN = 10 (bits) of the input image signal and the bit accuracy OT = 12 (bits) of the conversion signal output from the gamma conversion unit 101 are set. A black point indicated by reference numeral 303 is an intersection of the curve 301 and the straight line 302 other than the origin.

  When the straight line 302 is applied to the low gradation side of the intersection 303 and the curve 301 is applied to the high gradation side of the intersection 303, the intersection 303 becomes an inflection point. That is, the first derivative of the conversion characteristic becomes discontinuous at the intersection 303. In this case, the image quality may be deteriorated. Therefore, the determination unit 105 includes a first characteristic change point 304 that is a point on the straight line 302 on the low gradation side of the intersection 303 and a second characteristic change point 305 that is a point on the curve 301 on the high gradation side of the intersection 303. And select. The determination unit 105 determines the image signal level range from the origin to the first characteristic change point 304 as the low gradation region 307 of the image signal. The determination unit 105 determines the range of the image signal level from the first characteristic change point 304 to the second characteristic change point 305 as the intermediate gradation region 308 of the image signal. The determination unit 105 determines the range of the image signal level from the second characteristic change point 305 to the maximum value as the high gradation region 309 of the image signal. The determination unit 105 determines the characteristic represented by the straight line 302 with respect to the low gradation area 307 as the low-frequency conversion characteristic. The determination unit 105 determines the characteristic represented by the curve 301 for the high gradation region 309 as the high-frequency conversion characteristic.

  The determining unit 105 performs Bezier interpolation using the three points of the intersection point 303, the first characteristic change point 304, and the second characteristic change point 305, and obtains a Bezier curve 310 for the intermediate gradation region 308. FIG. 3B is a diagram illustrating the conversion characteristics 306 in the gamma conversion unit 101. The conversion characteristic 306 of the gamma conversion unit 101 is different in each of the three sections of the low gradation area 307, the medium gradation area 308, and the high gradation area 309, but there is no inflection point including the boundary of the section. The interpolation is not limited to Bezier interpolation, and other interpolation methods such as spline interpolation may be used. Further, in the vicinity of the inflection point, two conversion characteristics of a low frequency band and a high frequency band may be synthesized at an arbitrary ratio, but it is desirable that the low frequency conversion characteristics and the local inclination are the same or larger.

  For example, the determination unit is configured so that the ratio between the lateral distance R1 between the intersection 303 and the first characteristic change point 304 and the lateral distance R2 between the intersection 303 and the second characteristic change point 305 becomes a predetermined ratio. 105 may determine a first characteristic change point 304 and a second characteristic change point 305. In Bezier interpolation, the lateral distance R1 between the intersection 303 and the first characteristic change point 304 corresponds to the degree of contribution from the low-frequency conversion characteristics to the mid-frequency conversion characteristics. The lateral distance R2 between the intersection 303 and the second characteristic change point 305 corresponds to the degree of contribution from the high-frequency conversion characteristics to the mid-range conversion characteristics. Therefore, in this case, the determination unit 105 determines the mid-range conversion characteristics by combining the low-frequency conversion characteristics and the high-frequency conversion characteristics at a predetermined ratio. In addition, this ratio may be realized by weighting or the like so that the contribution from the low-frequency conversion characteristics is greater than the contribution from the high-frequency conversion characteristics on the low gradation side of the middle gradation area.

  As described above, according to the conversion characteristic 306 shown in FIG. 3B, the gradation is maintained without collapsing the low gradation region. In addition, the image signal level that is larger than the image signal level corresponding to the second characteristic change point 305, except for the low gradation range, is converted by γ = about 2.2. Processed in space. Thereby, the gamma conversion unit 101 can realize conversion to the luminance approximate linear space while suppressing the phenomenon that the low gradation region is crushed, the gradation property is deteriorated, and the image quality is deteriorated.

  Returning to FIG. 2A, the image processing unit 102 performs the image processing described in relation to the image processing 12 shown in FIG. 1 on the conversion signal obtained as a result of the conversion by the gamma conversion unit 101. Since the signal output from the gamma conversion unit 101 is an image signal in a luminance approximate linear space, the image processing unit 102 can cope with image processing that is desirably performed in the luminance linear space. The image processing unit 102 outputs the signal after image processing to the degamma conversion unit 103.

  The degamma conversion unit 103 is an inverse conversion unit that converts an output signal obtained as a result of processing by the image processing unit 102 according to the inverse characteristic of the conversion characteristic in the gamma conversion unit 101. FIG. 3C is a diagram for explaining the conversion characteristics in the degamma conversion unit 103. In FIG. 3C, the horizontal axis represents the signal level after image processing, and the vertical axis represents the signal level output from the degamma conversion unit 103. Here, the bit accuracy of the signal after image processing = bit accuracy OT = 12 (bits) of the conversion signal output from the gamma conversion unit 101, the level of the signal output from the degamma conversion unit 103 = input to the gamma conversion unit 101 The bit accuracy of the image signal is IN = 10 (bits).

A curve indicated by reference numeral 321 is an inverse function of the curve 301 shown in FIG. 3A and represents y = x ^{1 / γ} . A straight line indicated by reference numeral 322 is an inverse function of the straight line 302 shown in FIG. 3A and represents y = (1 / u) x. A black point indicated by reference numeral 323 is an intersection point of the curve 321 and the straight line 322 other than the origin. A white point indicated by reference numeral 324 corresponds to the first characteristic change point 304, and a white point indicated by reference numeral 325 corresponds to the second characteristic change point 305. FIG. 3D is a diagram illustrating the conversion characteristics 326 in the degamma conversion unit 103. This conversion characteristic 326 is a reverse characteristic of the conversion characteristic 306 of the gamma conversion unit 101 shown in FIG.

  By the degamma processing by the degamma conversion unit 103, the signal after image processing in the luminance approximate linear space returns to the gamma-corrected image signal. Various image processing may be performed in a further stage of the degamma conversion unit 103. The signal output from the degamma conversion unit 103 is input to the display device 104 via a VT conversion unit, a display device driving unit, and the like (not shown).

  At least a part of each functional unit of the image processing apparatus 100 illustrated in FIG. 2A may be realized as an independent apparatus. Moreover, you may implement | achieve as software which implement | achieves each function. In the present embodiment, it is assumed that each unit excluding the display device 104 is realized by software. Hereinafter, an example of hardware for realizing each functional unit of the image processing apparatus 100 described above by software will be described.

  FIG. 4 is a diagram illustrating an example of a hardware configuration of the image processing apparatus 100 in FIG. The CPU 201 mainly controls the operation of each component. The main memory 202 stores a control program executed by the CPU 201 and provides a work area when the CPU 201 executes the program. The magnetic disk 203 is an example of an external storage device that stores an operating system (OS), a device driver for peripheral devices, and a computer program such as a program for realizing the image processing method according to the present embodiment. When the CPU 201 executes a program stored in the main memory 202 and the magnetic disk 203, the functions (software) of the image processing apparatus 100 shown in FIG. Note that the program stored in the magnetic disk 203 is expanded in the main memory 202 as necessary, and is executed by the CPU 201.

  The display memory 204 temporarily stores display data. The display device 104 displays an image, text, or the like based on data from the display memory 204. A mouse 206 and a keyboard 207 perform pointing input and character input by the user, respectively. The above components are connected to each other via a common bus 208 so that they can communicate with each other.

  FIG. 5 is a flowchart illustrating an example of a series of processes in the image processing apparatus 100. In S501, the high frequency conversion characteristic is determined according to the gamma characteristic, and the low frequency conversion characteristic is determined based on the equation (1). In S502, the intersection other than the origin of the low-frequency conversion characteristic and the high-frequency conversion characteristic is acquired. In S503, the first characteristic change point 304, which is lower than the image signal level corresponding to the intersection and on the low-frequency conversion characteristics, and the point higher than the image signal level corresponding to the intersection and on the high-frequency conversion characteristics. Two points of a certain second characteristic change point 305 are determined. Using these two points, a conversion characteristic between the two points is calculated as a mid-range conversion characteristic by Bezier interpolation centering on the intersection. In step S504, the conversion characteristics of the gamma conversion are determined by sequentially applying the low-frequency conversion characteristics from the origin, the mid-range conversion characteristics calculated by Bezier interpolation, and the high-frequency conversion characteristics.

  According to the image processing apparatus 100 according to the present embodiment, an image signal in a high gradation region is converted into an image signal in a luminance linear space, and a decrease in gradation due to gamma conversion is suppressed or removed in a low gradation region. Is done. Therefore, both the conversion to the luminance approximate linear space and the suppression of the image quality deterioration of the low gradation part can be achieved without increasing the number of bits in the image processing after the gamma conversion. As a result, an increase in circuit scale can be suppressed.

  In the above formula (1), IN is bit precision of the input image signal, but is not limited thereto. For example, as a result of measuring the luminance level, if the luminance level of the low gradation portion that can be expressed by the target display device 104 is smaller than the bit accuracy of the image signal, the expressible bit accuracy is applied to IN. Also good. Thereby, it is possible to suppress a decrease in gradation of the low gradation part by the gamma conversion unit 101, and an image signal level range (that is, a high gradation area) converted by the high frequency conversion characteristic is widened. The image quality can be further improved. In the above description, the luminance level of the low gradation part that can be expressed is measured. However, a level that can be visually recognized by the user or the evaluator may be used, or an acceptable level may be used. .

  Further, when the bit precision used in the image processing in the image processing unit 102 is variable in order to reduce the power consumption, reduce the bandwidth during DRAM access, or the like, the OT may be changed accordingly. Thereby, it is possible to adaptively suppress a decrease in gradation in the low gradation part.

  Further, the image signal is composed of three color components of R, G, and B, and is input for each pixel, and the gamma conversion unit 101 may independently convert each color component. The characteristic representing the relationship between the image signal level and the luminance level may be about 2.2 (γ = about 2.2) for each color component. When this characteristic fluctuates with time, it may be corrected by the degamma conversion unit 103 shown in FIG.

  In the “luminance linear space”, it is desirable that the image signal level and the luminance level are proportional, but there may be an error within about 5%. In addition, a linear expression based on the slope u shown in Expression (1) is adopted as the low-frequency conversion characteristic with an emphasis on gradation, but the present invention is not limited to this and suppresses a decrease in gradation in the low gradation area. The conversion characteristics may be calculated as appropriate.

(Second Embodiment)
In the second embodiment, the image processing apparatus is provided with an analysis unit 602 for analyzing an image signal and determining a conversion characteristic suitable for the analysis result. FIG. 2B is a block diagram illustrating the function and configuration of the image processing apparatus 600 according to the second embodiment. The image processing apparatus 600 includes a gamma conversion unit 101, an image processing unit 102, a degamma conversion unit 103, a display device 104, a determination unit 601 and an analysis unit 602.

  The analysis unit 602 analyzes the input gamma-corrected image signal and calculates a feature amount. The determination unit 601 determines the slope of the low-frequency conversion characteristic according to the feature amount calculated by the analysis unit 602. Further, the determination unit 601 sets the ratio of the combination of the low-frequency conversion characteristic and the high-frequency conversion characteristic based on the feature amount calculated by the analysis unit 602.

  For example, the analysis unit 602 obtains a histogram. The histogram here is the appearance frequency (number of pixels) for each image signal level in one frame image. The determination unit 601 changes the composition ratio of the low-frequency conversion characteristics and the high-frequency conversion characteristics, or the slope shown in Expression (1), according to the histogram obtained for each color component by the analysis unit 602. In the histogram obtained by the analysis unit 602, the determination unit 601 reduces the low frequency of the gamma conversion unit 101 so that the lower the frequency of the low gradation level, the smaller the slope of Equation (1) becomes (closer to 0). Control conversion characteristics. Thereby, the range of the image signal level processed with the high frequency conversion characteristic can be expanded, and therefore the range of the image signal that can be processed in the luminance linear space can be expanded.

  For example, the determination unit 601 determines that the minimum level taken by the histogram, or the maximum level at which a pixel within 5% of the parameter exists from the minimum level is the intersection of the low-frequency conversion characteristics and the high-frequency conversion characteristics (FIG. 3A). The slope v of the low-frequency conversion characteristic is calculated so as to be the intersection 303). The determination unit 601 may select the smaller value of the calculated slope v and the slope u calculated by Expression (1).

  The above-described determination method from the histogram is an example. Depending on whether or not the center of gravity of the histogram is larger than a predetermined threshold, the frequency of the low gradation level may be roughly determined, or any other method may be used. Instead of obtaining a histogram for each color component, any one of RGB (for example, G) may be used, or a luminance component (Y) may be calculated from the color component to obtain a luminance component histogram. A histogram may be calculated and applied to each region in the image instead of one frame image. In addition, a histogram of a plurality of frame images may be applied by weighted averaging for the purpose of giving continuity to the moving image. Although it is desirable to count the appearance frequency of all pixels, only a part of the pixels may be used in order to reduce the circuit scale necessary for histogram acquisition and analysis.

In addition to the above histogram, examples of feature amounts calculated by analyzing the image signal in the analysis unit 602 include the following.
The analysis unit 602 determines the bit depth of the image signal by analyzing whether or not the lower bits of the input image signal vary. The determination unit 601 sets the bit depth, which is the determination result in the analysis unit 602, to IN in Expression (1). Thereby, for example, an interface or a format that can transmit an image up to 10 bits, but when an input image signal itself is 8 bits, IN = 8 is set. As a result, the range of image signal levels that can be processed in the luminance linear space can be expanded.

  The function examples of the determination unit 601 and the analysis unit 602 have been described above. However, in the degamma conversion unit 103 provided at the subsequent stage of the video processing unit 102, the conversion process is performed with the reverse characteristic of the conversion characteristic in the gamma conversion unit 101.

  As described above, according to the image processing apparatus 600 according to the present embodiment, in addition to the effects obtained in the first embodiment, the range of the image signal level that can be processed in the luminance linear space by analyzing the image signal. Can be further expanded, and the image quality can be further improved.

  The configuration and operation of the image processing apparatus according to the embodiment have been described above. These embodiments are exemplifications, and it is understood by those skilled in the art that various modifications can be made to each component and combination of processes, and such modifications are within the scope of the present invention. .

(Other examples)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

  100 image processing apparatus, 101 gamma conversion unit, 102 image processing unit, 103 degamma conversion unit, 104 display device

Claims (13)

Conversion means for converting the first gradation region, the second gradation region, and the third gradation region of the image signal corrected with respect to the response characteristic of the display according to the first conversion characteristic, the second conversion characteristic, and the third conversion characteristic, respectively. When,
Processing means for processing a conversion signal obtained as a result of conversion by the conversion means,
The first gradation region is lower in gradation than the third gradation region, and the second gradation region is between the first gradation region and the third gradation region;
The third conversion characteristic corresponds to the response characteristic, the first conversion characteristic is linear, and the second conversion characteristic smoothly smoothes the first conversion characteristic and the third conversion characteristic in the second gradation range. An image processing apparatus that is determined to connect to   The image processing apparatus according to claim 1, wherein the slope of the first conversion characteristic is determined based on bit accuracy in the processing unit.   The image processing apparatus according to claim 1, further comprising a determination unit that determines a slope of the first conversion characteristic in accordance with processing in the processing unit or the image signal.   The said 2nd conversion characteristic is determined by synthesize | combining a said 1st conversion characteristic and a said 3rd conversion characteristic in a predetermined ratio, The one of Claim 1 to 3 characterized by the above-mentioned. Image processing device.   The ratio is set so that a contribution from the first conversion characteristic is larger than a contribution from the third conversion characteristic on a low gradation side of the second gradation range. The image processing apparatus described.   6. The image processing apparatus according to claim 1, wherein the response characteristic is a gamma characteristic of a display. Analyzing means for analyzing the image signal and calculating a feature quantity,
The image processing apparatus according to claim 3, wherein the determining unit determines an inclination of the first conversion characteristic according to the feature amount calculated by the analyzing unit. Analyzing means for analyzing the image signal and calculating a feature quantity,
The image processing apparatus according to claim 4, wherein the ratio is set based on the feature amount calculated by the analysis unit.   9. The apparatus according to claim 1, further comprising an inverse conversion unit configured to convert an output signal obtained as a result of the processing by the processing unit in accordance with an inverse characteristic of the conversion characteristic of the conversion unit. Image processing device. Converting the first gradation region, the second gradation region, and the third gradation region of the image signal corrected with respect to the response characteristic of the display according to the first conversion characteristic, the second conversion characteristic, and the third conversion characteristic, respectively; ,
Processing a converted signal obtained as a result of the conversion,
The first gradation region is lower in gradation than the third gradation region, and the second gradation region is between the first gradation region and the third gradation region;
The third conversion characteristic corresponds to the response characteristic, the first conversion characteristic is linear, and the second conversion characteristic smoothly smoothes the first conversion characteristic and the third conversion characteristic in the second gradation range. An image processing method characterized by being determined to connect to Analyzing the image signal to calculate a feature amount;
The image processing method according to claim 10, further comprising: determining an inclination of the first conversion characteristic in accordance with the calculated feature amount. Analyzing the image signal to calculate a feature amount;
Further determining the second conversion characteristic by combining the first conversion characteristic and the third conversion characteristic at a predetermined ratio;
The image processing method according to claim 10, wherein the ratio is set based on the calculated feature amount.   The program for functioning a computer as each means of the apparatus of any one of Claims 1 thru | or 9.