JP2010251883A - Image processor, image processing method, program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor with a highly accurate and simple configuration, having little epicritic deterioration in input image data. <P>SOLUTION: A lightness conversion portion 105 converts and outputs lightness of original image data into a lightness area of an image output device 103. A variation calculation portion 106 calculates variation of colors when a color in image data output by the lightness conversion portion 105 is converted into a color in a color reproduction range of the image output device. A variation correction portion 107 corrects variation so as to leave an edge and a low frequency component at an image plane of the variation. A color correction portion 108 corrects a color in the lightness converted image data, based on the corrected variation. A color conversion portion 109 converts the color corrected image data into a color in the color reproduction range of the image output device 103. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image processing method, a program, and a storage medium for converting input image data into image data within a color reproduction range of an image output apparatus such as a printer or a display.

  One type of image processing is gamut processing for converting the color of input image data into a color in the color reproduction range (color gamut, gamut) of the image output apparatus. Image output devices such as printers and displays cannot reproduce all colors that humans can perceive and can only reproduce a limited range of colors, but the image data itself has a relatively large color reproduction range. It is often expressible, and in some cases, all colors that can be perceived by humans can be expressed. Regardless of the color format of the image data, in any case, it is necessary to convert the color of the image data outside the color reproduction range of the image output apparatus into a reproducible color and enable output.

  Conventionally, various methods have been proposed regarding the problem of converting colors that cannot be reproduced by an image output device. Typical conversion methods include gradation preservation conversion method, hue preservation conversion method, saturation, and so on. There is a preservation conversion method.

  The gradation preservation conversion method is used not only for the color outside the color reproduction range of the image output device but also for the color within the color reproduction range toward the fixed point on the gray axis within the color reproduction range of the image output device while preserving the hue. It is a method of changing and compressing at a certain ratio. Since this method preserves color differences, it is suitable for gamut processing on images such as photographs that emphasize gradation. However, since the input image is compressed at a constant rate regardless of the color range of the input image, there is a disadvantage that the image is compressed to a range where compression is unnecessary. Further, since the color change itself is also compressed, there is a drawback that it is easy to become a sleepy image lacking power.

  On the other hand, with the hue preservation conversion method, the color reproduction of the image output device toward the fixed point on the gray axis within the color reproduction range of the image output device while keeping the hue for the color outside the color reproduction range of the image output device. It is a method of pasting to the outermost part of the range. This method is also suitable for photographic images because of its relatively natural reproduction.

  The saturation preserving conversion method is a method for converting a color outside the color reproduction range of the image output apparatus so that the lightness and the hue are not greatly changed while preserving the saturation as much as possible. Since the vividness of the image is maintained, it is suitable for gamut processing for images such as graphics and characters that place importance on color reproducibility. However, since these conversion methods change only the color outside the color reproduction range, if the converted color and its neighboring colors are present in the image data before conversion, the distinguishability with those colors deteriorates. There was a drawback of doing. In addition, the color that could be identified in the image data before conversion may be converted to the same outermost color, and the discrimination may be deteriorated.

  For this reason, image processing apparatuses and methods that compensate for these drawbacks have been proposed. For example, in the image processing method of Patent Document 1, a color conversion step for converting the color of input image data into a color within a predetermined color reproduction range, a color of the input image data, and a color conversion step are used for conversion. A color difference calculating step for calculating a difference from the color difference, a color difference filtering step for filtering the difference calculated by the color difference calculating step, and a color obtained by filtering the color converted by the color conversion step based on the difference filtered by the color difference filtering step. And a color correction step for correcting. In this method, information that disappears in the color conversion step is extracted in the color difference calculation step, and information relating to the distinguishability is extracted by filtering in the color difference filtering step. In the color correction step, the information relating to the extracted distinguishability is added to the color converted by the color conversion step, thereby preventing the deterioration of the distinguishability.

  However, since this method includes a possibility that the color of the image data output by the color correction step is outside the above-described predetermined color reproduction range, it is substantially converted to a color within the predetermined color reproduction range. A second color conversion step is required. For this reason, there has been a drawback in that the accumulation of quantization errors due to double processing for conversion to a color within a predetermined color reproduction range is large, and accuracy cannot be obtained. In addition, increasing the accuracy of each process for reducing the quantization error has the disadvantage that the processing load in image processing increases and the image processing apparatus becomes complicated.

  The image processing method according to Non-Patent Document 1 includes a compression rate calculation step for calculating a compression rate of a color gamut when the color of input image data is converted into a color within a predetermined color reproduction range, and a compression A filtering step for filtering the compression rate calculated by the rate calculating step, and a color conversion step for compressing the color gamut of the input image data based on the compression rate to which the filtering step applied filtering. . In this method, for example, color conversion based on the above-described hue preservation conversion method is used, and it is possible to improve the discrimination with respect to a specific direction toward a fixed point on the gray axis within the color reproduction range of the image output apparatus. However, the direction perpendicular to the above direction has a disadvantage that there is no effect and the discrimination cannot be improved.

  Furthermore, the image processing apparatus of Patent Literature 2 removes noise included in the correction amount calculated by the correction amount calculation unit that calculates the correction amount for converting the color of the input image data and the correction amount calculation unit. The noise removing unit and a color correcting unit that corrects the color of the input image data based on the correction amount from which the noise removing unit has removed the noise.

  In the image processing apparatus described above, the noise removal means is a one-dimensional filter in order to reduce the influence of noise received on the transmission path when enhancing the saturation and lightness of the image data. After calculating a correction amount that enhances the saturation and lightness of the data, the high-frequency component noise close to the pixel frequency is removed, and then the color of the image data is corrected to enhance the saturation and lightness. On the other hand, the gamut processing basically does not emphasize. In addition, the deterioration of the discriminability occurs because the change in the image data in the two-dimensional plane of the image is lost or compressed, so that it cannot be recovered even if the noise received on the transmission path is removed. There were drawbacks.

The present invention has been made in view of the above problems,
An object of the present invention (Claim 1) is an image processing apparatus that performs processing for converting input image data into image data within the color reproduction range of the image output apparatus, while having a high-precision and simple configuration. Another object of the present invention is to provide an image processing apparatus in which the input image data has little deterioration in identification.

  An object of the present invention (Claim 2) relates to the improvement of Claim 1 and is an image processing apparatus capable of reducing the deterioration of the discrimination of the image data in accordance with the attribute information of the input image data. It is to provide.

  An object of the present invention (Claim 3) relates to the improvement of Claim 1 or 2 and is an image processing apparatus capable of reducing the deterioration of discrimination while maintaining the hue of the color of the input image data. Is to provide.

  An object of the present invention (Claim 4) relates to the improvement of Claims 1 to 3, and provides an image processing apparatus having a simpler configuration and capable of reducing deterioration of discrimination. It is in.

  It is another object of the present invention (claim 5) to provide an image processing method that has a highly accurate and simple configuration and that has little deterioration in the discrimination of input image data.

  Another object of the present invention (claims 6 and 7) is to provide a program and a storage medium having a code for executing the image processing method according to claim 5.

  The present invention is an image processing apparatus that performs a process of converting input image data into image data within a color reproduction range of an image output apparatus, wherein the color of the input image data is a first color. The change amount calculating means for calculating the amount of change in color when converted to a color within the reproduction range, and at least the edges and low frequency components in the image plane of the change amount calculated by the change amount calculating means are left. A change amount correcting unit that corrects the target change amount calculated by the change amount calculating unit based on a change amount in the vicinity of the plane, and the input image based on the change amount corrected by the change amount correcting unit. The main features include at least color correction means for correcting the color of the data, and color conversion means for converting the color of the image data corrected by the color correction means into a color within the second color reproduction range. And

  Claim 1: An image processing apparatus for performing processing for converting input image data into image data within a color reproduction range of the image output apparatus, wherein the color of the input image data is a first color. The change amount calculating means for calculating the amount of change in color when converted to a color within the reproduction range, and at least the edges and low frequency components in the image plane of the change amount calculated by the change amount calculating means are left. A change amount correcting unit that corrects the target change amount calculated by the change amount calculating unit based on a change amount in the vicinity of the plane, and the input image based on the change amount corrected by the change amount correcting unit. An image having at least color correction means for correcting the color of the data and color conversion means for converting the color of the image data corrected by the color correction means into a color within the second color reproduction range In the processing unit, Since the color of the input image data is corrected based on the amount of change corrected so as to leave the edge and the low frequency component in the plane, and converted into a color within the second color reproduction range of the image output device or the like Thus, it was possible to realize an image processing apparatus that has a high accuracy and a simple configuration and has little deterioration in the discrimination of input image data.

  According to a second aspect of the present invention, there is provided attribute information setting means for setting attribute information of the input image data, and the change amount calculating means calculates a color change amount based on the attribute set by the attribute information setting means. The image processing apparatus according to claim 1, wherein the color change amount can be calculated according to the attribute information of the input image data, and therefore, according to the attribute information of the input image data. Thus, an image processing apparatus capable of further reducing the deterioration of the image data identification can be realized.

  According to a third aspect of the present invention, the change amount calculation unit calculates a color change amount when the color of the input image data is held and converted into a color within the first color reproduction range. The image processing apparatus according to claim 1 or 2, wherein the hue of the color of the input image data can be held, so that the distinctiveness is deteriorated while the hue of the color of the input image data is held. An image processing apparatus that can be reduced has been realized.

  A fourth aspect of the present invention includes: a low-resolution conversion unit that reduces the resolution of the image data; and a resolution restoration unit that restores the resolution of the image data in response to the low-resolution conversion unit. A color change amount is calculated when the color of the input image data processed by the low resolution conversion means is converted into a color within the first color reproduction range, and the color correction means is configured to restore the resolution. 4. The image processing according to claim 1, wherein a color of the input image data is corrected based on a change amount corrected by the change amount correction unit processed by the unit. 5. In the apparatus, since the change amount calculating means and the change amount correcting means can handle image data or change amounts with a reduced resolution, it is possible to reduce deterioration of discrimination with a simpler configuration. It was possible to realize an image processing apparatus.

  Claim 5: An image processing method for performing a process of converting input image data into image data within a color reproduction range of an image output device, wherein the color of the input image data is a first color. A change amount calculation step for calculating a color change amount when converted to a color within the reproduction range, and at least an edge in the image plane of the change amount calculated by the change amount calculation step and a low frequency component are left. A change amount correcting step for correcting the target change amount calculated by the change amount calculating step based on a change amount in the vicinity of the plane, and the input image based on the change amount corrected by the change amount correcting step. An image comprising at least a color correction step for correcting the color of the data, and a color conversion step for converting the color of the image data corrected by the color correction step into a color within the second color reproduction range In the processing method, Since the color of the input image data is corrected based on the amount of change corrected so as to leave the edge and the low frequency component in the plane, and converted into a color within the second color reproduction range of the image output device or the like Thus, it was possible to realize an image processing method that has a high accuracy and a simple configuration, and has little deterioration in the discrimination of the input image data.

  Claim 6: A program for causing a computer to implement the image processing method according to claim 5 can be realized.

  Claim 7: A computer-readable recording medium on which a program for causing a computer to implement the image processing method according to claim 5 is recorded.

1 shows a configuration of an image processing system according to a first embodiment. It is a figure explaining the lightness conversion by a lightness conversion part. The structure of a lightness conversion part is shown. An example of correction when the maximum lightness and the minimum lightness of the output gamut are not achromatic is shown. It is a figure explaining the hue preservation | save conversion method. The structure of a variation | change_quantity calculation part is shown. It is a figure explaining the correction by the variation correction part. It is a figure explaining the process which a variation | change_quantity correction part implements. 2 shows a configuration of an image processing system according to a second embodiment. 3 shows a configuration of an image processing system according to a third embodiment. 9 is a process flowchart according to an image processing method of Embodiment 4.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of an image processing system according to a first embodiment of the present invention. In FIG. 1, 101 is an image input device, 102 is an image processing device, and 103 is an image output device. The image input device 101 is, for example, a digital still camera that shoots a landscape or a person and stores it as image data, a color scanner that scans a document or the like to generate image data, or a storage medium that stores the above-described image data or the like ( For example, an auxiliary storage device (storage) including a control unit that controls reading and writing of the storage medium corresponds to an SD memory, a hard disk drive, and the like, and image data (hereinafter referred to as original image data) is transferred to the image processing device 102. It is a device that outputs. Here, the original image data output from the image input apparatus 101 has its color specification format specified by an ICC profile embedded in the original image data, communication between the image input apparatus 101 and the image processing apparatus 102, or the like. It is assumed that Alternatively, a standard color specification format such as sRGB or Adobe (registered trademark) RGB may be implicitly determined as the color specification format. In any case, the image input apparatus 101 outputs original image data in which the color specification format is determined to the image processing apparatus 102. In the following description, it is assumed that a digital still camera is used as the image input device 101 and Adobe RGB is determined by communication as the color format of the original image data, but the present invention is not limited to this.

  The image processing apparatus 102 performs processing such as converting original image data from the image input apparatus 101 that exceeds the color gamut that the image output apparatus 103 can output into the color gamut of the image output apparatus 103.

  The image output device 103 corresponds to, for example, an LCD display that displays image data on a screen, a color printer that records image data on a recording medium such as paper, and the like. This is a device that visualizes and outputs output image data. In the following, an example in which a color printer is used as the image output apparatus 103 will be described, but the present invention is not limited to this.

  The image processing apparatus 102 includes a color conversion unit 104, a lightness conversion unit 105, a change amount calculation unit 106, a change amount correction unit 107, a color correction unit 108, a color conversion unit 109, and the like.

  Here, in the image processing apparatus 102 of the present embodiment, the color of the image data is mainly handled by the LCh color value. The LCh color specification value is a value obtained by converting the CIELAB color specification value into a cylindrical coordinate system. That is, as described above, in the present embodiment, since the original image data having the colorimetric format AdobeRGB is input, the colorimetric conversion unit 104 converts the color of the input image data into CIELAB colorimetric values, and further the cylinder. A process of converting to the coordinate system (LCh1) is performed.

Specifically, assuming that the 8-bit pixel values of AdobeRGB are R ′ ₈ , G ′ ₈ , and B ′ ₈ ,

によって、ＣＩＥＸＹＺ（Ｄ５０）に変換し、

To convert to CIEXYZ (D50),

によって、ＣＩＥＬＡＢ（Ｄ５０）に変換し、

To convert to CIELAB (D50),

によって、Ｃｈに変換する。

To convert to Ch.

Further, the lightness conversion unit 105 converts the lightness of the original image data into the lightness region of the image output device 103 based on the lightness region in which the original image data can be expressed and the lightness region in which the image output device 103 can output. This is a block for outputting (LCh2). Here, the brightness range that can represent the original image data is determined by the above-described color specification format. For example, in Adobe RGB, the lightness L ^* = 0 to 100. Further, the brightness range that can be output by the image output apparatus 103 is determined by the color gamut that can be output by the image output apparatus 103. For example, in a color printer, the upper limit of the brightness range is determined by the recording medium used in the color printer, and the lower limit of the brightness range is determined by the brightness when composite black or the like is recorded on the recording medium.

  In this embodiment, the color gamut that can be output by the image output apparatus 103 is notified from the image output apparatus 103 to the image processing apparatus 102 by communication, and the color conversion is performed from the color gamut that can be output by the image output apparatus 103. The unit 105 extracts the brightness range that can be output, that is, the upper and lower limits of the brightness, and uses them for the brightness conversion.

  The communication of the color gamuts that can be output by the image output apparatus 103 is not limited to this, and may be notified using a method such as directly supplying the ICC profile of the image output apparatus 103 to the image processing apparatus 102, for example.

  Next, the conversion performed by the lightness conversion unit 105 will be described with reference to FIG. FIG. 2A is a cross-sectional view of the LCh color space cut along the brightness axis, and shows an example of the relationship between the color gamut that can represent the original image data and the color gamut that the image output apparatus 103 can output. As shown in the figure, the color gamut that can represent the original image data is generally larger than the color gamut that the image output device 103 can output, and the range in the lightness axis direction (lightness range) is often in an inclusive relationship. . For this reason, the lightness conversion unit 105 compresses and converts the lightness range of the original image data within the lightness range of the image output device 103, and smoothes the lightness of the image data (hereinafter referred to as lightness converted image data) by the image output device. To be able to reproduce.

  The solid line in FIG. 2B shows an example of the brightness conversion characteristic. The brightness range that can be expressed by the original image data is linearly converted with respect to the brightness range that can be output by the image output device 103. Yes.

  FIG. 2C shows the relationship between the color gamut that can express the image data (lightness conversion image data) after the above-described conversion and the color gamut that the image output device 103 can output. A state in which the brightness of the original image data is converted within the brightness range of the output device 103 is shown.

  In the above description, the lightness conversion is performed linearly. However, the present invention is not limited to this as long as the upper and lower limits of the lightness range coincide and the middle is simply increased. For example, an S-shaped non-linear transformation such as a broken line in FIG. 2B may be used.

  A detailed block diagram of the brightness conversion unit 105 as described above is shown in FIG. In FIG. 3, reference numeral 301 denotes a 1DLUT (one-dimensional look-up table), which converts the lightness of the original image data using a one-dimensional table describing the lightness conversion characteristics as shown in FIG.

In addition, for the sake of easy explanation, the maximum brightness and the minimum brightness that can represent the original image data, and the maximum brightness and the minimum brightness that can be output by the image output device 103 are each achromatic (C ^* = 0). Although an example is shown, the present invention is not limited to this. For example, as shown in FIG. 4A, when the maximum brightness (point 401) that can be output by the image output apparatus 103 is not achromatic (C ^* ≠ 0), an achromatic color (point 402) having the same brightness is used. Therefore, the maximum lightness point that can be output is corrected with the chromaticity correction amount (Δa ^* , Δb ^* ). The color gamut that can be output by the image output device 103 can be handled in the same manner by weighting the chromaticity correction amount according to the lightness and correcting the color gamut that can be output. Further, as shown in FIG. 4B, when the minimum lightness (point 403) that can be output by the image output apparatus 103 is not achromatic (C ^* ≠ 0), the point (point 404) is regarded as the minimum lightness that can be output by the image output apparatus 103, it can be handled similarly.

  Referring to FIG. 1 again, the change amount calculating unit 106 changes the color change amount (ΔLCh1) when the color of the image data output from the lightness conversion unit 105 is converted into a color within a predetermined color reproduction range. Is a block for calculating. Here, the predetermined color reproduction range is, for example, the color reproduction range of the image output device 103 described above or a color reproduction range obtained by correcting the color reproduction range. Further, as the conversion method at that time, for example, the above-described typical conversion method can be used. In the following, a case where the hue preservation conversion method is used will be described as an example, but the present invention is not limited to this.

  FIG. 5 is an explanatory diagram of the hue preservation conversion method. FIG. 5 is a cross-sectional view of the LCh color space cut along the lightness axis, and shows an example of the relationship between the color gamut that can express image data after lightness conversion and the color gamut that the image output device 103 can output. Here, since it is cut along the lightness axis, two hue planes with the lightness axis as a boundary are displayed. In the hue preservation conversion method, only the color outside the color reproduction range of the image output device is stored in the color reproduction range of the image output device toward the fixed point on the gray axis within the color reproduction range of the image output device while keeping the hue. This is a method of pasting to the outermost shell. In the example of FIG. 5, a point on the gray axis having the same brightness as the highest saturation point in each hue of the color reproduction range of the image output apparatus is used as the fixed point on the gray axis. That is, it is pasted on the outermost part of the color reproduction range of the image output device toward the point 502 on the gray axis with respect to the highest saturation point 501 and the point 504 on the gray axis with respect to the highest saturation point 503. Accordingly, the brightness-converted image data 505 is pasted on the outermost contour 506 of the color reproduction range of the image output apparatus. Further, the brightness-converted image data 508 is pasted on the outermost contour 509 of the color reproduction range of the image output apparatus. A change amount corresponding to the image data 505 after brightness conversion is a vector indicated by 507, and a change amount corresponding to the image data 508 after brightness conversion is a vector indicated by 510. In the hue preservation conversion method, since the pasting is performed while the hue is preserved, the change amount indicated by the vector 507 or 510 does not have a component corresponding to the hue difference, and is expressed by a lightness difference and a saturation difference. be able to.

  For example, as illustrated in FIG. 6, the change amount calculation unit 106 can be configured by 3DLUTs (three-dimensional look-up tables) 601 to 603 that receive LCh color values. That is, in the 3DLUT, the amount of change in color when a lattice point representing the LCh color space is converted to a color in the color reproduction range of the image output device 103 by the above-described hue preservation conversion method, the hue difference ( Δh, where Δh = 0 in this embodiment, lightness difference (ΔL), and saturation difference (ΔC) are stored for each LCh color space coordinate in the vicinity of the lattice point coordinates and the amount of change. Based on the interpolation calculation based on this, each change amount is calculated.

  Referring to FIG. 1 again, the change amount correction unit 107 calculates the change amount calculation means so that the edge and low frequency components of the change amount (ΔLCh1) output from the change amount calculation unit 106 remain in the image plane. This is a block that corrects and outputs (ΔLCh2) the noticed change amount based on the change amount calculated by the change amount calculating means in the vicinity in a plan view.

  Hereinafter, the correction performed by the change amount correction unit 107 will be described with reference to FIG. FIG. 7A is an example of an image, and there are an area 701 in which the image data after lightness conversion is out of the color gamut that can be output by the image output apparatus 103 and an area 702 in the color gamut. FIG. 7B shows a plot of the saturation of the pixels on the broken line 703 of the image.

  In FIG. 7B, the horizontal axis represents the pixel position, and the vertical axis represents the saturation. A range 705 corresponding to the region 701 with respect to the color gamut 704 that can be output by the image output apparatus 103 schematically illustrated. In FIG. 4, high saturation, that is, out of the color gamut, and ranges 706 and 707 corresponding to the region 702 indicate low saturation, that is, in the color gamut. The color gamut 704 that can be output is the straight line connecting the coordinates in the color space of each pixel and the fixed point on the gray axis described above, or its extension line, and the outermost outline of the color reproduction range of the image output apparatus. Corresponds to the saturation at the intersection with. Further, this saturation is not originally constant for each pixel, but is shown as constant for convenience in FIG. 7B. The change amount (saturation) calculated by the change amount calculation unit 106 corresponds to the arrow 708 in the range corresponding to the region 701, and is 0 in the range corresponding to the region 702.

  FIG. 7C shows a pixel change amount (saturation) 709 on the broken line 703 of the image. In FIG. 7C, the horizontal axis represents the pixel position, and the vertical axis represents the amount of change (saturation).

  The change amount correcting unit 107 corrects the change amount so as to leave an edge and a low frequency component in the image plane of the change amount. Here, leaving the low frequency component means removing the high frequency component when turned over, and can be realized by applying a smoothing filter on the image plane, for example. Further, leaving an edge means leaving edge information. In other words, generally, when a smoothing filter is applied, the edge information is also smoothed and processed in a direction in which the edge information disappears. If there is an edge, for example, the smoothing process is performed only on each side of the edge. By doing so, processing can be performed so as to leave edges and low frequency components. FIG. 7D shows an example. When a smoothing filter is applied in the range corresponding to the region 701 and the range corresponding to the region 702 with the edge as a boundary, the processing as shown in 710 is performed. Indicates that the result is obtained. That is, in the range corresponding to the region 701, the amount of change is smoothed, and the variation of the amount of change is more gradual. On the other hand, in the range corresponding to the region 702, the change amount of the range corresponding to the region 701 is blocked and is not affected, and the change amount remains zero. That is, processing that preserves edges and low frequency components is realized.

  Next, an example of processing performed by the variation correction unit 107 (spatial filter processing is performed on the variation so as to preserve edges and low-frequency components) will be described with reference to FIG. FIG. 8A is a processing flowchart of the change amount correction unit 107. First, the change amount correcting unit 107 initializes the position pointer of the target pixel in the image data (step 801).

  Next, the change amount correcting unit 107 extracts the change amount C of the target pixel (step 802). Next, the variation correction unit 107 initializes the position pointer of the point-symmetric pair (step 803). Here, the change amount correction unit 107 has a predetermined processing range, and the target pixel is set as the center pixel of the range. FIG. 8B shows the position of the pixel of interest 821 in an example in which the predetermined processing range is 7 × 7 pixels. Further, the change amount correcting unit 107 compares the change amount of a pair of pixels (for example, the pixels 822 and 823, the pixels 824 and 825, etc.) at the point target position with the target pixel 821 as the center, and changes the target pixel 821. Choose the one that is close to the amount. Then, a predetermined weighting coefficient as illustrated in FIG. 8C is multiplied (for example, the change amount of the pixels 824 and 825 is multiplied by the coefficient 2 respectively, and the change of the pixel of interest 821 indicated by “X”). The amount C is multiplied by a coefficient 4), and this is totaled over the entire processing range. For example, when the processing range is 7 × 7 pixels as shown in FIG. 8B, the pixel pair at the point target position is (7 × 7-1) ÷ 2 = 24.

  Referring again to FIG. 8A, after initializing the position pointer of the point symmetric pair, the amount of change of the point symmetric pair indicated by the pointer (referred to as A and B, respectively) is acquired (step 804).

  Next, the difference C between the change amount C of the target pixel and the change amounts A and B of the point symmetric pair are compared (step 805), and the one close to the change amount C of the target pixel 821 is weighted and added (change amounts A and C). When the difference is smaller, the change amount A is selected at step 806 and the change amount A is weighted and added. When the difference between the change amounts B and C is smaller, the change amount B is selected and changed at step 807. The amount B is weighted and added). If the difference is equal, the change amounts A and B are compared (step 808), and if they are equal, either (B in FIG. 8A) is weighted and added. On the other hand, if they are not equal, the average of the change amounts A and B, that is, the change amount C is weighted and added (step 809).

  Then, it is determined whether or not all pixel pairs have been processed, and if not processed, the position pointer of the point-symmetric pair is moved to the next, and the processing of steps 804 to 809 is repeated (step 810). Also, if the processing of all pixel pairs has been completed, the weighted average of the amount of change is calculated from the weighted addition result (the weighted addition result of the pixel of interest 821 is divided by the sum of the coefficients of the pixel positions subjected to weighted addition). Then, the corrected change amount is obtained (step 811).

  Then, it is determined whether all the pixels of the image data have been processed as the target pixel. If the target pixel is not processed, the position pointer of the target pixel is moved to the next, and the processes in steps 802 to 811 are repeated (step 812). If the processing of all the pixels of the image data has been completed, the change amount correction processing is terminated.

  According to the above-described processing, for example, when a linear edge of the amount of change exists in the vicinity of the target pixel 821 as shown in FIG. 8D, the amount of change close to the target pixel 821 is aggregated (weighted average of the hatched portion). ), The modified change amount is an efficient preservation of the change amount edge.

  Note that the processing of the variation correction unit 107 of the present invention is not limited to the above-described one. For example, as shown in FIG. 8E, the amount of change of the pixel of interest 821 is compared by comparing the amount of change of pixels in four directions (for example, the pixels 826 to 829) at the point target position with the pixel of interest 821 as the center. It is also possible to select and weight-add the one closest to. In this case, for example, when a right-angled edge of the change amount exists in the vicinity of the target pixel 821 as shown in FIG. 8F, the corrected change amount is an efficiently stored edge of the change amount.

  Further, the description has been given focusing on the processing of the amount of change in saturation, but the description is omitted because the same applies to the lightness and, in some cases, the amount of change in hue.

Referring to FIG. 1 again, the color correction unit 108 corrects the color of the lightness-converted image data (LCh2) output by the lightness conversion unit 105 based on the change amount (ΔLCh2) corrected by the change amount correction unit 107. Thus, the color correction image data (LCh3) is output. Here, each component of variation ^{(ΔLCh2), (ΔL2 *,} ΔC2 *, Δh2 *), the components of the brightness conversion image data ^{(L2 *, C2 *, h2} *), each component of the color corrected image data Is (L3 ^* , C3 ^* , h3 ^* ), the color correction unit 108 performs correction by the following processing, for example.

尚、本実施例では、色相保存変換法を使用しているので、Δｈ２^＊＝０である。

In this embodiment, since the hue preserving conversion method is used, Δh2 ^* = 0.

  FIG. 7E shows the corrected saturation 711 on the broken line 703 in the image of FIG. As shown in FIG. 7E, the corrected saturation 711 moves to the vicinity of the color gamut 704 that can be output by the image output apparatus 103, but does not stick to the outermost contour, and the brightness-converted image data is present. The information on the change in saturation (low frequency component) is retained.

  Referring to FIG. 1 again, the color conversion unit 109 converts the color correction image data (LCh3) output from the color correction unit 108 into the color reproduction range of the image output device 103 described above or a color reproduction range obtained by correcting the color reproduction range. This is a block to convert to color. As a conversion method at that time, for example, the above-described typical conversion methods such as a hue preservation conversion method can be used. In this embodiment, since the color printer is used as the image output device 103, the output image data output from the color conversion unit 109 is cyan (C), magenta (M), yellow used by the color printer. The color material recording signals (CMYK) are (Y) and black (K).

  FIG. 7F shows the saturation 712 of the output image data output from the color conversion unit 109 on the broken line 703 in the image of FIG. As shown in FIG. 7 (f), since it is converted into a color reproduction range of the output device 103 or a color reproduction range obtained by correcting the color reproduction range, it partially sticks to the outermost part, but the brightness converted image data has Since the information on the saturation change (low frequency component) remains, the discriminability of the input image data can be maintained.

  Since the image input device 101 of the image processing system shown in FIG. 1 is a digital still camera, it outputs a photographic image. For this reason, the conversion method when the change amount calculation unit 106 converts to a color within a predetermined color reproduction range and the control of the conversion method of the color conversion unit 109 are not touched. However, the appropriate conversion method differs between graphics such as graphs and charts and photographic images, so when the image input device outputs both, the conversion method depends on the type (graphics and photographic image). Control better.

  FIG. 9 shows a configuration of an image processing system according to the second embodiment. In the following description, the same blocks as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In FIG. 9, reference numeral 901 denotes an image input device which outputs a graphic image such as a photographic image or chart together with its attribute data. For example, this corresponds to the case where a personal computer that executes word processor software outputs an image to a printer. The personal computer outputs image data of a photographic image or converts vector data such as a graph into a bitmap. The image data is converted and output to the color specification conversion unit 104 of the image processing apparatus 902. Also, the image input device 901 outputs attribute data corresponding to the image data to the conversion method setting unit 903. Here, the attribute data is data indicating the type of image data, that is, whether it is a photographic image or a graphics image such as a chart, and the like. The classification according to the image suitable for each of the hue preservation conversion method and the saturation preservation conversion method is shown.

  The conversion method setting unit 903 generates a signal designating a conversion method according to the input attribute data. For example, if the attribute data is a photographic image, the hue preservation conversion method is specified. If the attribute data is a graphics image such as a chart, the saturation preservation conversion method is designated.

  The change amount calculation unit 904 is a block that calculates a color change amount (ΔLCh1) when the color of the image data output from the lightness conversion unit 105 is converted into a color within a predetermined color reproduction range. . Here, the predetermined color reproduction range is, for example, the color reproduction range of the image output device 103 described above or a color reproduction range obtained by correcting the color reproduction range. Further, the conversion method at that time follows the method specified by the conversion method setting unit 903.

  Further, the color correction unit 108 corrects the color of the lightness conversion image data (LCh2) output from the lightness conversion unit 105 based on the change amount (ΔLCh2) corrected by the change amount correction unit 107, thereby correcting the color correction image. This block outputs data (LCh3). According to this, the image output device 103 can output image data after brightness conversion that is out of the color gamut of the image output device 103, in the same manner as the example shown in FIG. 7E, according to the attribute data of the image data. The image data is corrected so as to substantially match the color gamut. At that time, the information (low frequency component) such as the saturation change that the brightness conversion image data has is held without completely sticking to the outermost outline of the color gamut.

  The color conversion unit 109 is a block that converts the color correction image data (LCh3) output from the color correction unit 108 into a color within the color reproduction range of the image output device 103 described above or a color reproduction range obtained by correcting the color reproduction range. is there. As a conversion method at that time, for example, a conversion method according to the attribute data of the image data may be used. However, the color correction unit 108 has already gathered in the vicinity of the color gamut that the image output device 103 can output. Since it has been converted to image data, the conversion method according to the attribute data does not make much sense here. For this reason, in this embodiment, conversion using the hue preservation conversion method is performed regardless of the attribute data.

  As described above, according to the present embodiment, since the optimum change amount is calculated and the image data is corrected according to the attribute information of the input image data, the deterioration of the identification of the image data is further reduced. be able to.

  FIG. 10 shows a configuration of an image processing system according to the third embodiment. In the following description, the same blocks as those in the first and second embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  In FIG. 10, 101 is an image input device, 1001 is an image processing device, and 103 is an image output device. Image data after lightness conversion output from the lightness conversion unit 105 of the image processing device 1001 is sent to a resolution reduction processing unit 1002. Entered.

  The resolution reduction processing unit 1002 is a block that reduces the resolution of image data after lightness conversion to reduce the data amount. For example, the resolution reduction processing unit 1002 performs processing such as thinning out image data after lightness conversion into main and sub 1/4.

  The change amount correcting unit 1003 is a block that corrects the change amount so as to leave an edge and a low frequency component on the image plane of the change amount. Here, since the change amount input to the change amount correction unit 1003 is calculated based on the color of the image data after the brightness conversion converted into the low resolution by the resolution reduction processing unit 1002, the above-described change amount correction is performed. The ratio of the low frequency component is larger than the amount of change input to the unit 107. For this reason, the change amount correction unit 1003 can obtain the same effect even if the processing range is reduced. That is, it is possible to simplify the processing by reducing the number of repetitions of the flowchart shown in FIG.

  The resolution restoration processing unit 1004 is a block that matches the resolution of the amount of change corrected to leave the edges and low-frequency components with the resolution of the image data after brightness conversion. For example, as described above, the image data after brightness conversion is mainly processed. In the case of decimation to sub 1/4, conversion is performed by the nearest neighbor method, bilinear method, bicubic method, etc. to the main sub 4 times.

  Accordingly, the color correction unit 108 can correct the color of the lightness converted image data (LCh2) output from the lightness conversion unit 105 based on the change amount (ΔLCh2) in which the resolutions are matched.

  As described above, according to the present embodiment, since the resolution reduction processing unit 1002 and the resolution restoration processing unit 1004 are included, the processing in the change amount correction unit 1003 can be performed more easily without reducing the degradation of discrimination. It can be realized with a configuration.

  Although the present invention has been described above as an image processing apparatus having processing blocks as shown in FIG. 1 and the like, the object of the present invention may be achieved as an image processing method having the functions of the above-described embodiments. good.

  FIG. 11 is a flowchart of an image processing method having functions equivalent to those of the image processing apparatus shown in FIG.

  First, an image data acquisition process (step 1101) for acquiring AdobeRGB original image data stored in an image input device or the like is performed. In this example, it is assumed that the color scheme of image data is implicitly determined to be AdobeRGB, but processing that determines the color scheme by communicating with an image input device or the like is added in advance. Also good.

  Next, a color conversion process (step 1102) is performed to convert the input image data into a color system that is handled internally. In the colorimetric conversion process (step 1102), for example, the above-described equations (1) to (6) are converted, and converted to LCh1 or the like which is a cylindrical coordinate system of CIELAB colorimetric values.

  Next, in the lightness conversion process (step 1103), the lightness of the original image data is within the lightness range of the image output device based on the lightness region in which the original image data can be expressed and the lightness region that can be output by the image output device 103 or the like. The process of converting and outputting. Here, the brightness range that can represent the original image data is determined by the above-described color specification format. The brightness range that can be output by the image output apparatus is determined by the color gamut that can be output by the image output apparatus 103, and is acquired in advance by communicating with the image output apparatus 103, for example.

  Next, in the change amount calculation process (step 1104), the color change amount (ΔLCh1) when the color of the image data converted in the lightness conversion process (step 1103) is converted into a color within a predetermined color reproduction range. ) Is calculated. Here, the predetermined color reproduction range is, for example, the color reproduction range of the image output device 103 described above or a color reproduction range obtained by correcting the color reproduction range. Further, as the conversion method at that time, for example, the above-described typical conversion method can be used. In the following, a case where the hue preservation conversion method is used will be described as an example, but the present invention is not limited to this.

  Next, in the change amount correction process (step 1105), the change amount calculation unit is configured to leave an edge and a low frequency component in the image plane of the change amount (ΔLCh1) calculated in the change amount calculation process (step 1104). The calculated amount of change is corrected based on the amount of change calculated by the change amount calculating means in the vicinity of the plane and output (ΔLCh2).

  Next, in the color correction process (step 1106), the lightness converted image data (LCh2) converted by the lightness conversion process (step 1103) based on the change amount (ΔLCh2) corrected by the change amount correction process (step 1105). The color correction image data (LCh3) is output. Here, for example, the processing shown in the equation (7) is performed.

  Next, in the color conversion process (step 1107), the color correction image data (LCh3) corrected by the color correction process (step 1106) is used as the color reproduction range of the image output device 103 or the like described above or the color reproduction obtained by correcting the color reproduction range. Convert to a range of colors. As a conversion method at that time, for example, the above-described typical conversion methods such as a hue preservation conversion method can be used. In this embodiment, since the color printer is used as the image output device 103, the output image data output by the color conversion processing 1107 is cyan (C), magenta (M), yellow used by the color printer. The color material recording signals (CMYK) are (Y) and black (K).

  Finally, an image data transmission process (step 1108) is performed in which the image data converted in the color conversion process (step 1107) is transmitted to the image output device 103 or the like.

  As described above, since the present embodiment includes processing steps having the same functions as the blocks included in the image processing apparatus in FIG. 1, the input image data is converted into an image within the color reproduction range of the image output apparatus. When converting to data, it was possible to reduce the deterioration of the discriminability of the input image data while having a high-precision and simple configuration.

  Note that an image processing method having functions equivalent to those of the image processing apparatus shown in FIGS.

  Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and a computer (CPU or MPU) of the system or apparatus uses the storage medium as a storage medium. It can also be achieved by reading and executing the stored program code. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments. As a storage medium for supplying the program code, for example, a hard disk, an optical disk, a magneto-optical disk, a nonvolatile memory card, a ROM, or the like can be used. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) operating on the computer based on an instruction of the program code. A case where part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing is also included. Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. This includes the case where the CPU or the like provided in the board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing. When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowcharts described above. Further, the program for realizing the functions and the like of the embodiments of the present invention may be provided from a server by communication via a network.

DESCRIPTION OF SYMBOLS 101 Image input device 102 Image processing apparatus 103 Image output device 104 Color conversion part 105 Lightness conversion part 106 Change amount calculation part 107 Change amount correction part 108 Color correction part 109 Color conversion part

JP 2001-169136 A Japanese Patent No. 3865696

“Efficient hue-preserving and edge-preserving spatial color gamut mapping (15th Color Imaging Conference)”

Claims (7)

  An image processing device that performs processing for converting input image data into image data within a color reproduction range of an image output device, wherein the color of the input image data is within a first color reproduction range. Change amount calculating means for calculating a change amount of color when converted into color, and the change amount calculating means so as to leave at least an edge and a low frequency component in the image plane of the change amount calculated by the change amount calculating means; The change amount correcting unit that corrects the calculated change amount based on the change amount in the vicinity in a plane, and the color of the input image data based on the change amount corrected by the change amount correcting unit. An image processing apparatus comprising: color correcting means for correcting; and color converting means for converting the color of the image data corrected by the color correcting means into a color within a second color reproduction range.   It has attribute information setting means for setting attribute information of the input image data, and the change amount calculating means calculates a color change amount based on the attribute set by the attribute information setting means. The image processing apparatus according to claim 1.   2. The change amount calculation unit calculates a color change amount when the color of the input image data is held and converted to a color within a first color reproduction range. Or the image processing apparatus of 2.   Low resolution conversion means for reducing the resolution of the image data; and resolution restoration means for restoring the resolution of the image data corresponding to the low resolution conversion means; and the change amount calculation means is the low resolution conversion means A color change amount is calculated when the color of the input image data processed by the above is converted into a color within the first color reproduction range, and the color correction unit is processed by the resolution restoration unit. 4. The image processing apparatus according to claim 1, wherein a color of the input image data is corrected based on a change amount corrected by the change amount correction unit. 5.   An image processing method for performing processing for converting input image data into image data within a color reproduction range of an image output device, wherein the color of the input image data is within a first color reproduction range. A change amount calculating step of calculating a change amount of the color when converted into color, and the change amount calculating step so as to leave at least an edge and a low frequency component in the image plane of the change amount calculated by the change amount calculating step; The change amount correction step of correcting the calculated change amount of interest based on the change amount in the vicinity in a plane, and the color of the input image data based on the change amount corrected by the change amount correction step An image processing method comprising: a color correction step for correcting; and a color conversion step for converting the color of the image data corrected by the color correction step into a color within a second color reproduction range.   A program for causing a computer to realize the image processing method according to claim 5.   A computer-readable recording medium on which a program for causing a computer to implement the image processing method according to claim 5 is recorded.

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