JP4803122B2 - Color processing apparatus and program - Google Patents

Description

  The present invention relates to a color processing apparatus and program, and in particular, sets a color gamut conversion condition so that the color gamut of image data in a predetermined color space that does not depend on a specific apparatus is within the output color gamut, and sets the color The present invention relates to a color processing apparatus including color gamut conversion means for performing color gamut conversion of input image data according to a gamut conversion condition, and a color processing program for causing a computer to function as the color processing apparatus.

  The color gamut that can be reproduced by image output devices such as color printers and displays, and the color gamut that can be captured by image input devices such as scanners differ depending on the type and model of the device, and are displayed on the display, for example. When printing an image with a color printer, if the image data used to display the image on the display is output to the color printer as it is, it is reproduced on both devices due to differences in color gamut between the two devices. The colors of the resulting images are significantly different. As a technique for improving the difference in color reproduction, the color of image data to be output is a device-independent color space that does not depend on a specific device (device) (for example, CIE (Commission Internationale de l'Eclairage)). CAM colors defined by the uniform perceptual color space such as the L * a * b * color space recommended by, the color space of the tristimulus XYZ color system, and the color appearance model such as CIECAM02 (Color Appearance Model 2002) In the past, it has been proposed to perform color gamut conversion (also referred to as gamut mapping) for replacement with a color within the color gamut of the image data output target device.

The conversion conditions in the color gamut conversion are set by, for example, applying a predetermined conversion rule (also referred to as a mapping rule) and converting the input color value to the output color gamut (the color reproduction gamut in the device-independent color space of the device on the output side) ) Is converted to an arbitrary color value (output color value) and the correspondence between the two is the individual color located in the input color gamut (color reproduction gamut in the device-independent color space of the device on the input side) This can be realized by performing each value as an input color value. In addition, for the purpose of improving the image quality of an image output through color gamut conversion, it is also proposed to perform color gamut conversion by adding an arbitrary restriction condition. In order to prevent color turbidity in color printing, for the color data of yellow, magenta, and cyan only in the color space of the conversion source, the color is the color in the converted color space corresponding to the printing ink. A technique for converting color data by shifting the hue so as to reduce the mixing of different color components is disclosed.
Japanese Patent No. 3794084

  However, when arbitrary restrictions are added to the color gamut conversion, in addition to the original purpose of the color gamut conversion, which is to put the color gamut of the image data after the color gamut conversion into the output color gamut, It is necessary to set the gamut conversion conditions so that they are satisfied at the same time, but the algorithm for setting the gamut conversion conditions is more complicated than the original, and try to set the gamut conversion conditions so that the added constraints are also satisfied at the same time. Then, the algorithm became very complicated, and in the end it was the actual situation that the algorithm was developed by repeating trial and error. Further, each time a new constraint condition appears, it is necessary to newly develop an algorithm for setting a color gamut conversion condition that satisfies the new constraint condition at the same time.

  The present invention has been made in consideration of the above facts, and an object of the present invention is to obtain a color processing apparatus and a color processing program that can easily realize color gamut conversion that satisfies a set constraint condition.

  The restriction condition added to the color gamut conversion itself is simple, such as affine transformation, for example, when it is desired to convert the first specific color in the input color gamut to the second specific color in the output color gamut, etc. In most cases, the color conversion can be realized by simple processing. However, if this is performed simultaneously with the color gamut conversion, the algorithm for setting the color gamut conversion condition becomes very complicated. The inventor of the present application has made the present invention paying attention to the fact that the constraint condition itself added to the color gamut conversion can be realized by a simple process.

  Based on the above, the color processing device according to the first aspect of the present invention is based on output color gamut information representing an output color gamut on a predetermined color space that does not depend on a specific device, and an image on the predetermined color space. A color gamut that sets the color gamut conversion condition for converting the image data according to a predetermined conversion rule so that the data color gamut falls within the output color gamut, and performs the color gamut conversion of the input image data according to the set color gamut conversion condition. A color value of a predetermined color in the input image data through the setting unit by the conversion unit, a setting unit for setting a constraint condition for the color gamut conversion, and a color gamut conversion by the color gamut conversion unit; The color value of the predetermined color is changed so as to be converted into an output-corresponding color satisfying the set constraint condition, and a color value other than the color value of the predetermined color in the input image data is changed. Color before changing the predetermined color Is configured to include a preprocessing means, the performing pre-processing is changed according to the relationship between the color value after changed.

  According to the first aspect of the present invention, the color gamut of the image data on the predetermined color space is within the output color gamut based on the output color gamut information representing the output color gamut on the predetermined color space that does not depend on a specific device. Color gamut conversion means for setting a color gamut conversion condition for converting image data according to a predetermined conversion rule and performing color gamut conversion for input image data according to the set color gamut conversion condition is provided. The predetermined color space is preferably the CAM color space defined by the color appearance models CIECAM02 and CIECAM97s, but other color spaces such as the CIE L * a * b * color space and the CIEXYZ color space are applied. Also good. Further, as the predetermined conversion rule (mapping rule), any of various known conversion rules such as a conversion rule using a reference anchor may be used.

  According to the first aspect of the present invention, there is provided setting means for setting a constraint condition for the color gamut conversion. The preprocessing means according to the first aspect of the invention provides the color gamut conversion by the color gamut conversion means. To change the color value of the predetermined color so that the color value of the predetermined color in the input image data is converted into an output-corresponding color that satisfies the constraint condition set via the setting unit, and Pre-processing is performed to change color values other than the color value of the predetermined color in the image data in accordance with the relationship between the color value before the change of the predetermined color and the color value after the change. In addition, as the predetermined color, for example, as described in claim 3, the color space of the input image data before being converted into the image data of the predetermined color space, or the specific device to which the image data is output A reference color that defines a dependent color space and its complementary color (any color can be set as this reference color and its complementary color, for example, it may be a reproduction color of R, G, B, C, M, Y) In addition, it may be a color located in the vicinity of an arbitrary color space, or other reproduction colors having the same hue and different brightness and saturation as R, G, B, C, M, and Y. A saturated color of at least one of them may be applied, but other colors may be applied. The saturated color is a primary color of a color material such as ink or a primary color and a secondary color of a color stimulus such as a monitor, and is a reproduction color of RGBCMY.

  In the preprocessing by the preprocessing unit, the color value of a predetermined color in the input image data is converted into an output-corresponding color satisfying the constraint condition set via the setting unit by color gamut conversion by the color gamut conversion unit. As described above, since the color value of the predetermined color is changed, the color value of the predetermined color in the input image data is an output satisfying the constraint condition in accordance with the color gamut conversion by the color gamut conversion means. Converted to the corresponding color. In the preprocessing by the preprocessing means, the color values other than the color value of the predetermined color in the input image data are changed according to the relationship between the color value before the change of the predetermined color and the color value after the change. Therefore, with respect to color values other than the color value of the predetermined color in the input image data, there is a gap between the color value of the predetermined color in the predetermined color space in accordance with the color gamut conversion by the color gamut conversion means. Thus, the color value is converted into an appropriate color value. For the original purpose of color gamut conversion, the color gamut conversion by the color gamut conversion means is performed after the preprocessing described above, so that the color gamut of the image data after the color gamut conversion is included in the output color gamut. In addition, image data that satisfies the set constraint conditions at the same time can be obtained.

  Thus, according to the first aspect of the present invention, the color gamut conversion processing in which the constraint condition is set includes the pre-processing for changing the color value so as to satisfy the set constraint condition, and the image data after the color gamut conversion. Since the color gamut is separated into the original processing (color gamut conversion by the color gamut conversion means according to the present invention) for accommodating the color gamut in the output color gamut, the color gamut can be used even when a new constraint condition appears. Without changing the content of the processing by the conversion means (algorithm that functions as the color gamut conversion means), it is possible to cope by changing only the content of the processing by the preprocessing means (the algorithm that functions as the preprocessing means) Further, since the preprocessing itself by the preprocessing means is a simple process, the contents of the processing by the preprocessing means (algorithm that functions as the preprocessing means) can be easily performed. Therefore, according to the first aspect of the present invention, it is possible to easily realize color gamut conversion that satisfies the set constraint conditions.

  The invention described in claim 1 is not limited to the color gamut conversion unit performing the color gamut conversion after the preprocessing unit performs the preprocessing. For example, as described in claim 2, the preprocessing The means pre-processes each color value in the input color gamut corresponding to the color reproduction gamut of the input image data in a predetermined color space, and the color gamut conversion means has undergone pre-processing by the pre-processing means. Color gamut conversion conditions are set based on individual color values, and pre-processing conditions for associating the values before and after the change of individual color values in the pre-processing by the pre-processing means and the color gamut conversion means are set. And an integrated conversion condition obtained by integrating the color gamut conversion conditions, and by converting individual color values of the input image data according to the generated integrated conversion condition, pre-processing by the pre-processing means for the input image data Simultaneous gamut conversion by gamut conversion means It is also possible to configure to be performed.

  According to the first aspect of the present invention, the color corresponding to the output corresponding to the color value of the predetermined color in the input image data satisfying the constraint condition set via the setting means by the color gamut conversion by the color gamut conversion means. Specifically, the change of the color value of the predetermined color by the preprocessing means so as to be converted is, specifically, a constraint condition set from the color value of the predetermined color as described in claim 4, for example. Inverse conversion of conversion based on a predetermined conversion rule (conversion rule that the gamut conversion means applies to setting the gamut conversion condition) for the color value of the output-corresponding output color that is satisfactory This is realized by obtaining the color value of the input corresponding color by replacing the color value of the predetermined color with the color value of the input corresponding color.

  Further, in the invention described in claim 4, the constraint condition set via the setting means includes a constraint condition that places importance on input color reproduction, and the input color reproduction is emphasized via the setting means. When the constraint condition is set, the pre-processing means, for example, as described in claim 5, the color value of the predetermined color as the color value of the output corresponding color satisfying the constraint condition on the outline of the output color gamut. The first color value having the smallest distance in the predetermined color space, or the reference color having the same hue and the same lightness as the color value of the predetermined color on the outline of the output color gamut A distance from a value within a predetermined color space within a threshold value, on the outline of the output color gamut and on the second color value of the same color as the color value of the predetermined color, or on the outline of the output color gamut and Evaluate a color value of a predetermined color and a vector distance on a predetermined color space (for example, a color difference or a distance on a predetermined color space) A third color value having a minimum predetermined evaluation function or the like, or a color value within a triangular color range on a predetermined color space having the first to third color values as vertices. It is preferable to configure.

  The first color value and the second color value are both the same hue as the color value of the predetermined color, the difference in brightness and saturation is small, and the color located on the outline of the output color gamut Since the first color value or the second color value is the color value of the output-corresponding color, the color value of the predetermined color is changed to the first color value or the second color value along with the color gamut conversion. Therefore, the color gamut conversion satisfying the constraint condition that emphasizes the color reproduction of the input can be realized. Further, the third color value is the color value of the predetermined color because the color distance between the color value of the predetermined color and the vector distance on the predetermined color space is the smallest on the outline of the output color gamut. However, according to an experiment conducted by the present inventor, even if the color value of a predetermined color is converted to the third color value, depending on the predetermined color, the input color reproduction Is converted to a color value that is evaluated as being intact, and even when the third color value is obtained as the color value of the output-corresponding color that satisfies the constraints, the input color reproduction Color gamut conversion that satisfies the constraints that place emphasis on can be realized.

  The color values in the triangular color range on the predetermined color space with the first to third color values as vertices are, for example, on the predetermined color space among the first to third color values. Using a value on a line connecting any two color values (for example, the first and second color values) (for example, a color value corresponding to the average of the two color values) or the first to third color values. Examples include color values located at arbitrary positions within the obtained triangular color range (for example, color values corresponding to the average of the first to third color values). For example, even when a color value of a predetermined color is converted into a color value within the triangular color range, depending on the predetermined color, it is converted into a color value that is evaluated as having an intact color reproduction. Even when the color value within the triangular color range is obtained as the color value of the output corresponding color that satisfies the constraint conditions, It is possible to realize a color gamut conversion constraint also satisfies to emphasize.

Also, suitable color value as an output corresponding color of the color values that satisfy the constraints, also differ by a predetermined color to convert (mostly predetermined color hue). In view of this, in the invention of claim 5 Symbol mounting, for example as described in claim 6, the pre-processing means, a plurality of kinds of color values as the color value of the output corresponding color satisfying the constraint condition (first to any or use of the third color values and color values in the triangular color range), it is preferably configured to switch a predetermined color. As a result, it is possible to optimize the color value of the output-corresponding color that satisfies the constraint conditions in accordance with the predetermined color (hue, etc.) to be converted.

As one aspect of claim 6 , for example, as described in claim 7 , the preprocessing unit has a hue within a range in which the predetermined color is b * <0 in the CIEL * a * b * color space. In this case, the third color value can be used as the color value of the output corresponding color that satisfies the constraint condition. According to an experiment conducted by the inventor of the present application, when the predetermined color is a hue within the above range, it is confirmed that the third color value is suitable as the color value of the output corresponding color that satisfies the constraint condition. When the predetermined color is a hue within the above range, the third color value is used as the color value of the output-corresponding color that satisfies the constraint condition. Color gamut conversion satisfying with higher accuracy can be realized.

In the invention described in claim 1, for example, as described in claim 8 , at least the lightness of the color value of the input image data is output for the input image data whose color value is changed by the preprocessing means. It is preferable that a range adjustment process for adjusting according to the color gamut or the image output condition is performed in advance. As the range adjustment processing for adjusting the color value of the input image data according to the output color gamut, for example, the maximum value and the minimum value of the lightness in the input image data match the maximum value and the minimum value of the lightness in the output color gamut. Includes a process for adjusting the color value of the input image data, and the range adjustment process for adjusting the color value of the input image data according to the image output condition is performed, for example, through pre-processing and color gamut conversion according to the present invention. When the output image data is used for recording an image on a predetermined recording sheet, the color value of the input image data is adjusted so that white in the input image data matches the color (background color) of the predetermined recording sheet. Processing and the like.

When the color value of the predetermined color is converted to the third color value according to claim 5, the color value is converted so that the color value moves in a direction intersecting the hue plane in the predetermined color space. However, performing the above range adjustment processing on the input image data is particularly effective when the color value is converted in a direction in which the color value of a predetermined color intersects the hue plane. Yes, more appropriate color gamut conversion can be realized.

In the first aspect of the present invention, the pre-processing means, for example, as described in the ninth aspect , of the color values other than the color value of the predetermined color, the color value to be changed in hue equal to the predetermined color. Reduced the vector distance between the color value before the change of the predetermined color and the color value after the change in accordance with the saturation ratio between the color value before the change of the predetermined color and the color value to be changed. Obtain the vector distance, change the color value of the change target based on the calculated vector distance, and for the color value of the change target for which the predetermined color of the same hue does not exist, the color value and the hue of the change target are approximate The vector distance between the color value before the change of the first predetermined color and the color value after the change is set to the saturation ratio between the color value before the change of the first predetermined color and the color value to be changed. The first vector distance reduced correspondingly is obtained, and the color value to be changed is similar to the hue of the second predetermined color before the change. A second vector distance obtained by subtracting the vector distance between the value and the color value after the change according to the saturation ratio between the color value before the change of the second predetermined color and the color value to be changed; The first vector distance and the second vector corresponding to the hue difference between the color value to be changed and the color value before the change of the first predetermined color and the color value before the change of the second predetermined color It is preferable that the weighted average value of the distance is calculated and the color value to be changed is changed based on the vector distance corresponding to the calculated weighted average value.

  As a result, among the color values other than the color value of the predetermined color, the color value having the same hue as the predetermined color is changed according to the relationship between the color value before the change of the predetermined color and the color value after the change. For a color value for which a predetermined color having the same hue does not exist, the relationship between the color value before the change of the first predetermined color and the color value after the change that is similar to the color value, and Since the color value is changed according to the relationship between the color value before the change and the color value after the change of the second predetermined color whose hue approximates, the color value other than the color value of the predetermined color Regardless of whether or not a predetermined color having the same hue exists, a gap or the like between the color value of the predetermined color in the predetermined color space is obtained along with the color gamut conversion by the color gamut conversion means. It can be changed so as to be converted into an appropriate color value that does not occur.

Further, in the invention of claim 9, if the constraints that emphasize color reproduction output via the setting means is set, pre-processing means, for example as described in claim 1 0, a predetermined color Of the color values other than the color value, it is preferable that the color value is changed by changing only a color value outside the output color gamut in a predetermined color space. As a result, the color gamut conversion is not performed on the color values in the output color gamut in the predetermined color space among the color values other than the color values of the predetermined color without performing preprocessing (color value change) by the preprocessing means. Since only the color gamut conversion is performed by the means, the color gamut conversion can be performed so that the output color reproduction is more important.

Further, in the invention according to the first aspect, for example as described in claim 1 1, the pre-processing means, of the predetermined color, a color which color values is within the output color gamut on a predetermined color space Is preferably excluded from the color value change target. When the reference color that defines the color space depending on the specific device to which the image data is output and the saturated color of its complementary color are used as the predetermined color, the color value of the predetermined color in the input image data is the predetermined color space. Although the probability of being within the output color gamut above is not high, as described above, among the predetermined colors, the color value within the output color gamut within the predetermined color space is changed. When a color whose color value falls within the output color gamut in a predetermined color space appears as a predetermined color by excluding it from the target, color reproduction in this color and the surrounding color area is input image The data can be matched with high accuracy.

Color processing program according to the invention of claim 1 wherein the computer based on the output color gamut information representing the output color gamut on a predetermined color space independent of the particular device, on the predetermined color space A color for which the color gamut conversion condition for converting the image data is set according to a predetermined conversion rule so that the color gamut of the image data is within the output color gamut and the color gamut conversion for the input image data is performed according to the set color gamut conversion condition. A gamut conversion unit, a setting unit for setting a constraint condition for the gamut conversion, and a color value of a predetermined color in the input image data by the gamut conversion by the gamut conversion unit The color value of the predetermined color is changed so as to be converted into an output-corresponding color that satisfies the constraint condition set via the color, and a color value other than the color value of the predetermined color in the input image data The predetermined It is made to function as preprocessing means for performing preprocessing for changing according to the relationship between the color value before the color change and the color value after the change.

Color processing program according to the invention of claim 1 wherein the computer, said color gamut conversion means, since it is a program to function as a setting unit and pre-processing means, the invention of the computer according to claim 1 wherein By executing such a color processing program, the computer functions as the color processing apparatus according to claim 1, and, similarly to the invention according to claim 1, color gamut conversion that satisfies the set constraints is also performed. It can be easily realized.

  As described above, the present invention sets the color gamut conversion conditions so that the color gamut of the image data in the predetermined color space that does not depend on a specific device falls within the output color gamut, and the color gamut conversion of the input image data. In addition to the color gamut conversion means for performing the color gamut conversion by the color gamut conversion means, an output corresponding color in which the color value of a predetermined color in the input image data satisfies the constraint condition set via the setting means The color value of the predetermined color is changed so that it is converted into the color value of the input image data other than the color value of the predetermined color, and the color value before the change of the predetermined color and the color value after the change Since the preprocessing means for performing the preprocessing to be changed according to the relationship is provided, it is possible to easily realize the color gamut conversion that satisfies the set constraint conditions.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic configuration of a computer system 10 according to the present embodiment. The computer system 10 includes a network 12 including a LAN, a plurality of client terminals 14 including PCs (Personal Computers) and the like, and an input device 16 that inputs images (data) to the computer system 10. The output devices 18 for visualizing the image data input from the computer system 10 as images are connected to each other. The input device 16 is, for example, a scanner that reads a document and outputs image data. The output device 18 is, for example, an image forming apparatus (printer or printer) that prints an image represented by input image data on a sheet. And a multifunction machine to which a function as a copying machine or a facsimile machine is added). The network 12 may also be connected to a computer network such as the Internet.

  Each client terminal 14 connected to the network 12 includes a CPU 14A, a memory 14B including a RAM, an HDD (Hard Disk Drive) 14C, and a network interface (I / F) unit 14D. It is connected to the network 12 via the F unit 14D. The client terminal 14 is connected with a display device 20 as one of output devices, a keyboard 22 and a mouse 24 as input means. Note that the input device 16 such as a scanner and the other output device 18 such as an image forming apparatus may be directly connected to the client terminal 14 as in the display device 20. For example, the input device 16 may be a digital still camera or the like in addition to the scanner, but the digital still camera or the like is directly connected to the client terminal 14.

  Further, the HDD 14C of the client terminal 14 performs an OS (Operating System) program, various application programs that operate on the OS and use the input device 16 and the output device 18, and color conversion processing described below on the client terminal 14. A color conversion program to be executed is installed in advance, and a color conversion condition DB (database) capable of registering color conversion conditions such as a profile used in color conversion processing, a color prediction model, and base data are also stored. .

  Next, the operation of this embodiment will be described. In the client terminal 14 according to the present embodiment, image data input from a certain input device 16 or image data used for outputting an image in a certain output device 18 is converted into an image data in another device (output device 18). When used for output, color conversion processing is performed to correct the difference in color appearance of images reproduced or captured by different devices (see FIG. 2). In FIG. 2, the input device 16 that has input image data or the output device 18 that has output an image first is referred to as a “first device”, and the output device 18 that outputs an image later (an output device 18 that is an image data output target). ) Is indicated as “second device”.

  As shown in FIG. 2, the color conversion processing according to the present embodiment is configured by processing of first color conversion, second color conversion, color gamut conversion, third color conversion, and fourth color conversion. Image data input from the first device to the client terminal 14 or used for outputting an image in the first device is a color space (first device) in which the color of each pixel of the image data depends on the first device. Dependent color space: For example, if the first device is a scanner, digital still camera, display device 20 or the like, it is image data represented by color values on the RGB color space), and color conversion according to this embodiment is performed on the image data In the processing, the first color for converting the color value on the first device-dependent color space into the color value on the color value on the color space (first device-independent color space) independent of a specific device (apparatus). Perform conversion. In the following description, the L * a * b * color space, the XYZ color space, and the like are suitable as the first device-independent color space.

  Next, with respect to the image data that has undergone the first color conversion, the color value in the first device-independent color space is changed to a color space suitable for the color gamut conversion without depending on a specific device (apparatus). A second color conversion is performed for conversion to a color value on the device-independent color space. Note that the second device-independent color space is preferably a color space that represents the appearance of a color excluding the influence of viewing conditions. For example, a color space JCh defined by CIECAM02, which is a color appearance model, or a color A color space Jab obtained from the space JCh is more preferable. Note that the color attribute values a and b of the color space Jab correspond to ac and bc generated from the color attribute values C and h of the color space JCh, and have characteristics that can be converted into hue and saturation. . Further, instead of the color appearance model CIECAM02, the color appearance model CIECAM97s, and the CAM02-US (Uniform color spaces based CIECAM02 color appearance model (p.320-330), M. Ronnier Luo, Guihua Cui, Changiun Li, 2006) may also be used. The second device-independent color space corresponds to the predetermined color space according to the present invention.

  Subsequently, with respect to the image data that has undergone the second color conversion, the difference between the appearance of the image on the first device and the appearance of the image on the second device (the difference in appearance is the difference in the color gamut between the first device and the second device). Color gamut conversion (also referred to as gamut mapping) is performed. Details of the color gamut conversion according to this embodiment will be described later.

  Next, for the image data that has undergone color gamut conversion, the color value in the second device-independent color space is changed to another color space (third device-independent color space: independent of a specific device). For example, the third color conversion is performed for conversion into color values on the L * a * b * color space. Then, for the image data that has undergone the third color conversion, the color value in the third device-independent color space is changed to a color space that depends on the second device (second device-dependent color space: for example, the second device is the display device 20. If the second device is an image forming apparatus, the fourth color conversion is performed. The image data obtained by the color conversion processing composed of each of the above-described processes is output to the second device and used for the output of the image in the second device, so that the color appearance of the image output by the second device is the first. Can match with device.

  The color conversion program installed in the HDD 14C of the client terminal 14 includes a program for performing each process constituting the above-described color conversion process (a first color conversion program for performing the first color conversion, a second color conversion program, Second color conversion program for performing color conversion, color gamut conversion program for performing color gamut conversion, third color conversion program for performing third color conversion, and fourth for performing fourth color conversion Color conversion program) is added, and the above color conversion processing includes the first color conversion program, the second color conversion program, the color gamut conversion program, the third color conversion program, and the third color conversion program added to the color conversion program. This is accomplished by calling up the four-color conversion program in order and causing each process to be performed in order. 1 shows the color conversion program separately from the OS program, the color conversion program may be included in the OS program as an OS standard program. The color gamut conversion program among the above programs corresponds to the color processing program according to the present invention.

  Among the color conversion processes described above, the color conversion is formulated for the second color conversion and the third color conversion, and the color conversion is performed by simply substituting the input color value into the color conversion formula and calculating the output color value. However, for the first color conversion, the fourth color conversion, and the color gamut conversion, it is necessary to perform conversion by generating conversion conditions as necessary. Hereinafter, details of the first color conversion and the fourth color conversion will be described first.

  In the first color conversion and the fourth color conversion, conversion data (profile) for converting an input color value into an output color value is set in a CLUT (color look-up table), and the image data to be converted (for each pixel) is stored in the CLUT. Image data representing colors by input color values) is sequentially input. In order to convert color values with higher accuracy, for example, a one-dimensional lookup table with a gradation table and a gamma curve added may be added to pre-processing and post-processing different from CLUT. Further, a CLUT may be created including the information. Here, as a method of generating a profile, as shown in (1) of FIG. 3, a patch (color chart) of each color with one of the input color value and the output color value known is generated (for example, as a second device). When generating a profile for the fourth color conversion when outputting image data to the image forming apparatus, the color chart is generated by printing a color chart with a known output color value by a printer. When generating the profile for the fourth color conversion when outputting the image data to the display, the color chart is generated by displaying a color chart with a known output color value on the display) For each color chart, the unknown color value of the input color value and the output color value is measured by a colorimeter or the like to obtain data for associating the input color value with the output color value for each color chart. Data How to use as a profile is known.

  However, in the above generation method, it is necessary to form an enormous number of color charts (the same number as the number of grid points of the CLUT) and to measure input color values or output color values for an enormous number of color charts. There is a problem that it takes a lot of labor to generate. For this reason, a method using a color prediction model is also used as another method for generating a profile. The color prediction model is based on base data representing the correspondence between a smaller number of input color values and output color values, and when input color values whose corresponding output color values are unknown are input, This is a program for estimating and outputting a corresponding output color value by various algorithms. Profile generation using the color prediction model generates fewer color charts (color charts with known input color values or output color values) than when generating profiles directly from color charts ((1) in FIG. 3). 3), by measuring an unknown color value of the input color value and the output color value for each generated color chart, base data for associating the input color value and the output color value of each color chart is generated (FIG. 3). (See also (2)). Next, this base data is set in the color prediction model (see also (4) in FIG. 3), each input color value is input to the color prediction model in turn, and output color values output in order from the color prediction model are input. A profile is generated by associating with the input color value (see (5) in FIG. 3). Then, by setting the generated profile in the CLUT (see also (6) in FIG. 3), it is possible to perform color conversion (first color conversion or fourth color conversion) with the CLUT.

  Profile generation using the color prediction model can greatly reduce the number of color charts required compared to generating profiles directly from color charts, which can greatly reduce the effort of profile generation. . In the present embodiment, as a method for generating the conversion conditions (profiles) for the first color conversion and the fourth color conversion, any of the two types of generation methods described above may be used. It is desirable to use a generation method that uses a prediction model.

  Next, the color gamut conversion processing according to the present embodiment will be described with reference to FIG. This color gamut conversion process is realized by the CPU 14A of the client terminal 14 executing a color gamut conversion program.

  In step 50, points (points on the outline surface) constituting the color gamut outline (color reproduction area outline) of the second device on the second device-dependent color space are extracted as outline point groups. As an example, FIG. 5 shows an example of the color gamut outline of the image forming apparatus in a color space (CMYK color space) depending on the image forming apparatus when the second device is an image forming apparatus. 5A shows the upper part of the color gamut outline in the CMYK color space, and FIG. 5B shows the lower part. The entire color gamut outline of the image forming apparatus in the CMYK color space is shown in FIG. It becomes a 12-sided polyhedron combining the solids shown in 5 (A) and (B). In step 50, a point at an arbitrary position on the color gamut outline surface of the second device can be extracted as an outline point group. However, at least a point corresponding to each vertex of the color gamut outline and the color gamut outline can be extracted. It is desirable to extract points corresponding to the sides connecting the vertices as outline points. Further, the interval between the outline points extracted from the side or from the top or the surface other than the side may be constant or non-uniform.

  In step 52, the color values of the outline point group extracted in step 50 (the outline point group representing the color gamut outline of the second device on the second device-dependent color space) are first calculated on the third device-independent color space. (The inverse of the fourth color conversion (FIG. 2) is performed), and further converted to a color value on the second device-independent color space (third color conversion (FIG. 2)) By performing inverse conversion), an outline point group representing the outline of the color gamut (output color gamut) of the second device on the second device-independent color space is obtained. An example of the color gamut outline (the color gamut outline of the second device on the second device-independent color space) constituted by the outline point group that has undergone the conversion in step 52 is shown in FIG. In FIG. 6, the vertices of the color gamut outline are denoted by the same reference numerals as the corresponding vertices among the vertices of the color gamut outline shown in FIG. By the above process, it is possible to obtain outline point groups that constitute the color gamut outline of the second device on the second device-independent color space.

  In the next step 54, the outline point group obtained by the conversion in step 52 is connected as vertices, an outline surface is generated by interpolation or the like, and is converted into a polygon (polyhedral), whereby the second device-independent color space. Output color gamut outline information representing the above-described color gamut outline of the second device as a polyhedron is generated. Thus, based on the generated output color gamut contour information, for example, the color gamut contour of the second device in the second device-independent color space is evaluated and quantified, or the second device is visualized using a general-purpose visualization tool. Various color gamut contours of the second device on the second device-independent color space, such as three-dimensional visualization of the color gamut contour of the second device on the second device-independent color space. It can also be easily used for applications.

  When generating the output color gamut outline information in step 54, for example, out of the outline point group obtained by the conversion in step 52, outline points suitable for the intended use are selectively extracted, and the extracted part The output color gamut outline information may be generated by connecting the outline points only to each other and generating an outline surface by interpolation or the like. Further, the output color gamut outline information may be generated in advance and stored in the HDD 14C, and the output color gamut outline information may be acquired by simply reading the output color gamut outline information. The above output color gamut outline information corresponds to the output color gamut information according to the present invention.

  In the next step 56, input color gamut outline information representing the color gamut outline (input color gamut outline) of the first device (see FIG. 2) on the second device-independent color space is acquired. The input color gamut outline information is extracted, for example, from the outline point group constituting the color gamut outline of the first device on the first device-dependent color space in the same manner as in Steps 50 to 54 described above. By converting the color value of the first color into a color value in the second device-independent color space, an outline point group representing the color gamut outline of the first device in the second device-independent color space is obtained and obtained. The outer contour points are connected as vertices, the outer surface is generated by interpolation or the like, and is polygonized (polyhedral). Alternatively, the input color gamut outline information may be generated in advance and stored in the HDD 14C, and acquired by simply reading it.

  In the next step 58, based on the input color gamut outline information acquired in step 56, data of a large number of points located at different positions in the input color gamut on the second device-independent color space is generated as conversion conditions. Generate as input data group. In the next step 60, a constraint condition for the current color gamut conversion is acquired. For example, the constraint condition is acquired by causing the display device 20 to display a constraint condition selection screen in which a plurality of options for the constraint condition are specified and a message for requesting selection of any option is specified, and the keyboard 22 or When an operation for selecting any option is performed by the user via the mouse 24, it can be realized by performing processing for determining the option (constraint condition) selected by the user. Further, when an operation for selecting any option via the keyboard 22 or the mouse 24 is performed in advance by the user, and information indicating the option (constraint condition) selected in advance is stored in the HDD 14C. The constraint condition can be acquired by reading the information from the HDD 14C. Note that the keyboard 22 and the mouse 24 in the above aspect correspond to the setting means according to the present invention.

  When the restriction condition is acquired in step 60, the acquired restriction condition (restriction condition for the current color gamut conversion) is determined in the next step 62, and the process branches according to the determination result. In the present embodiment, there are two constraints for color gamut conversion: “input color reproduction emphasis” and “output color reproduction emphasis”. If the current color gamut conversion constraint is “input color reproduction emphasis”. If the restriction condition for the current color gamut conversion is “output color reproduction emphasis”, the process proceeds to step 66 to perform output color reproduction emphasis preprocessing. . In the following, first, pre-processing that emphasizes input color reproduction will be described with reference to FIG.

  In pre-processing that emphasizes input color reproduction, first, in step 80, a standard that defines the second device-dependent color space from the input color value group for generating the conversion conditions generated in step 58 of the color gamut conversion process (FIG. 4). The color value of one of the saturated colors of the color (primary) and its complementary color (secondary) is extracted as the color value of the reference input color used in the following processing. For example, when the second device is an image forming apparatus and the second device-dependent color space is a CMYK color space, the reference colors (primary) are C, M, Y, K, and their complementary colors (secondary) are R, G, B. In step 80, the color value of any one of C, M, Y, K, R, G, and B is extracted as the color value of the reference input color. Instead of the reference color that defines the second device-dependent color space and its complementary color, a reference color that defines the first device-dependent color space and its complementary color may be used. The reference input color corresponds to the predetermined color according to the present invention.

  In step 82, based on the output color gamut outline information, an equal hue plane (CUSP: see also FIG. 8A as an example) of the output color gamut having the same hue as the reference input color extracted in step 80 is extracted. In the next step 84, among the color values on the contour of the equi-hue surface of the output gamut having the same hue as the reference input color extracted in step 82, the color value having the smallest distance from the reference input color extracted in step 80. (The color value corresponding to the first color value described in claim 5: see also “color with the smallest distance from the reference input color (minJC)” shown in FIG. 8A). Set as the color value of the color.

  Note that the output-corresponding color is not limited to the above, and a color value having the same lightness as that of the reference input color is obtained on the contour of the uniform hue surface extracted in step 82, and the same lightness on the contour of the uniform hue surface is obtained. Color value whose distance from the color value is within a threshold value (color value corresponding to the second color value according to claim 5: “color whose distance from the color of equal brightness is within the threshold value” shown in FIG. 8A) May also be set as the color value of the output corresponding color of the standard input color.

  In addition, without extracting the same hue plane of the output gamut having the same hue as that of the reference input color (step 82), it is positioned on the outline of the output gamut in the second device-independent color space, and the second Vector distance from the reference input color in the device-independent color space (a color difference or a value of a predetermined evaluation function representing a distance in the second device-independent color space is applied as the vector distance) And a minimum color value (a color value corresponding to the third color value according to claim 5) is obtained and the color value is set as the color value of the output corresponding color of the reference input color. Good.

  Further, as the output corresponding colors of the reference input color, the first to third color values (“second device-independent color space out of the color values on the outline of the output color gamut and in the same hue as the reference input color”) are used. The first color value having the smallest distance above ”or“ the distance in the second device-independent color space from the color value of the same hue and lightness as the reference input color on the outline of the output color gamut Within the threshold value, on the outline of the output color gamut and on the second device-independent color space on the outline of the output color gamut and on the outline of the output color gamut and with the reference input color The arbitrary color value within the triangular color range on the second device-independent color space (the “third color value with the smallest vector distance”) having each vertex as a vertex. A color value corresponding to “a color value within a color range” may be applied. As the color value, for example, a value on a line connecting arbitrary two color values (for example, the first and second color values) in the second device-independent color space among the first to third color values. (For example, a color value corresponding to an average of two color values) or a color value located at an arbitrary position within the triangular color range obtained using the first to third color values (for example, first to first color values) Color value corresponding to the average of the third color values).

Further, which one of the first to third color values and the color value in the triangular color range is used as the output corresponding color of the reference input color is used as the color value (for example, hue) of the reference input color. You may make it switch according to it. This aspect corresponds to the invention described in claim 6 . As a result, the color value of the reference input color corresponding to the output can be optimized according to the color value (hue, etc.) of the reference input color. How to change the output corresponding color of the reference input color according to the color value of the reference input color may be determined in advance based on, for example, the result of an experiment or the like, but at least the reference input color is CIEL If the hue is within the range where b * <0 in the * a * b * color space, it is desirable to use the third color value as the output corresponding color of the reference input color.

  Further, when setting the output-corresponding color of the reference input color, at least when the third color value is used or there is a possibility as described above (that is, in the pre-processing that emphasizes input color reproduction, the reference input color When the third color value is fixedly used as the output corresponding color, the third color value is included in the output corresponding color switching options of the reference input color, and the third color value When there is a possibility that a color value within the triangular color range obtained based on a plurality of color values including the color corresponding to the output of the reference input color is used, the color gamut conversion processing according to this embodiment is performed. Before performing the conversion, the color value (at least lightness) of the image data is adjusted according to the output color gamut or the image output condition for the image data used for generating the conversion condition (for example, the input color value group for generating the conversion condition). Perform the range adjustment process and select the image to be output. It is desirable to incorporate the same range adjustment processing to the gamut conversion conditions used for converting the data (integrated conversion condition).

In the above range adjustment processing, for example, the maximum value and the minimum value of the brightness of the image data used for the generation of the conversion condition are matched with the maximum value and the minimum value of the brightness in the output color gamut in the second device-independent color space. Further, it may be a process of adjusting the color value of the image data used for generating the conversion condition. For example, the output device 18 (second device) according to the present embodiment is an image forming apparatus, and the color conversion process (first When the image data obtained through the color conversion, the second color conversion, the color gamut conversion, the third color conversion, and the fourth color conversion) is used for recording an image on a predetermined sheet, the conversion condition is generated. Processing for adjusting the color value of the image data used for generating the conversion condition so that white in the image data to be used matches the color of the predetermined paper (background color) (adjustment of the color value is performed in the CIEXYZ color space) Is appropriate) Good. The range adjustment process may be performed simultaneously with the first color conversion or the second color conversion, or may be performed during the color gamut conversion process (FIG. 4) according to the present embodiment. The above range adjustment processing corresponds to the invention described in claim 8 , and more appropriate color gamut conversion can be realized by performing the above range adjustment processing on the image data used for generating the conversion condition. Conversion conditions can be obtained.

  In step 86, the output correspondence color obtained in step 84 is converted by applying a conversion rule opposite to the conversion rule applied when setting (mapping) the color gamut conversion condition described later (the color gamut conversion condition The input corresponding color of the reference input color (FIG. 8B) is also obtained by performing an inverse conversion (corresponding to the inverse conversion described in claim 4) of the conversion (color gamut conversion) applying the conversion rule applied at the time of setting. Find the color value. In step 88, a vector distance (see also FIG. 8B) between the reference input color and the input corresponding color obtained in step 86 is calculated, and the calculated vector distance is used as the color value of the reference input color and the input corresponding color. And stored in the HDD 14C. In the next step 90, it is determined whether or not the processing in steps 80 to 88 described above has been performed for all the reference colors and their complementary saturated colors. If the determination is negative, the process returns to step 80, and steps 80 to 90 are repeated until the determination of step 90 is affirmed. As a result, the output corresponding color and the input corresponding color are respectively set, and the vector distances from the input corresponding color are calculated and stored, respectively, with all the reference colors and their saturated saturated colors as reference input colors.

  As described later, when “input color reproduction emphasis” is selected as the constraint condition for the color gamut conversion, for the reference input color, before changing the color value to the color value of the input corresponding color obtained in step 86. As described above, since the input corresponding color is obtained by performing reverse conversion of the color gamut conversion on the output corresponding color obtained in step 84, the reference input color is the pre-process. Thus, the color value (input corresponding color) converted to the output corresponding color is changed through the color gamut conversion. In addition, the color value (color value corresponding to the first color value or color value corresponding to the second color value according to claim 5) obtained as the output corresponding color in step 84 is the reference input color. Color values that satisfy the constraint of "input color reproduction emphasis" because they are the same hue, small in brightness and saturation with the reference input color, and located on the outline of the output color gamut The standard input color is changed to an input compatible color through pre-processing, and further converted to an output compatible color through color gamut conversion. Satisfactory color gamut conversion will be performed.

  Of the input color value group for generating conversion conditions, the reference color that defines the second device-dependent color space and the color value of one of its complementary colors (the color value of the reference input color) are often the case. Although there is a deviation from the output color gamut in the second device-independent color space, there may be a case where it is within the output color gamut from the beginning on the second device-independent color space. Then, for the reference input color that is within the output color gamut from the beginning in the second device-independent color space, the output corresponding color and the input corresponding color are sequentially obtained as described above, and the reference input color and the input corresponding color are determined. If the pre-processing for changing the color values of the reference input color and the surrounding color area according to the vector distance is performed, and further color gamut conversion is performed, the reference input color is converted into an output-corresponding color. By converting the colors in the color area around the reference input color to the corresponding color, the color gamut around the reference input color is unnaturally enlarged by pre-processing, and proper color reproduction is obtained. There is no problem.

  In consideration of this, in the processing of steps 80 to 90 described above, for example, in step 80, the reference color that defines the second device-dependent color space from the input color value group for generating the conversion condition and the saturated color of any of its complementary colors After extracting the color value as the color value of the reference input color, it is determined whether or not the extracted color value of the reference input color is within the output color gamut in the second device-independent color space, and the determination is denied. If the color value of the reference input color does not fall within the output color gamut, the process after the next step 82 is performed. On the other hand, if the determination is affirmative, the color of the input corresponding color of the reference input color The color value of the reference input color is set as the value as it is, the vector distance between the reference input color and the input corresponding color is set to 0, and these are stored in the HDD 14C in association with each other, and then steps 82 to 88 are skipped. It is preferably configured to perform the determination in step 90 and up. As a result, the pre-processing is not substantially performed on the reference input color whose color value in the second device-independent color space is within the output color gamut and the surrounding color gamut. Thus, the color gamut is preserved without unnaturally expanding the color gamut, and the reference input color and the colors in the surrounding color area can be appropriately reproduced.

In addition, when the color value of the reference input color is within the output color gamut in the second device-independent color space, instead of steps 82 and 84, the reference input is used as the color value of the output corresponding color of the reference input color. After performing the process of setting the color value of the color as it is, the process may move to step 86 to perform processes such as setting the input corresponding color of the reference input color and calculating the vector distance. In this case, for the reference input color and the surrounding color gamut whose color values in the second device-independent color space are within the output color gamut, the color gamut conversion is substantially performed in addition to the preprocessing. As a result, the reference input color and the colors in the surrounding color area can be appropriately reproduced. The above matters corresponds to the invention of claim 1 1, wherein.

  If the determination in step 90 is affirmative, the process proceeds to step 92, and the input not extracted as the reference input color from the input color value group for generating the conversion condition generated in step 58 of the color gamut conversion process (FIG. 4). One color value (color values of all reference colors and colors other than the saturated colors of the complementary colors) is extracted. In the next step 94, it is determined whether or not the input color value extracted in step 92 has the same hue as any of the plurality of color values previously extracted as the reference input color.

If the determination in step 94 is affirmative, the process proceeds to step 96, where the vector distance D ₀ between the input color value extracted in step 92 and the color value of the same hue (standard input color of the same hue) and the corresponding input color is set. A vector distance D between the input color value and the input corresponding color is obtained by multiplying the read vector distance by the ratio of the saturation C of the input color value to the saturation C ₀ of the reference input color having the same hue. The color value of the input corresponding color of the input color value is calculated based on the calculated vector distance, and the process proceeds to step 104.
D = D ₀ × (C / C ₀ )
Thereby, among the input color values extracted from the input color value group for generating the conversion condition, with respect to the input color value having the same hue as any of the plurality of color values extracted as the reference input color, A vector distance obtained by reducing the vector distance between the reference input color and the input corresponding color in accordance with the saturation ratio between the reference input color and the input color value (for example, “input color value and Also, a color value having a vector distance of input corresponding color ”is calculated and set as an input corresponding color.

On the other hand, if there is no color value having the same hue as the input color value extracted in step 92 among the plurality of color values previously extracted as the reference input color, the determination in step 94 is designated and the process proceeds to step 98. Transition. In the following, for convenience, among the plurality of color values extracted as the reference input color, as shown in FIG. 8C, the input color value is rotated clockwise around the lightness axis of the second device-independent color space. The color value of the hue closest to the hue of the color (color value corresponding to the first predetermined color according to claim 9 ) is referred to as a first reference input color, and is input counterclockwise about the lightness axis. The color value of the hue closest to the hue of the color value (color value corresponding to the second predetermined color according to claim 9 ) is referred to as a second reference input color.

  In step 98, a color value corresponding to the first reference input color is determined from among the plurality of color values extracted as the reference input color, and the determined first reference input color is determined in the same manner as in step 96 described above. The vector distance between the input color value and the input corresponding color is read from the HDD 14C, and the read vector distance is multiplied by the ratio of the saturation of the input color value to the saturation of the first reference input color. The vector distance with the input corresponding color is calculated, and the color value of the first input corresponding color of the input color value is calculated based on the calculated vector distance. In the next step 100, as in step 98, the color value corresponding to the second reference input color is determined from the plurality of color values extracted as the reference input color, and the determined second reference input color and its determined The vector distance from the input corresponding color is read from the HDD 14C, and the read vector distance is multiplied by the ratio of the saturation of the input color value to the saturation of the second reference input color. The vector distance to the color is calculated, and the color value of the second input corresponding color of the input color value is calculated based on the calculated vector distance.

  In step 102, the color corresponding to the weighted average of the color value of the first input corresponding color calculated in step 98 and the color value of the second input corresponding color calculated in step 100 (shown in FIG. 8C). The color corresponding to the intersection with the plane P) is calculated as the color value of the input corresponding color of the input color value, and the process proceeds to step 104. Note that as the weight in the weighted average, the hue difference between the input color value and the first input corresponding color, and the ratio of the hue difference between the input color value and the second input corresponding color can be used. Thereby, among the input color values extracted from the input color value group for generating the conversion condition, the input color values for which no color value of the same hue exists among the plurality of color values extracted as the reference input color are as follows: A vector distance obtained by subtracting the vector distance between the first reference input color and the input corresponding color in accordance with the saturation ratio between the first reference input color and the input color value, the second reference input color, and its input A vector distance corresponding to a weighted average of vector distances obtained by subtracting the vector distance from the corresponding color in accordance with the saturation ratio between the second reference input color and the input color value (for example, “input shown in FIG. 8C”) The color value of the input-corresponding color is calculated and set on the basis of “the vector distance between the color value and the input-corresponding color”.

  In step 104, it is determined whether or not the processing from step 92 has been performed on all input color values other than the reference input color in the input color value group for generating the conversion condition. If the determination is negative, the process returns to step 92, and steps 92 to 104 are repeated until the determination of step 104 is affirmed. As a result, the color values of the input corresponding colors are respectively calculated in step 96 or steps 98 to 102 for all the input color values other than the reference input color in the input color value group for generating the conversion condition.

  As described above, for input color values other than the reference input color, the color value of the input corresponding color is calculated without calculating the output corresponding color. For input-corresponding colors with input color values that have input colors, the color values are calculated based on the relationship (vector distance) between the reference input color with the same hue and the input-corresponding color, and there is a reference input color with the same hue. For input color values that are not, the relationship between the first reference input color that approximates the input color value and the hue and the input corresponding color (vector distance), and the second reference input color that approximates the input color value and the hue The color value of the input corresponding color is calculated based on the relationship between the input color and the input corresponding color (vector distance). Between the color value after color conversion (color value of the color corresponding to output) Without-up or the like is generated, it is possible to obtain a color value which is estimated to be converted into the proper color values also satisfy constraints "input color reproduction emphasized" simultaneously.

  When the color value group of the input corresponding color is obtained by calculating and setting the color value of the input corresponding color for all the input color values constituting the input color value group for generating the conversion condition, the determination in step 104 is performed. If the result is affirmative, the pre-processing emphasizing input color reproduction is terminated, and the routine proceeds to step 68 of the color gamut conversion processing (FIG. 4). Note that the color value of the input corresponding color obtained for each input color value by the above-described input color reproduction-oriented preprocessing (FIG. 7) is the constraint condition of “input color reproduction importance” for each input color value. The condition for associating each input color value with the color value of the corresponding input corresponding color corresponds to the “preprocessing condition” according to claim 2. Equivalent to.

  Next, with reference to FIG. 9, pre-processing that emphasizes output color reproduction will be described. In pre-processing that emphasizes output color reproduction, first, in step 120, the reference color value that defines the second device-dependent color space and the saturated color value of one of its complementary colors are used as the reference value from the input color value group for generating the conversion condition. Extracted as the color value of the input color. In the next step 122, the color value of the saturated color on the output side corresponding to the reference input color extracted in step 120 (for example, if the reference input color is Y and the second device is an image forming apparatus, it corresponds to the reference input color). The color value of the saturated color on the output color gamut side is the color value corresponding to the color value of the saturated color of Y in the output color gamut, that is, the color of the maximum density that can be formed only with the Y color material (toner, ink, etc.). ). In step 124, the color value of the reference input color extracted in step 120 is set as the color value of the input color.

In the next step 126, based on the output color gamut outline information, an equal hue plane (CUSP: see also FIG. 8A) of the output color gamut having the same hue as the input color for which the color value has been previously set is extracted. In the next step 128, among the color values on the contour of the equi-hue surface of the output gamut having the same hue as the input color extracted in step 126, the color value having the smallest distance from the input color (see FIG. 8A ). (See also “Minimum Distance from Reference Input Color (minJC)”) as the color value of the provisional output corresponding color of the reference input color. The provisional output-corresponding color of the reference input color is not limited to the above, and the color value of the input color and the lightness is obtained on the contour of the equal hue plane extracted in step 126, and And a color value whose distance from the color value of equal lightness is within the threshold value ( see also “color whose distance from the color of equal lightness is within the threshold value” shown in FIG. 8A ) is temporarily output as the standard input color The color value of the corresponding color may be set.

  In step 130, it is determined whether or not the saturation difference between the temporary output corresponding color value of the reference input color set in step 128 and the color value of the saturated color on the output side extracted in step 122 is equal to or smaller than a threshold value. In step 128, the color value having the minimum distance from the input color is calculated as the first temporary output corresponding color of the reference input color, and the second temporary output corresponding color of the reference input color is The distance between the input color and the color value of the lightness is within the threshold on the contour of the uniform hue plane, and the color value on the contour of the uniform hue plane is calculated, and the first temporary output corresponding color and the second temporary color are calculated. Of these output-corresponding colors, the provisional output-corresponding color that has a smaller saturation difference from the saturation color on the output side may be used for the determination in step 130.

  If the determination is negative, the process proceeds to step 132, and the input color is changed so that the hue of the input color changes by a certain amount in the direction approaching the saturated color on the output side (however, the lightness and saturation are the same as the reference input color). After changing the color value of the color, the process returns to step 126. Thereby, step 126 to step 132 are repeated until the determination in step 130 is affirmed. If the determination in step 130 is affirmed, the process proceeds to step 134, where the color value of the current temporary output-corresponding color is set to the color value of the output-corresponding color of the reference input color.

In setting the output corresponding color of the reference input color, the output color gamut in the second device-independent color space is used in the same manner as the third color value described above instead of steps 126 to 132 described above. A color value having a minimum vector distance from the reference input color in the second device-independent color space is obtained and set as the color value of the output corresponding color of the reference input color. You may do it.

Further, as a reference input color output corresponding color, and apply any color values in the triangular color range of the second device independent color space to each vertex of the fourth to color value of the sixth of the May be. As the color value, for example, a value on a line connecting arbitrary two color values (for example, the fourth and fifth color values) in the second device-independent color space among the fourth to sixth color values. (For example, a color value corresponding to the average of two color values) or a color value located at an arbitrary position within the triangular color range obtained using the fourth to sixth color values (for example, the fourth to sixth color values) Color value corresponding to the average of the sixth color values).

Further, which of the fourth to sixth color values and the color value within the triangular color range is used as the output corresponding color of the reference input color is used as the color value (for example, hue) of the reference input color. You may make it switch according to it . This ensures that the reference input color output corresponding color of the color values, it is possible to optimize according to the reference input color of the color values (such as hue). How to change the output corresponding color of the reference input color according to the color value of the reference input color may be determined in advance based on, for example, the result of an experiment or the like, but at least the reference input color is CIEL In the * a * b * color space, if the hue is within the range where b * <0, it is desirable to use the sixth color value as the output corresponding color of the reference input color.

Further, when setting the output-corresponding color of the reference input color, at least when the sixth color value is used or there is a possibility (that is, in the pre-processing that emphasizes output color reproduction, the reference input color is used) When the sixth color value is fixedly used as the output corresponding color, the sixth color value is included in the options for switching the output corresponding color of the reference input color, and the sixth color value The color gamut conversion processing according to the present embodiment is also performed in the case where there is a possibility that a color value in the triangular color range obtained based on a plurality of color values including the color corresponding to the output of the reference input color may be used. Before performing, the above-described range adjustment processing is performed on the image data (for example, input color value group for generating the conversion condition) used for generating the conversion condition, and the color gamut conversion condition used for converting the image data to be output The same range adjustment process is also used for (integrated conversion conditions). To incorporate is desirable. Thereby obtaining the conversion conditions varying with respect to the image data used for generating the conversion conditions that keep performing the above range adjustment process, it is possible to realize a more appropriate color gamut conversion.

  In step 136, the output corresponding color set in step 134 is converted by applying a conversion rule opposite to the conversion rule applied when setting the color gamut conversion condition, so that the color of the input corresponding color of the reference input color is obtained. Find the value. In step 138, the vector distance between the reference input color and the input corresponding color set in step 136 is calculated, and the calculated vector distance is stored in the HDD 14C in association with the reference input color and the color value of the input corresponding color. In the next step 140, it is determined whether or not the processes in steps 120 to 138 described above have been performed for all the reference colors and their complementary saturated colors. If the determination is negative, the process returns to step 120, and steps 120 to 140 are repeated until the determination of step 140 is affirmed. As a result, the output corresponding color and the input corresponding color are respectively set, and the vector distances from the input corresponding color are calculated and stored, respectively, with all the reference colors and their saturated saturated colors as reference input colors.

When “output color reproduction emphasis” is selected as the constraint condition for the color gamut conversion, pre-processing for changing the color value to the color value of the input corresponding color set in step 136 is performed for the reference input color. Since the input-corresponding color is obtained by performing inverse gamut conversion on the output-corresponding color set in step 134, the reference input color is set in step 134 through gamut conversion by preprocessing. It is changed to a color value (input corresponding color) converted to an output corresponding color. Further, the color value is set as output corresponding color in step 134, the reference input color and brightness and the difference in saturation is small, also the reference input color and equal hue as the input color initial hue, the determination in step 130 Since the hue of the input color is gradually approaching the saturated color on the output side until it is affirmed, the hue is as close as possible to the hue of the reference input color, but the saturation difference from the saturated color on the output side is within the threshold And color values that lie on the outline of the output color gamut, so color values that emphasize output color reproduction are compared to input-compatible colors set in input color reproduction-oriented preprocessing. Yes. For this reason, the reference input color is changed to the input corresponding color set in step 136 through pre-processing, and further converted into the output corresponding color set in step 136 through color gamut conversion. Therefore, the color gamut conversion satisfying the constraint condition of “emphasis on output color reproduction” is performed.

  In the processing of Steps 120 to 140 of the preprocessing that emphasizes output color reproduction, the color value of the reference input color set as the color value of the input color in Step 124 is the second before the processing of Step 126, for example. It is determined whether or not the output color gamut is within the device-independent color space, and if the determination is negative (if the color value of the reference input color does not fall within the output color gamut), the next step 126 and subsequent steps On the other hand, if the determination is affirmative, the color value of the reference input color is directly set as the color value of the input corresponding color of the reference input color, and the vector distance between the reference input color and the input corresponding color is set. Is set to 0, and these are associated with each other and stored in the HDD 14C. After that, it is preferable to perform the determination of step 140 by skipping steps 126 to 138. As a result, the pre-processing is not substantially performed on the reference input color whose color value in the second device-independent color space is within the output color gamut and the surrounding color gamut. Thus, the color gamut is preserved without unnaturally expanding the color gamut, and the reference input color and the colors in the surrounding color area can be appropriately reproduced.

Further, when the color value of the reference input color is within the output color gamut in the second device-independent color space, the reference color value of the output corresponding color of the reference input color is used as a reference instead of Step 126 to Step 134. After performing the process of setting the color value of the input color as it is, the process may proceed to step 136 to perform processes such as setting the input corresponding color of the reference input color and calculating the vector distance. In this case, for the reference input color and the surrounding color gamut whose color values in the second device-independent color space are within the output color gamut, the color gamut conversion is substantially performed in addition to the preprocessing. As a result, the reference input color and the colors in the surrounding color area can be appropriately reproduced. Note that corresponds to the invention also claim 1 1, wherein the matter.

  If the determination in step 140 is affirmative, the process proceeds to step 142, and one unextracted input color value is extracted as the reference input color from the input color value group for generating the conversion condition. In the next step 144, it is determined whether or not the input color value extracted in step 142 is located outside the output color gamut in the second device-independent color space. For this determination, as shown in FIG. 10, for example, based on the output color gamut outline information, the output hue gamut including the input color value is extracted, and the saturation on the extracted equal hue plane is maximized. Whether or not the contour point of the output color gamut is the same as the contour point and the color value on the lightness axis is set as the reference anchor, and whether or not the straight line connecting the input color value and the reference anchor intersects the contour of the output color gamut However, a determination method other than the above may be used.

If the input color value extracted in step 142 is located within the output color gamut, the determination in step 144 is denied and the process proceeds to step 146, where the input color value is used as the color value of the input color corresponding to the input color value. Set and go to step 158. As a result, among the input color values other than the reference input color in the input color value group, the color values located in the output color gamut in the second device-independent color space are substantially preprocessed. (Change of color value) is not performed (see also “no change of input color value” shown in FIG. 11), and only the color gamut conversion is performed. Therefore, the color gamut conversion is performed so that the color reproduction of the output is more important. Will be done. Note that eliminating the input color values that are located in the output color gamut as described above from the pre-processing of the subject corresponds to the invention of claim 1 0, wherein.

  On the other hand, if the input color value extracted in step 142 is located outside the output color gamut (within the “changed” area shown by hatching in FIG. 11), the determination in step 144 is affirmed and the process proceeds to step 148. In Steps 148 to 156, as in Steps 94 to 102 of the preprocessing emphasizing input color reproduction (FIG. 7), the input corresponding color of the input color value in which the reference input color having the same hue exists is the same hue. The color value is calculated and set based on the relationship (vector distance) between the reference input color and the input corresponding color, and for an input color value for which there is no uniform hue reference input color, the input color value and the hue are Based on the relationship between the first reference input color to be approximated and its input corresponding color (vector distance), and the relationship between the second reference input color whose color value and hue are approximated and its input corresponding color (vector distance) A force corresponding color of the color value after calculation-setting, the process proceeds to step 158.

  In step 158, it is determined whether or not the processing from step 142 onward has been performed for all input color values other than the reference input color in the input color value group for generating conversion conditions. If the determination is negative, the process returns to step 142, and steps 142 to 158 are repeated until the determination in step 158 is positive. As a result, the color values of the input corresponding color are set for all the input color values other than the reference input color in the input color value group for generating the conversion condition.

  In this way, even in preprocessing that emphasizes output color reproduction, input color values other than the standard input color and out of the output color gamut can be input without calculating output-compatible colors, as in the preprocessing that emphasizes input color reproduction. Although the color value of the color is calculated and set, in the pre-processing that emphasizes output color reproduction, the input corresponding color of the reference input color that is referenced when calculating the input corresponding color of the input color value Since the color value that satisfies the constraint condition is calculated and set, the above processing results in the input color corresponding to the input color value other than the reference input color as the input corresponding color after the gamut conversion of the reference input color. A color value that is estimated to be converted to an appropriate color value that does not cause a gap or the like between the color value (color value of the output-compatible color) and that satisfies the “output color reproduction emphasis” constraint at the same time. Obtainable.

  Note that, in the preprocessing that emphasizes output color reproduction according to the present embodiment, as described above, the input color value group for generating the conversion condition is located in the output color gamut in the second device-independent color space. For input color values, the input color value is set as the input corresponding color as it is, and for input color values located outside the output color gamut in the second device-independent color space, the standard of equi-hue Calculate / set the color value of the input corresponding color based on the relationship (vector distance) between the input color and the input corresponding color, or the relationship between the input color value and the first reference input color whose hue approximates the input corresponding color Since the color value of the input corresponding color is calculated and set based on (vector distance) and the relationship (vector distance) between the second reference input color that approximates the input color value and the hue and the input corresponding color, the second Depending on the shape difference between the input color gamut and output color gamut in the device-independent color space In the image represented by the image data that has undergone preprocessing and color gamut conversion according to the present embodiment, the color corresponding to the input color value positioned in the output color gamut in the second device-independent color space, and the second There is a possibility that a gradation gap may occur between colors corresponding to input color values located outside the output color gamut in the device-independent color space.

  In consideration of this, in the pre-processing that emphasizes output color reproduction, the calculation of the input corresponding color of the input color value located outside the output color gamut in the second device-independent color space (step 150 or steps 152 to 156) ), The calculation is controlled so that the lightness and saturation of the input-corresponding color become appropriate values that can suppress the above-described gradation gap (for example, the input color value and output in the second device-independent color space) The value changes according to the distance from the color gamut outline (this change may be a linear change or a non-linear change). Change the input-corresponding color (especially its hue) so that the key gap is suppressed. It is desirable to limit it to a value ) It may be.

  When the color value group of the input corresponding color is obtained by performing (calculation and setting) the color value of the input corresponding color for all the input color values constituting the input color value group for generating the conversion condition, step 158 is performed. This determination is affirmed, the preprocessing emphasizing output color reproduction is terminated, and the routine proceeds to step 68 of the color gamut conversion processing (FIG. 4). It should be noted that the color values of the input corresponding colors obtained for each individual input color value by the above-described preprocessing for emphasizing output color reproduction (FIG. 9) are the constraint conditions of “emphasis on output color reproduction” for each input color value. The condition for associating each input color value with the color value of the corresponding input corresponding color corresponds to the “preprocessing condition” according to claim 2. Equivalent to.

  When the preprocessing for emphasizing input color reproduction (FIG. 7) or the preprocessing for emphasizing output color (FIG. 9) is completed, in step 68 of the color gamut conversion processing (FIG. 4), the input color is based on the output color gamut outline information. The color values of the input corresponding colors are sequentially extracted one by one from the color value group of the input corresponding colors obtained by the preprocessing that emphasizes reproduction or the preprocessing that emphasizes output color reproduction, and the color gamut is converted to the color values of the input corresponding colors that have been extracted. Applying a predetermined conversion rule for condition generation, converting the position on the second device-independent color space so that it is within the output color gamut outline represented by the output color gamut outline information, An output data group for generating conversion conditions is generated by sequentially obtaining the output color values for the color values of all input-corresponding colors. Thereby, the color gamut conversion condition for converting the color value of the input corresponding color into the output color value is set.

  As the above conversion rule, a known conversion rule can be used in color gamut conversion (gamut mapping). For example, for a color value located in the output color gamut, the color value is directly used as the output color value. Used (the color value of the color corresponding to the input and the output color value are colorimetrically matched), and for the color value located outside the output color gamut, color conversion is performed so that it falls within the output color gamut and the output color value In order to preserve the relative relationship between points in the input color gamut and the paste type conversion rule to calculate the color value of all input-compatible colors, the compression / decompression type Conversion rules can be used. Also, in the paste type conversion rule, a method for projecting color values outside the output color gamut onto the outline of the output color gamut without changing the hue and brightness so that the lightness is preserved, and saturation preservation For this reason, there is a method of projecting a color value outside the output color gamut onto the outline of the output color gamut without changing the hue, and any of them may be used. As for compression / expansion conversion rules, there is a method of performing color gamut conversion so that gradation is preserved, and this may be applied. Furthermore, an adaptive conversion rule that applies a different conversion method for each region may be used. For example, a conversion rule that combines a pasting type and a compression / expansion type may be used.

  As described above, output color values for generating conversion conditions for all color values constituting the color value group of the input-corresponding colors obtained by the preprocessing that emphasizes input color reproduction or the preprocessing that emphasizes output color reproduction are respectively set. When determined, in the next step 70, each color value of the color value group of the input corresponding color is replaced with the corresponding input color value of the original input color value group for generating the conversion condition generated in the previous step 58. Thereafter, the input color value group and the output data group for generating the conversion condition generated in step 68 are associated with each other and set as conversion data in the CLUT. As a result, conversion from the input color value for generating the conversion condition to the color value of the input corresponding color (that is, pre-processing for emphasizing input color reproduction or output color reproduction) and conversion condition generation from the color value of the input corresponding color are performed. Conversion conditions for simultaneously performing conversion to output color values (that is, color gamut conversion under the color gamut conversion conditions set in step 68) are obtained, and pre-processing conditions emphasizing input color reproduction or output color reproduction are set in step 68. An integrated conversion condition in which the color gamut conversion conditions are integrated is generated (set in the CLUT).

  In step 72, an image to be output by the second device is represented, and image data (input data) that has undergone the first color conversion and the second color conversion (see FIG. 2) is converted into the CLUT in which the color gamut conversion conditions are set in step 70. Thus, pre-processing and color gamut conversion are simultaneously performed on the image data, and the color gamut conversion processing is completed. Of the above-described color gamut conversion processing, Step 68 to Step 72 correspond to the color gamut conversion means according to the present invention. Step 72 is a pre-processing for emphasizing input color reproduction (FIG. 7) and emphasizing output color reproduction. It corresponds to the pre-processing means which concerns on this invention with the pre-processing (FIG. 9).

  The image data that has been subjected to the preprocessing and the color gamut conversion as described above is output to the second device after the third color conversion and the fourth color conversion (see FIG. 2) are sequentially performed, and the image in the second device is output. Used for output. Thereby, the difference between the appearance of the image on the first device and the appearance of the image on the second device, which is caused mainly by the difference in color gamut between the first device and the second device, is corrected. Also, “input color reproduction emphasis” or “output color reproduction emphasis” is selected (set) as a constraint condition for color gamut conversion, but if the constraint condition is “input color reproduction emphasis”, pre-processing for emphasizing input color reproduction If the constraint condition is "Evaluation of output color reproduction", pre-processing that emphasizes output color reproduction is performed, so the original purpose of color gamut conversion is to fit the color gamut of the image data after color gamut conversion into the output color gamut. In addition, color gamut conversion that satisfies the set constraint conditions can be realized.

  In the present embodiment, the color value used for setting the color gamut conversion condition in step 68 is changed so as to satisfy the selected restriction condition by performing preprocessing according to the set restriction condition. Yes. For this reason, as an algorithm for realizing the setting of the color gamut conversion condition in step 68, it is not considered that the selected constraint is satisfied (a color that fits the color gamut of the image data after the color gamut conversion into the output color gamut). A general algorithm (satisfying the original purpose of the domain conversion) can be used, and there is no need to change the algorithm regardless of the contents of the constraints. On the other hand, although it is necessary to develop a pre-process corresponding to each constraint condition, the pre-process corresponding to the constraint condition is either a reference color (primary) that defines the second device-dependent color space or its complementary color (secondary). An output-compatible color that satisfies the constraint conditions is obtained from the color value of the saturated color (reference input color), and the reference input color is changed to a color value (input-compatible color) that is converted to an output-compatible color by gamut conversion. In addition, it can be realized by a relatively simple process of changing the input color value other than the reference input color according to the relationship between the reference input color and the input corresponding color. Therefore, the development load for realizing color gamut conversion that satisfies the set constraint conditions can be greatly reduced.

  Note that the content of the preprocessing according to the present invention is not limited to the content of the preprocessing emphasizing input color reproduction or the preprocessing emphasizing output color described above. For example, in the above description, in the preprocessing that emphasizes the reproduction of the input color, the aspect in which the output corresponding color of the reference input color and the input corresponding color are set to the same hue as the reference input color has been described. Even when “Input color reproduction is emphasized”, the output corresponding color of the reference input color and the hue of the input corresponding color are changed with respect to the reference input color under the condition that the hue difference with respect to the reference input color is within a predetermined value. It may be.

  Also, in the above, input color reproduction-oriented preprocessing or output color reproduction-oriented preprocessing is used to obtain input color reproduction-oriented or output color reproduction-oriented preprocessing conditions (color values of input-compatible colors that define the input processing). After setting the color gamut conversion condition using the color value group of the color, generate the integrated conversion condition that integrates the pre-processing condition and the color gamut conversion condition, and convert the image data according to this integrated conversion condition, so that the pre-processing However, the present invention is not limited to this, and after performing pre-processing (changing input color values) that satisfies the set constraints, the pre-processing is performed. A color gamut conversion that fits in the output color gamut may be performed on the passed color value.

  In the above description, two types of constraint conditions of “input color reproduction emphasis” and “output color reproduction emphasis” are described as examples of the constraint condition according to the present invention. However, the present invention is not limited to this, for example, There may be three or more types of constraints, “colorimetric” intended to reproduce colors as close as possible in colorimetry, “perceptual” intended to reproduce colors as closely as possible, and vivid eyes Constraints such as “saturation” intended to reproduce the color (with slightly increased saturation) may be provided.

  Furthermore, in the above description, the color gamut conversion program corresponding to the color processing program according to the present invention is stored (installed) in advance in the HDD 14C of the client terminal 14, but the color processing program according to the present invention is a CD- It is also possible to provide the information recorded in a recording medium such as a ROM or a DVD-ROM.

It is a block diagram which shows schematic structure of the computer system which concerns on this embodiment. It is the schematic which shows the flow of the color conversion process in this embodiment. It is the schematic which shows the flow of the 1st / 4th color conversion in a color conversion process. It is a flowchart which shows the content of a color gamut conversion process. It is the schematic which shows an example of the color gamut outline of the 2nd device in the color space depending on a 2nd device. It is the schematic which shows an example of the color gamut outline (output color gamut) of the 2nd device in a device independent color space. It is a flowchart which shows the content of the pre-process of emphasizing input color reproduction. It is the schematic for demonstrating the detail of the pre-processing of FIG. It is a flowchart which shows the content of the pre-process of emphasizing output color reproduction. It is the schematic for demonstrating an example of the inside / outside determination of an input color value. It is the schematic for demonstrating the detail of the pre-processing of FIG.

Explanation of symbols

10 Computer system 14 Client terminal 14A CPU
14B Memory 14C HDD
16 input devices 18 output devices

Claims (12)

Based on output color gamut information representing an output color gamut in a predetermined color space that does not depend on a specific device, a predetermined gamut of image data on the predetermined color space is included in the output color gamut. A color gamut conversion unit that sets a color gamut conversion condition for converting image data according to a conversion rule, and performs color gamut conversion of input image data according to the set color gamut conversion condition;
Setting means for setting a constraint condition for the color gamut conversion;
By the color gamut conversion by the color gamut conversion means, the color value of a predetermined color in the input image data is converted into an output corresponding color that satisfies the constraint condition set via the setting means. The color value of the predetermined color is changed, and the color value other than the color value of the predetermined color in the input image data is changed to a relationship between the color value before the change of the predetermined color and the color value after the change. Pre-processing means for performing pre-processing to be changed in response,
Including color processing device. The preprocessing means performs the preprocessing on individual color values in an input color gamut corresponding to a color reproduction gamut of input image data on the predetermined color space;
The color gamut conversion unit sets the color gamut conversion condition based on individual color values that have undergone the preprocessing by the preprocessing unit,
The pre-processing conditions for associating the values before and after the change of the individual color values in the pre-processing by the pre-processing means and the color gamut conversion conditions set by the color gamut converting means are integrated. An integrated conversion condition is generated, and individual color values of the input image data are converted in accordance with the generated integrated conversion condition, whereby the preprocessing by the preprocessing unit and the color gamut conversion unit for the input image data The color processing apparatus according to claim 1, wherein the color gamut conversion is performed simultaneously.   The predetermined color is a color space of input image data before being converted to image data of the predetermined color space, or a reference color that defines a color space depending on a specific device to which image data is output and its complementary color The color processing apparatus according to claim 1, wherein the color processing apparatus is a saturated color of at least one of the colors.   The preprocessing means obtains a color value of an output corresponding color satisfying the set constraint condition from the color value of the predetermined color, and based on the predetermined conversion rule for the obtained color value of the output corresponding color The color value of the input-corresponding color is obtained by performing inverse conversion of the conversion, and the color value of the predetermined color is changed by replacing the color value of the predetermined color with the color value of the input-corresponding color. The color processing apparatus according to claim 1. The constraints set via the setting means include constraints that place importance on color reproduction of the input,
The preprocessing means, when a constraint condition that places importance on input color reproduction is set via the setting means, as a color value of an output corresponding color that satisfies the constraint condition, on the outline of the output color gamut The first color value having the smallest distance in the predetermined color space among the color values having the same hue as the color value of the predetermined color, or on the outline of the output color gamut and of the predetermined color A second value of the same hue as the color value of the predetermined color on the outline of the output color gamut and within a threshold distance from the reference color value having the same hue and lightness as the color value within the threshold. Or the third color value having the smallest vector distance between the color value of the predetermined color and the predetermined color space on the outline of the output color gamut, or the first to third color values. 5. The color according to claim 4, wherein a color value within a triangular color range on the predetermined color space with each color value as a vertex is obtained. Management apparatus. 6. The color processing according to claim 5, wherein the preprocessing means switches between the plurality of types of color values to be used as a color value of an output-corresponding color that satisfies the constraint condition, according to the predetermined color. apparatus. When the predetermined color is a hue within a range where b * <0 in the CIE L * a * b * color space, the pre-processing unit sets the first color as an output corresponding color value satisfying the constraint condition. 7. The color processing apparatus according to claim 6, wherein a color value of 3 is used. For the input image data whose color value is changed by the pre-processing means, a range adjustment process for adjusting at least the brightness of the color values of the input image data in accordance with the output color gamut or image output condition is performed in advance. The color processing apparatus according to claim 1, wherein the color processing apparatus is performed. The pre-processing means, for color values other than the color value of the predetermined color, for the color value to be changed in hue equal to the predetermined color, the color value before the change of the predetermined color and the color value after the change A vector distance obtained by subtracting a vector distance from a color value according to a saturation ratio between the color value before the change of the predetermined color and the color value to be changed is obtained, and the vector distance is calculated based on the obtained vector distance. The color value of the change target is changed, and for the color value of the change target in which the predetermined color having the same hue does not exist, the color value before the change of the first predetermined color whose hue approximates the color value of the change target The first vector distance obtained by reducing the vector distance between the color value and the color value after the change according to the saturation ratio between the color value before the change of the first predetermined color and the color value to be changed. And a color value before the change and a color value after the change of the second predetermined color whose hue is approximate to the color value to be changed A second vector distance obtained by reducing the vector distance in accordance with a saturation ratio between the color value before the change of the second predetermined color and the color value of the change target is obtained, and the color value of the change target The first vector distance and the second vector distance according to the hue difference between the color value before the change of the first predetermined color and the color value before the change of the second predetermined color. The color processing apparatus according to claim 1, wherein a weighted average value is calculated, and the color value to be changed is changed based on a vector distance corresponding to the calculated weighted average value. The pre-processing unit outputs an output color in the predetermined color space among color values other than the color value of the predetermined color when a constraint condition that emphasizes output color reproduction is set via the setting unit. The color processing apparatus according to claim 9, wherein the color value is changed only for out-of-range color values as the change target. 2. The preprocessing means excludes, from among the predetermined colors, colors whose color values are within an output color gamut in the predetermined color space from color value change targets. Color processing equipment. Computer
Based on output color gamut information representing an output color gamut in a predetermined color space that does not depend on a specific device, a predetermined gamut of image data on the predetermined color space is included in the output color gamut. Color gamut conversion means for setting a color gamut conversion condition for converting image data according to a conversion rule, and performing color gamut conversion of input image data according to the set color gamut conversion condition,
Setting means for setting a constraint condition for the color gamut conversion;
In addition, the color gamut conversion by the color gamut conversion unit converts the color value of a predetermined color in the input image data into an output corresponding color that satisfies the constraint condition set via the setting unit. The color value of the predetermined color is changed, and the color value other than the color value of the predetermined color in the input image data is changed between the color value before the change of the predetermined color and the color value after the change. Preprocessing means for performing preprocessing to be changed according to the relationship
Color processing program to function as.

Images