JP6665559B2 - Calculation device and computer program - Google Patents

Description

  The present disclosure relates to a technique for calculating a color specification value in a second color space corresponding to a color specification value in a first color space.

  2. Description of the Related Art Conventionally, in image processing such as printing, color conversion processing for converting a color space of image data has been performed. In such a color conversion process, information that defines a correspondence between two color spaces, such as a color conversion table, is used. Here, in order to make the black tone jump inconspicuous, a new intermediate parameter is generated by performing a linear interpolation operation on the intermediate parameter output from the color conversion table, and the black output color is calculated based on the new intermediate parameter. Techniques for generating values have been proposed.

JP 2002-44474 A

  By the way, when an achromatic color material is used in an area where an achromatic color material such as black should not be used (for example, a bright area), image quality (for example, granularity) may be reduced.

  The present specification discloses a technique capable of suppressing a decrease in image quality in an area where an achromatic color material should not be used.

  This specification discloses, for example, the following application examples.

[Application Example 1]
A second type of color value, which is a color value in the second color space, corresponding to a first type of color value, which is a color value in the first color space, is calculated using the color correspondence information. In the calculation device, the color correspondence information includes a plurality of first type representative color values in the first color space, a plurality of second type representative color values in the second color space, The calculation device is information that associates
The second type color value is represented by a plurality of color components corresponding to the plurality of types of color materials including an achromatic color material and a plurality of types of color materials used for printing,
The plurality of first-type representative color values include a plurality of achromatic representative values on an achromatic line connecting white and black in the first color space,
The plurality of achromatic representative values are a high-brightness representative value and a low-brightness representative value adjacent to each other on the achromatic color line, and the high-brightness representative value having a relatively high brightness, and the relatively low brightness. And a low brightness representative value,
The high brightness representative value and the low brightness representative value sandwich a reference color value on the achromatic color line,
The reference color value is the blackest among the first type color values on the achromatic line associated with the second type color value in which the value of the color component of the achromatic color material is zero. And a color specification value different from any of the plurality of achromatic representative values,
The calculation device,
A second type color value corresponding to a first type color value between the reference color value on the achromatic color line and the high lightness representative value is a second color value corresponding to the low lightness representative value. A first calculation unit that calculates using a second type color value associated with the high brightness representative value without using a type color value;
A second type color value corresponding to a first type color value between the reference color value on the achromatic color line and the low lightness representative value is a second type color value associated with the low lightness representative value. A second calculating unit that calculates using the seed color value,
A calculation device comprising:

  According to this configuration, the calculation of the second type color value corresponding to the first type color value between the reference color value on the achromatic color line and the high value representative value is associated with the low value representative value. Instead of using the assigned second type color value, the second type color value associated with the high brightness representative value is used. The color component of the achromatic color material of the second type representative color value corresponding to the low brightness representative value may exceed zero, but the achromatic color material of the second type representative color value corresponding to the high brightness representative value Has a zero color component. Therefore, in the second type color value corresponding to the first type color value between the reference color value and the high brightness representative value, the color component corresponding to the achromatic color material is unintentionally set to zero. Can be suppressed from becoming larger. Further, the calculation of the second type color value corresponding to the first type color value between the reference color value on the achromatic color line and the low value representative value is performed by the second value associated with the low value representative value. Since the seed color value is used, an appropriate second seed color value can be calculated.

  The technology disclosed in the present specification can be realized in various modes. For example, a calculation method and a calculation device, a computer program for realizing the functions of the method or the device, and a computer program It can be realized in the form of a recorded recording medium (for example, a non-temporary recording medium).

FIG. 1 is an explanatory diagram illustrating a data processing device 100 according to an embodiment. 9 is a flowchart illustrating an example of processing for creating a lookup table LUT. FIG. 3 is an explanatory diagram of a color solid CC represented by RGB color components. FIG. 4 is an explanatory diagram illustrating a relationship between a color specification value on an achromatic line AL and a gradation value of CMYK. 13 is a flowchart illustrating an example of a gray adjustment process. 9 is a flowchart of an example of a process for calculating an adjusted colorimetric value of CMYK. FIG. 9 is an explanatory diagram of CMYK color values corresponding to grid values separated from an achromatic line AL. 9 is a flowchart illustrating an example of a procedure of a printing process. 9 is a flowchart illustrating an example of a procedure of a color conversion process.

A. First embodiment:
FIG. 1 is an explanatory diagram illustrating the data processing device 100 according to the embodiment. The data processing device 100 is, for example, a personal computer (for example, a desktop computer, a tablet computer). The data processing device 100 includes a processor 110, a volatile storage device 120, a nonvolatile storage device 130, a display unit 140 that displays an image, an operation unit 150 that accepts an operation by a user, and an interface 190. ing. These elements are connected to each other via a bus.

  The processor 110 is a device that performs data processing, and is, for example, a CPU. The volatile storage device 120 is, for example, a DRAM, and the non-volatile storage device 130 is, for example, a flash memory.

  The nonvolatile storage device 130 stores a first program 132, a second program 134, and a third program 136. The processor 110 realizes various functions by executing the programs 132, 134, and 136. Details of the functions realized by these programs 132, 134, 136 will be described later. The processor 110 temporarily stores various intermediate data used for executing the programs 132, 134, and 136 in a storage device (for example, one of the volatile storage device 120 and the nonvolatile storage device 130).

  The display unit 140 is a device that displays an image, and is, for example, a liquid crystal display. The operation unit 150 is a device that receives an operation by a user, and is, for example, a touch panel that is disposed on the display unit 140 in an overlapping manner. The user can input various instructions to the data processing device 100 by operating the operation unit 150.

  The interface 190 is an interface for communicating with another device (for example, a USB interface, a wired LAN interface, and an IEEE802.11 wireless interface). The colorimeter 200 and the printer 210 are connected to the interface 190. The colorimeter 200 is a device that measures colors and outputs colorimetric values, and is, for example, a spectral colorimeter. The printer 210 is a device that prints an image on paper (an example of a print medium). In the present embodiment, the printer 210 is an inkjet printing apparatus that uses respective inks of cyan C, magenta M, yellow Y, and black K. In addition, as the printer 210, a printing device of another system (for example, a laser system) may be adopted.

  FIG. 2 is a flowchart illustrating an example of processing for creating a lookup table LUT for a printer. In this embodiment, the look-up table LUT is used when printing an image using image data expressed in the RGB color space. The look-up table LUT includes a plurality of color values represented by tone values of each color component of RGB and a plurality of color values represented by tone values of each color component of a plurality of color materials usable in the printer. Is a table that determines the correspondence between. Here, it is assumed that four types of color materials, cyan C, magenta M, yellow Y, and black K, can be used as the plurality of color materials. Further, it is assumed that the respective gradation values of RGB and CMYK are represented in 256 levels from 0 to 255. The CMYK gradation value is larger as the amount of the corresponding color material per unit area is larger. Hereinafter, the RGB color values are also referred to as first type color values. The CMYK color values are also referred to as second type color values.

  FIG. 3 is an explanatory diagram of a color solid CC represented by RGB color components. Each of the eight vertexes of the color solid CC is assigned a code indicating a color (specifically, a black vertex Vk (0, 0, 0), a red vertex Vr (255, 0, 0), a green vertex) Vertex Vg (0, 255, 0), blue vertex Vbl (0, 0, 255), cyan vertex Vc (0, 255, 255), magenta vertex Vm (255, 0, 255), yellow vertex Vy (255, 255) , 0), white vertex Vw (255, 255, 255)). The numbers in parentheses indicate the values of the respective color components (red R, green G, blue B).

  In this embodiment, the look-up table LUT is associated with a plurality of representative color values (also referred to as grid values) in the RGB color space and a plurality of color values in the CMYK color space, and is associated with the plurality of grid values. And a plurality of specified color values. The grid value is, for example, a value obtained by setting each of the RGB values to any one of 33 specific values approximately uniformly arranged between 0 and 255 in the RGB color space. In the present embodiment, such a plurality of grid values are approximately uniformly distributed in the color solid CC of FIG. 3 (not shown).

  In the figure, a first line RL1, a second line RL2, and an achromatic line AL are shown. The first line RL1 is a straight line connecting the white vertex Vw and the red vertex Vr. The second line RL2 is a straight line connecting the red vertex Vr and the black vertex Vk. These lines RL1 and RL2 are straight lines on the outer shell of the color solid CC. The achromatic line AL is a straight line connecting the white vertex Vw and the black vertex Vk. On the achromatic line AL, R = G = B. The color values on the achromatic line AL indicate achromatic colors. The color values on the triangular area RA surrounded by the three lines RL1, RL2, and AL represent a color having a red hue. Generally, in a plane including the achromatic color line AL in the color solid CC, a portion on one side when viewed from the achromatic color line AL represents a color having substantially the same hue.

  The processor 110 (FIG. 1) calculates a plurality of colorimetric values in the CMYK color space corresponding to a plurality of grid values in the RGB color space by executing the processing in FIG. 2 is executed by the processor 110 operating according to the first program 132. The color measurement using the colorimeter 200 is performed by the processor 110 that operates according to the second program 134 for color measurement. Printing of an image using the printer 210 is performed by the processor 110 that operates according to the third program 136 for printing.

  In S100, the processor 110 (FIG. 1) creates calibration data. The calibration data is data for correcting the CMYK gradation values so that the density of the actually printed color changes linearly with respect to each change in the CMYK gradation values. In the present embodiment, the calibration data includes the correspondence between the pre-correction gradation value Ca for cyan and the corrected gradation value Cb, and the correspondence between the pre-correction gradation value Ma for magenta and the corrected gradation value Mb. And the corresponding relationship between the yellow uncorrected tone value Ya and the corrected tone value Yb, and the corresponding relationship between the black uncorrected tone value Ka and the corrected tone value Kb. For example, a one-dimensional lookup table is used as data representing the correspondence between the pre-correction gradation value and the corrected gradation value. The calibration data includes four one-dimensional look-up tables for the four CMYK color components.

  The calibration data is generated, for example, as follows. Hereinafter, an example of a method of creating a one-dimensional lookup table for cyan C will be described. The processor 110 causes the printer 210 to print a plurality of cyan C calibration patches in accordance with the third printing program 136. One patch corresponds to one tone value of cyan C, and is an area where the density printed with the cyan C color material is uniform. Among the plurality of patches, the corresponding cyan C tone values (that is, densities) are different from each other. Hereinafter, a plurality of tone values corresponding to a plurality of patches are also referred to as a plurality of representative values for calibration. The plurality of representative values for calibration are approximately equally selected from, for example, a range from a minimum value (here, zero) to a maximum value (here, 255).

  The processor 110 generates print data using patch image data representing a plurality of patches according to the third program 136 for printing, and supplies the generated print data to the printer 210. The printer 210 prints a plurality of patches according to the received print data. In this embodiment, the patch image data is represented in the CMYK color space. The third program for printing 136 has a function of generating print data by performing halftone processing (for example, error diffusion processing or processing using a dither matrix) using CMYK gradation values. Cause the processor 110 to execute. The patch is printed according to the print data generated by the halftone processing. The patch image data is prepared in advance. Alternatively, the processor 110 operating according to the first program 132 may generate the patch image data in S100.

  The processor 110 causes the colorimeter 200 to perform colorimetry on a plurality of printed patches according to the second colorimetric program 134, and specifies the optical density of each patch. Thus, the relationship between the tone value of cyan C and the actual optical density is specified. It should be noted that a target density is associated in advance with each of the plurality of representative values of cyan C. The processor 110 calculates a tone value that achieves the target density previously associated with the representative value from the relationship between the tone value and the actual optical density according to the first program 132 for creating the LUT (for example, interpolation). ). The calculation of the gradation value for realizing the target density is performed for each representative value. Thus, the correspondence between the representative value and the gradation value that achieves the target density is determined for each representative value. The processor 110 uses the representative value as the pre-correction gradation value Ca, and uses the gradation value that realizes the target density associated with the representative value as the corrected gradation value Cb, thereby obtaining the one-dimensional look for cyan C. Create an uptable. Calibration data is similarly created for the other color components M, Y, and K.

  In S110 of FIG. 2, the processor 110 specifies an achromatic representative value for a patch on the achromatic line AL (also referred to as a patch representative value). The patch representative value is a part of a plurality of grid values among a plurality of grid values located on the achromatic line AL of the color solid CC described with reference to FIG. 3 and is a grid value used for printing a patch described later. is there. FIG. 4 is an explanatory diagram showing the relationship between the color values on the achromatic line AL and the CMYK gradation values. The horizontal axis indicates the position of the color specification value on the achromatic line AL, and the vertical axis indicates the CMYK gradation values. The position of the color specification value is represented by a gray value GV representing a distance from the white vertex Vw. The gray value GV is expressed in a range from zero indicating the position of the white vertex Vw to 255 indicating the position of the black vertex Vk. The color values on the achromatic line AL can be specified by the gray value GV. Hereinafter, the description will be given using the same reference numerals as the reference values of the color values on the achromatic line AL as the reference values of the gray values of the specification values.

  The plurality of black points shown on the horizontal axis indicate the plurality of patch representative values specified in S110. In this embodiment, ten achromatic grid values of gray values GV = 16, 32, 48, 80, 112, 144, 176, 208, 240, 255 are used as patch representative values.

  The CMYK tone values in FIG. 4A indicate predetermined unadjusted tone values. The unadjusted gradation value represents a reference of the CMYK gradation value corresponding to the color specification value on the achromatic color line AL. In the present embodiment, data representing the correspondence between a plurality of patch representative values and the unadjusted gradation values of CMYK is stored in advance in the nonvolatile storage device 130 together with the first program 132 (not shown). The graph of FIG. 4A is specified by interpolating such a correspondence.

  As shown in the figure, in the color range where the gray value GV is equal to or less than the predetermined reference value Gk (here, 64), the gradation value of black K is zero. The CMY tone values increase from zero as the gray value GV increases from zero. Thus, in the color range where the gray value GV is less than the reference value Gk, that is, in the bright color range including the white vertex Vw, the tone value of the black K is zero because the black K dot is conspicuous. This is for suppressing.

  In this embodiment, it is assumed that an achromatic color is expressed by an equal amount of color mixture of cyan C, magenta M, and yellow Y. Therefore, the three unadjusted tone values of CMY associated with the color values on the achromatic line AL are the same.

  In a color range in which the gray value GV is equal to or larger than the reference value Gk, the grayscale value of the black K increases from zero as the gray value GV increases from the reference value Gk. The ratio of the increase in the CMY tone value to the increase in the gray value GV gradually decreases as the gray value GV increases from the reference value Gk. Then, in some color ranges including the black vertex Vk, the CMY tone values decrease as the gray value GV increases. As described above, in the color range in which the gray value GV is equal to or larger than the reference value Gk, that is, in the dark color range including the black vertex Vk, the increase in CMY is suppressed and K increases. Can be reduced.

  The reference value Gk is determined in advance according to the characteristics of the color material so that the black K dots are not conspicuous in the bright region and the total amount of the color material is suppressed from increasing in the dark region. I have. Therefore, when creating the lookup table, when the achromatic line AL is traced from the white vertex Vw to the black vertex Vk, the position where the gradation value of the black K changes from zero to a value larger than zero is determined. , Is preferably maintained unchanged from the reference value Gk.

  In the actual printer 210, the balance of the amount of color material used for printing among a plurality of available color materials (here, CMYK) can deviate from the assumed balance. For example, the amount of the cyan C color material may be larger than expected. In this case, when the color represented by the color specification value on the achromatic line AL is printed, a bluish color may be printed instead of the achromatic color. Such a deviation in the amount of the color material may be different for each model of the printer 210. Further, the deviation of the amount of the color material may be different for each individual printer 210.

  In S120 of FIG. 2, the processor 110 performs a gray adjustment process for correcting a shift in a printed color due to such a shift in the amount of the color material. The gray adjustment process is a process of adjusting the CMYK gradation values so that the color represented by the color specification value on the achromatic line AL is printed in achromatic color.

  FIG. 5 is a flowchart illustrating an example of the gray adjustment process. In S210, the processor 110 prints a plurality of patches for each of the plurality of patch representative values described in FIG. In the present embodiment, the processor 110 causes the printer 210 to print a plurality of patches associated with each patch representative value. For a plurality of patches associated with one patch representative value, the gradation value is changed in five steps centering on the unadjusted gradation value (FIG. 4A) associated with the patch representative value. It is obtained by For example, the five tone values of cyan C are represented as follows using the adjustment width d and the unadjusted tone value Ci of cyan associated with the patch representative value. Ci-2d, Ci-d, Ci, Ci + d, Ci + 2d. The adjustment width d is determined in advance. The five gradation values of the other color components M, Y, and K are similarly represented. In this embodiment, the gradation value of the color component having the unadjusted gradation value larger than zero is changed in five steps. For example, when K = 0 and CMY> 0, since the three gradation values of CMY change in five steps, the total number of patches is 5 × 5 × 5 = 125. In any of the 125 patches, the black K tone value is maintained at zero. If all of CMYK are larger than zero, the four gradation values of CMYK change in five steps, and the total number of patches is 5 × 5 × 5 × 5 = 625. Hereinafter, a plurality of CMYK color values representing a plurality of patches are also referred to as patch color values.

  If the tone value becomes less than zero as a result of changing the tone value according to the adjustment width d, printing of a patch represented by a tone value less than zero is omitted. Instead, the adjustment width d may be reduced so that the gradation value after the change becomes zero or more. Also, as a result of changing the gradation value according to the adjustment width d, if the gradation value exceeds the maximum value (255 in this case) of the range that the gradation value can take, the gradation value exceeds the maximum value. Printing of the represented patch is omitted. Instead, the adjustment width d may be reduced so that the changed tone value is equal to or less than the maximum value.

  The processor 110 generates print data using gray adjustment patch image data representing a plurality of patches by a plurality of CMYK patch color values in accordance with the third program 136, and prints the generated print data to the printer 210. To supply. The printer 210 prints a plurality of patches according to the received print data. Here, the gradation value of the patch color specification value (that is, the gradation value represented by using the unadjusted gradation value and the adjustment width d) is used as the pre-correction gradation value described in S100 of FIG. Can be The processor 110 converts the tone values of the patch color values into corrected tone values using the calibration data, and generates print data by halftone processing of the corrected tone values. Note that patch image data for gray adjustment is prepared in advance. Alternatively, the processor 110 operating according to the first program 132 may generate the patch image data in S210.

  In S220, the processor 110 causes the colorimeter 200 to measure the colors of the plurality of printed patches according to the second program 134 for colorimetry, and specifies the colorimetric value of each patch. The colorimetric value is a colorimetric value in a color space independent of a device such as a printer, and in this embodiment, is a colorimetric value in a CIELAB color space (hereinafter also referred to as a Lab value). Thereby, the correspondence between the plurality of patch color values (CMYK) and the colorimetric values (L * a * b *) is specified.

  In S223, the processor 110 selects one unprocessed patch representative value from the plurality of patch representative values described with reference to FIG. Hereinafter, the selected patch representative value is also referred to as a noted representative value. In S226, the processor 110 specifies a plurality of colorimetric values obtained from a plurality of patches associated with the noted representative value among all the colorimetric values of all the patch representative values acquired in S220. . Hereinafter, the plurality of patches associated with the noted representative value are also referred to as a plurality of noted patches, and the plurality of colorimetric values obtained from the plurality of noted patches are also referred to as a plurality of noted patch colorimetric values.

  A target color value, which is a target colorimetric value, is associated in advance with the target representative value (and, consequently, each of the plurality of patch representative values). In S230 of FIG. 5, the processor 110, in accordance with the first program 132 for creating the LUT, assigns the CMYK color values for realizing the target color value previously associated with the target representative value to each of the plurality of target patches. It is calculated using the correspondence between the patch colorimetric value (CMYK) and the target patch colorimetric value (L * a * b *). In the present embodiment, the processor 110 forms the smallest triangle T surrounding the target color value CVx among the plurality of colorimetric values CV projected on the a * b * plane, as shown in the lower part of FIG. The CMYK colorimetric values corresponding to the target color values are calculated by area-interpolating the three CMYK colorimetric values corresponding to the three colorimetric values CV. Hereinafter, the calculated CMYK color values are also referred to as adjusted color values. The adjusted color values of CMYK correspond to the gradation values before correction described in S100 of FIG. As a method of calculating the adjusted colorimetric values of CMYK, various other methods for specifying the CMYK colorimetric values using at least one of the plurality of colorimetric values can be adopted. is there. For example, triangular pyramid interpolation for interpolating four CMYK colorimetric values corresponding to four colorimetric values forming a minimum triangular pyramid including a target color value may be employed. Further, a CMYK colorimetric value associated with a colorimetric value closest to the target color value in the CIELAB color space may be adopted as a CMYK adjusted colorimetric value corresponding to the target color value.

  In S240, the processor 110 determines whether or not processing of all patch representative values (that is, achromatic representative values for patches) has been completed. If unprocessed patch representative values remain (S240: No), the processor 110 proceeds to S223 and executes processing of unprocessed patch representative values. When the processing of all the patch representative values is completed (S240: Yes), in S250, the processor 110 causes the CMYK for a plurality of achromatic grid values other than the patch representative values on the achromatic line AL (FIG. 3). Is calculated.

  FIG. 6 is a flowchart of an example of processing for calculating the adjusted colorimetric values of CMYK. The processing in FIG. 6 is executed by the processor 110 that operates according to the first program 132 for creating an LUT. In S320, the processor 110 specifies the reference value Gk described with reference to FIG. As described above, the RGB color value (also referred to as the reference color value Gk) represented by the reference value Gk is such that when the gray value GV is increased from the white vertex Vw, the gradation value of the black K becomes zero. From 0 to a value larger than zero (also referred to as a K generation level). In other words, the reference color value Gk is the blackest vertex Vk among the RGB color values on the achromatic line AL associated with the CMYK color value whose black K gradation value is zero. Near color values.

  In S323, the processor 110 selects one unprocessed achromatic grid value from among the unprocessed achromatic grid values, that is, the achromatic grid values for which the CMYK adjusted colorimetric values have not been calculated. . Hereinafter, the gray value of the selected achromatic color grid value is also referred to as a target gray value Gx. The selected achromatic grid value is also referred to as an achromatic grid value Gx using the same reference Gx.

  In S326, the processor 110 specifies two achromatic representative values G1 and G2 sandwiching the target gray value Gx. The first achromatic representative value G1 is a patch representative value next to the high lightness side (that is, the white vertex Vw side) when viewed from the target gray value Gx. The second achromatic representative value G2 is a patch representative value next to the low brightness side (that is, the black vertex Vk side) when viewed from the target gray value Gx.

  In S330, the processor 110 determines whether or not the reference value Gk is located between the two achromatic representative values G1 and G2. When the reference value Gk is not located between the two achromatic representative values G1 and G2 (S330: No), that is, the reference value Gk is located closer to the black vertex Vk than the second achromatic representative value G2. In the case and the case where the reference value Gk is located closer to the white vertex Vw than the first achromatic representative value G1, the processor 110 proceeds to S340. In S340, the processor 110 calculates an adjusted CMYK color value corresponding to the target gray value Gx by interpolating the adjusted CMYK color values of the two achromatic representative values G1 and G2. . Then, the processor 110 proceeds to S380.

  The graph of FIG. 4B shows the positions of the color values on the achromatic line AL and the adjusted color values of CMYK calculated by the processes of FIGS. 5 and 6 (that is, each adjusted gradation of CMYK). Values) are shown. The high lightness representative value Gw in the figure is a patch representative value next to the high lightness side (that is, the white vertex Vw side) of the reference value Gk. The low brightness representative value Gb is a patch representative value adjacent to the low brightness side of the reference value Gk (that is, the black vertex Vk side).

  The first range R1 is a color range on the high lightness side from the high lightness representative value Gw. When the target gray value Gx is located within the first range R1, the two achromatic representative values G1 and G2 sandwiching the target gray value Gx are selected from within the first range R1, so that the reference value Gk is 2 It is not located between the achromatic representative values G1 and G2. Accordingly, the adjusted gradation value of CMYK corresponding to the target gray value Gx in the first range R1 is calculated in S340. As described above, the first range R1 is a color range on the higher lightness side than the reference value Gk. Since the two achromatic representative values G1 and G2 used for the interpolation are selected from the first range R1, the adjusted gradation value of the black K of each of the two achromatic representative values G1 and G2 is zero. It is. As a result, the adjusted gradation value of black K calculated by interpolation is also zero. That is, within the first range R1, the adjusted gradation value of the black K is maintained at zero. Since the adjusted CMY tone values of the two achromatic representative values G1 and G2 used for the interpolation are determined according to the result of the colorimetry, the adjusted tone values between the CMY are adjusted. Can be different. As a result, the adjusted gradation values of CMY calculated by interpolation may be different from each other. In the example of FIG. 4B, the order of the gradation values is Y, M, and C in descending order.

  The second range R2 is a color range on the low brightness side from the low brightness representative value Gb. When the target gray value Gx is located within the second range R2, the two achromatic representative values G1 and G2 sandwiching the target gray value Gx are selected from within the second range R2. It is not located between the achromatic representative values G1 and G2. Therefore, the adjusted gradation value of CMYK corresponding to the target gray value Gx in the second range R2 is calculated in S340. As described above, the second range R2 is a color range on the lower brightness side than the reference value Gk. Since the two achromatic representative values G1 and G2 used for the interpolation are selected from the second range R2, each of the CMYK adjusted gradation values of the two achromatic representative values G1 and G2 is , Greater than zero. As a result, the adjusted gradation values of CMYK calculated by interpolation are all larger than zero. Further, similarly to the adjusted gradation values of CMY in the first range R1, the adjusted gradation values may be different between CMY in the second range R2.

  When the reference value Gk is located between the two achromatic representative values G1 and G2 (FIG. 6: S330: Yes), the two achromatic representative values G1 and G2 are the same as the representative values Gw and Gb. Is the same. In this case, in S350, the processor 110 satisfies the condition that the reference value Gk is the same as the target gray value Gx or that the reference value Gk is closer to the black vertex Vk than the target gray value Gx (that is, Gx ≦ Gk). It is determined whether or not. When this condition is satisfied (S350: Yes), in S360, the processor 110 determines whether the first achromatic color representative value G1 (that is, the high lightness representative value Gw) is on the high lightness side (that is, the white vertex Vw side). The achromatic color representative value Gs, which is the next patch representative value, is specified. Then, the processor 110 calculates the adjusted color values of CMYK corresponding to the target gray value Gx as the adjusted color values of CMYK of the high brightness representative value Gw and the adjusted color values of CMYK of the achromatic color representative value Gs. Is calculated by extrapolation using Then, the processor 110 proceeds to S380.

  The third range R3 in FIG. 4B is a color range from the high brightness representative value Gw to the reference colorimetric value Gk. When the target gray value Gx is located within the third range R3, the achromatic representative values G1 and G2 are the representative values Gw and Gb, respectively. Therefore, the reference value Gk is the two achromatic representative values G1 and G2. (That is, between the representative values Gw and Gb) (S330: Yes). Further, the target gray value Gx is equal to or smaller than the reference value Gk (S350: Yes). Therefore, the adjusted gradation value of CMYK corresponding to the target gray value Gx in the third range R3 is calculated in S360. As described above, the two representative values Gs and Gw used for the extrapolation are representative values on the higher lightness side than the reference value Gk, and therefore, the adjusted values of the black K of these representative values Gs and Gw have been adjusted. The gradation value is zero. As a result, the adjusted gradation value of black K calculated by extrapolation is also zero. That is, within the third range R3, the adjusted gradation value of the black K is maintained at zero. Further, similarly to the adjusted gradation values of CMY in the first range R1, the adjusted gradation values may be different between CMY in the third range R3.

  When the determination result of S330 in FIG. 6 is “Yes” and the target gray value Gx is positioned closer to the black vertex Vk than the reference value Gk (S350: No), the two achromatic representative values G1 and G2 are , Gb and Gb. Then, in S370, the processor 110 calculates the CMYK adjusted colorimetric value of the reference value Gk instead of the first achromatic color representative value G1, and the CMYK of the second achromatic color representative value G2 (that is, the low lightness representative value Gb). By interpolating the adjusted colorimetric values with the adjusted colorimetric values, the CMYK adjusted colorimetric values corresponding to the target gray value Gx are calculated. Then, the processor 110 proceeds to S380.

  As the CMYK adjusted colorimetric value of the reference value Gk, the CMYK colorimetric value calculated in S360 when the target gray value Gx is the same as the reference value Gk can be used. If there is no achromatic grid value corresponding to the reference value Gk, the processor 110 uses the CMYK adjusted colorimetric values of the reference value Gk for calculation according to the calculation method of 360, and uses the CMYK of the reference value Gk. May be calculated.

  The fourth range R4 in FIG. 4B is a color range from the reference value Gk to the low brightness representative value Gb. When the target gray value Gx is located within the fourth range R4, the achromatic representative values G1 and G2 are the representative values Gw and Gb, respectively. Therefore, the reference value Gk is the two achromatic representative values G1 and G2. (That is, between the representative values Gw and Gb) (S330: Yes). Further, the target gray value Gx is larger than the reference value Gk (S350: No). Therefore, the adjusted CMYK gradation value corresponding to the target gray value Gx in the fourth range R4 is calculated in S370. As described above, the low-brightness representative value Gb used for interpolation is a representative value on the lower-brightness side than the reference value Gk, so that the adjusted gradation values of CMYK of the low-brightness representative value Gb are all zero. Greater than. As a result, the adjusted gradation values of CMYK calculated by interpolation are all larger than zero. Further, similarly to the adjusted gradation values of CMY in the first range R1, the adjusted gradation values may be different between CMY in the fourth range R4.

  In S380 of FIG. 6, the processor 110 determines whether or not processing of all achromatic grid values has been completed. If unprocessed achromatic color grid values remain (S380: No), the processor 110 proceeds to S323 and executes processing of the unprocessed achromatic color grid values. If the processing of all the achromatic grid values is completed (S380: Yes), the processor 110 ends the processing of FIG. 6, that is, the processing of S250 of FIG. Then, the processor 110 ends the process of FIG. 5, that is, the process of S120 of FIG.

  In S130 of FIG. 2, the processor 110 creates a gray-adjusted lookup table. In the gray-adjusted lookup table, the adjusted CMYK colorimetric values calculated in FIGS. 5 and 6 are associated with the RGB grid values on the achromatic line AL. For the RGB grid values located away from the achromatic line AL, the processor 110 determines the CMYK colorimetric values according to a predetermined method. Various methods can be adopted as a method for determining the CMYK color values. In the present embodiment, the processor 110 determines the CMYK color specification values so that the color range (also referred to as gamut) that can be expressed by CMYK is the largest.

  FIG. 7 is an explanatory diagram of CMYK color values corresponding to grid values separated from the achromatic line AL. FIG. 7A shows the red area RA described in FIG. The first line RL1 and the second line RL2 forming the edge of the red area RA are lines on the outer shell of the color solid CC (FIG. 3). FIG. 7B is a graph showing the relationship between the color values on the outer lines RL1 and RL2 and the CMYK gradation values. The horizontal axis indicates positions on the lines RL1 and RL2, and the vertical axis indicates CMYK gradation values.

  In this embodiment, the CMYK gradation values corresponding to the grid values on the outer shell of the color solid CC are determined in advance. For example, as shown in FIG. 7B, with respect to the red vertex Vr, the grayscale value of yellow Y and the grayscale value of magenta M are determined to be the maximum values so as to reproduce the most saturated red color. , The tone value of cyan C and the tone value of black K are determined to be zero. The maximum value may be the maximum value in a range that the gradation value can take (here, 255, which is the maximum value in the range from zero to 255). Instead, a maximum value within a range that satisfies the condition for defining the upper limit value of the color material amount per unit area on the print medium may be adopted.

  The first line RL1 from the white vertex Vw to the red vertex Vr is as follows. From the white vertex Vw to the red vertex Vr, the grayscale value of the yellow Y and the grayscale value of the magenta M are changed from the grayscale value (here, zero) at the white vertex Vw to the grayscale value at the red vertex Vr. It gradually increases until. The cyan C tone value and the black K tone value are maintained at zero.

  The second line RL2 from the red vertex Vr to the black vertex Vk is as follows. A reference grid Gp is previously arranged between the red vertex Vr and the black vertex Vk on the second line RL2. Between the red vertex Vr and the reference grid Gp, the tone value of cyan C gradually increases from zero from the red vertex Vr toward the reference grid Gp. The gradation value of yellow Y and the gradation value of magenta M are maintained without being changed. The gradation value of black K is maintained at zero.

  Between the reference grid Gp and the black vertex Vk, the tone value of black K gradually increases from zero from the reference grid Gp toward the black vertex Vk. The gradation value of yellow Y and the gradation value of magenta M gradually decrease from the reference grid Gp toward the black vertex Vk. The gradation value of cyan C gradually increases from the reference grid Gp toward the black vertex Vk, and gradually decreases. Although not shown in FIG. 7, the adjusted vertex value of CMYK described in FIG. 4B is associated with the black vertex Vk. In at least a part of the color range including the black vertex Vk on the second line RL2 (for example, the color range from the reference grid Gp to the black vertex Vk), each gradation value of CMYK is not a predetermined value. , May gradually change toward each adjusted gradation value of CMYK at the black vertex Vk.

  Regarding the grid points of the inner area RAi inside the edges of the red area RA (that is, the lines AL, RL1, and RL2) shown in FIG. The CMYK colorimetric values are calculated by interpolating the respective CMYK colorimetric values of a plurality of grid points.

  As described above, the processor 110 calculates the CMYK colorimetric values of each of the plurality of grid points in the red area RA. Similarly, the CMYK color values are calculated for the grid values of other hues. That is, the CMYK color values corresponding to the grid values on the outer shell of the color solid CC are determined in advance so that the gamut is maximized. The CMYK color values corresponding to the grid values inside the outer shell are the adjusted CMYK color values of the grid values on the achromatic line AL and the CMYK color values of the same hue grid value on the outer shell. It is calculated by interpolating the values Thus, the gray-adjusted lookup table is completed.

  In S140 of FIG. 2, the processor 110 creates a final look-up table by adjusting the color values of CMYK of a specific chromatic color. For example, the processor 110 changes the CMYK color values associated with the grid value specified by the user in the gray-adjusted lookup table in accordance with the user's instruction. For example, the user can change the CMYK color values corresponding to the RGB grid values representing blue to CMYK color values suitable for an image representing the sea. The user inputs, for example, information for specifying a grid value to be changed and CMYK color values after the change through the operation unit 150. Here, the processor 110 may display the color represented by the input color specification value on the display unit 140. Note that S140 may be omitted.

  As described above, the calibration data and the look-up table are created. The created calibration data and the look-up table are used for a printing process using the printer 210. For example, when printing an image using image data represented in the RGB color space, a lookup table is used to convert RGB color values into CMYK color values. The CMYK color values are converted into CMYK corrected color values using the calibration data. Then, print data is generated by halftone processing using the CMYK corrected color values. Such calibration data and the look-up table may be incorporated in a printer driver for controlling the printer 210. Note that the calibration data and the look-up table are prepared for each model of the printer 210. Alternatively, calibration data and a look-up table may be prepared for each printer 210.

  As described above, in the present embodiment, as described with reference to S360 in FIG. 6 and the third range R3 in FIG. 4B, the processor 110 determines the reference colorimetric value Gk and the high brightness representative value on the achromatic line AL. The CMYK color value corresponding to the RGB grid value between the value Gw and the CMYK color value corresponding to the RGB value is associated with the high brightness representative value Gw without using the CMYK color value associated with the low brightness representative value Gb. It is calculated using CMYK color values. As described above, the tone value of black K associated with the low brightness representative value Gb on the lower brightness side than the reference value Gk can exceed zero, but is not used for calculating the CMYK color specification values. . Further, the gradation value of black K associated with the high brightness representative value Gw on the higher brightness side than the reference value Gk is zero, and is used for calculating the CMYK color specification values. Therefore, it is possible to prevent the grayscale value of the black K from unintentionally becoming larger than zero between the reference color value Gk and the high brightness representative value Gw on the achromatic line AL.

  Further, as described in S370 of FIG. 6 and the fourth range R4 of FIG. 4B, the processor 110 converts the RGB grid between the reference value Gk and the low brightness representative value Gb on the achromatic line AL. The CMYK color value corresponding to the value is calculated using the CMKY color value associated with the low lightness representative value Gb. Since the low lightness representative value Gb close to the grid value is used as described above, an appropriate CMYK colorimetric value can be calculated. For example, in the fourth range R4, the gradation value of black K is determined to be a value larger than zero.

  As described above, when the achromatic line AL is traced from the white vertex Vw to the black vertex Vk, the position where the gradation value of the black K changes from zero to a value larger than zero is maintained without changing from the reference value Gk. can do. Further, in this embodiment, the reference color value Gk is not included in the patch representative values described with reference to FIGS. Therefore, it is possible to suppress a change in the reference color value Gk without printing a patch for the reference color value Gk.

  Further, as described with reference to S340 in FIG. 6 and the first range R1 and the second range R2 in FIG. 4B, the processor 110 sets a higher lightness side than the high lightness representative value Gw on the achromatic line AL. A CMYK colorimetric value corresponding to the grid value and a CMYK colorimetric value corresponding to a grid value on the achromatic color line AL corresponding to a grid value lower than the low lightness representative value Gb are adjacent to each other on the achromatic color line AL. It is calculated by interpolation using two achromatic representative values G1 and G2 sandwiching the values. As described above, since the two achromatic representative values G1 and G2 which are close to the grid value and sandwich the grid value are used for interpolation, an appropriate CMYK colorimetric value can be calculated.

  Further, as described with reference to S360 in FIG. 6 and the third range R3 in FIG. 4B, the processor 110 determines whether the grid between the reference colorimetric value Gk and the high brightness representative value Gw on the achromatic line AL is high. The CMYK color value corresponding to the CMYK color value is represented by the CMYK color value associated with the high lightness representative value Gw and the CMYK color value adjacent to the high lightness side of the high lightness representative value Gw. It is calculated by extrapolation using color specification values. As described above, since the two achromatic color representative values Gw and Gs close to the grid value are used for extrapolation, an appropriate CMYK colorimetric value can be calculated.

  Further, the processor 110 generates information indicating the correspondence between the achromatic representative value and the adjusted CMYK colorimetric values by executing S210 to S240 in FIG. 5 (also referred to as color correspondence information). Any format can be adopted as the data format of the color correspondence information (for example, a lookup table). If the determination result in S240 is Yes, the processor 110 temporarily stores the generated color correspondence information in a storage device (for example, the nonvolatile storage device 130 or the volatile storage device 120). Then, in S250, that is, in S340, S360, and S370 in FIG. 6, the processor 110 refers to the color correspondence information in the storage device and uses the adjusted colorimetric value associated with the achromatic color representative value to generate the CMYK Calculate the color specification value. Here, as described in S230 of FIG. 5, the adjusted colorimetric value is determined based on the target color value associated with the RGB achromatic color representative value. Therefore, it can be said that the adjusted colorimetric value is associated with the target color value. As described above, in S340, S360, and S370 in FIG. 6, since the adjusted colorimetric value associated with the target color value is used to calculate the CMYK colorimetric value, the CMYK colorimetric value suitable for the target color value is used. Can be calculated.

  Further, as shown in FIGS. 4A and 4B, a distance between two achromatic representative values (specifically, two patch representative values) adjacent on the achromatic line AL. Differs depending on the position on the achromatic line AL. For example, the distance is 16 in a range from zero to 48, which is a part of the range including the white vertex Vw (referred to as a high brightness range). The distance is 15 in a range from 240 to 255, which is a part of the range including the black vertex Vk (referred to as a low brightness range). In the remaining range from 48 to 240 (called the middle range), the distance is 32. Thus, the maximum distance is 32. The two achromatic representative values having the largest distance are two achromatic representative values located inside the achromatic representative values Vw and Vk at both ends on the achromatic line AL. In other words, the distance between two adjacent achromatic color representative values belonging to the intermediate range is the distance between two adjacent achromatic color representative values belonging to the high brightness range, and the distance between two adjacent achromatic color representative values belonging to the low brightness range. And the distance between the achromatic representative values. Therefore, in a part of the color range including the white vertex Vw representing white, which is the color with the highest brightness, and the part of the color range including the black vertex Vk representing black, which is the color with the lowest brightness, an achromatic representative color is used. It is possible to suppress the value density from becoming coarse. As a result, in some color ranges including white and some color ranges including black, it is possible to suppress the calculation of CMYK color values that represent unnatural colors. For example, it is possible to prevent a color that should be achromatic from being printed in a chromatic color. The high lightness range, the low lightness range, and the intermediate range may be different from the above ranges.

B. Second embodiment:
FIG. 8 is a flowchart illustrating an example of the procedure of the printing process. In the second embodiment, in the color conversion process in the printing process, the calculation of the color specification value similar to the process described with reference to FIG. 6 is performed. Hereinafter, the description will be given assuming that the processor 110 operating according to the third program for printing 136 (FIG. 1) executes the processing of FIG. It is assumed that the calibration data generated in S100 of FIG. 2 and the look-up table generated in S110 to S140 are incorporated in the third program 136. In this embodiment, it can be said that the lookup table is color correspondence information that associates the CMYK color values with each of the plurality of RGB grid values. The RGB grid values are representative color values in which the CMYK color values are associated with the lookup table among various color values in the RGB color space. Therefore, in the present embodiment, it can be said that the RGB grid values are the representative color values (or simply, representative values) associated with the CMYK color values.

  In S10, the processor 110 acquires a print instruction from the user via the operation unit 150. The print instruction includes an instruction to specify target image data to be printed. The processor 110 acquires target image data specified by the user. For example, target image data is acquired from a storage device (for example, the nonvolatile storage device 130). The target image data is, for example, image data described in a page description language or image data compressed in a JPEG format.

  In S20, the processor 110 performs a rasterizing process on the acquired target image data to generate bitmap data for a printing process representing a target image including a plurality of pixels. In the present embodiment, the bitmap data is RGB image data representing a color for each pixel by RGB gradation values. If the target image data is bitmap data, the processor 110 may execute a process of converting the resolution (that is, the pixel density) of the bitmap data into a resolution for printing.

  In S30, the processor 110 performs a color conversion process on the RGB image data to generate image data corresponding to a type of a color material usable for printing. In this embodiment, CMYK image data is generated. The color conversion process is performed using a look-up table that determines the correspondence between RGB tone values and CMYK tone values (details will be described later).

  In S35, the processor 110 converts the CMYK gradation values into corrected gradation values using the calibration data.

  In S40, the processor 110 performs halftone processing on the corrected gradation values of CMYK to generate dot data representing the dot formation state for each pixel and for each type of ink. In the present embodiment, the halftone process is executed using an error diffusion process using an error matrix. Instead, halftone processing using a dither matrix may be employed.

  In S50, the processor 110 generates print data using the dot data. The print data is data represented in a data format that can be interpreted by the printer 210. The processor 110, for example, arranges dot data in the order used for printing, and adds various printer control codes and data identification codes to generate print data.

  In S60, the processor 110 supplies the generated print data to the printer 210. In S70, the printer 210 prints an image according to the received print data. Thus, the printing process in FIG. 8 ends.

  FIG. 9 is a flowchart illustrating an example of the procedure of the color conversion process. FIG. 9 shows a process of converting the color specification value of one pixel. In the present embodiment, the color conversion processing of FIG. 9 is performed for each pixel. In S300, the processor 110 acquires the RGB color values to be processed (that is, the first type color values). In S303, the processor 110 determines whether the first type color specification value represents an achromatic color. In this embodiment, when R = G = B, it is determined that the first type color specification value represents an achromatic color. Hereinafter, the first type color value to be processed is also referred to as a target color value.

  If the target colorimetric value does not represent an achromatic color (S303: No), in S306, the processor 110 forms the smallest triangular pyramid including the target colorimetric value among the plurality of grid values included in the lookup table. 4 grid values to be selected. In S310, the processor 110 calculates the CMYK color values corresponding to the target color values by interpolating the four CMYK color values corresponding to the selected four grid values. Then, the processor 110 ends the processing in FIG.

  If the target color value indicates an achromatic color (S303: Yes), in S320, the processor 110 specifies the reference value Gk. As described with reference to FIGS. 4A and 4B, when the gray value GV is increased from the white vertex Vw, the reference value Gk is changed from zero to a value larger than zero. The changing color values are shown. The processor 110 specifies such a reference value Gk with reference to data stored in the nonvolatile storage device 130 in advance. For example, data representing the reference value Gk may be incorporated in the third program 136 for printing in advance. Note that the reference value Gk specified in S320 may be different from the reference value Gk used in creating the lookup table. For example, in S320, the processor 110 may adopt a value specified by the user as the reference value Gk. The user may specify the reference value Gk in consideration of the graininess and the like.

  Subsequent steps S326a, S330a, S340a, S350a, S360a, and S370a are the same as S326, S330, S340, S350, S360, and S370 of FIG. 6 with the following modifications. That is, in the process of FIG. 9, the gray value GV representing the target color value is used as the target gray value Gx. Further, as the achromatic color representative value used for calculation of the color specification value such as interpolation and extrapolation, not only the patch representative value but also all grid values on the achromatic color line AL included in the lookup table are used. Except for these modifications, S326a, S330a, S340a, S350a, S360a, and S370a in FIG. 9 are the same as S326, S330, S340, S350, S360, and S370 in FIG. 6, respectively. Accordingly, the CMYK color values calculated by the color conversion process of FIG. 9, particularly the CMYK color values associated with the target color values on the achromatic line AL, are the CMYK color values described with reference to FIG. Is the same as the color specification value.

  In this embodiment, all grid values on the achromatic line AL are used as achromatic representative values. Therefore, the representative value Gw adjacent to the reference value Gk on the high lightness side (that is, the white vertex Vw side) may be an achromatic representative value different from the representative value Gw in FIG. 4B. Similarly, the representative value Gb adjacent to the low brightness side of the reference value Gk (that is, the black vertex Vk side) may be a representative value different from the low brightness representative value Gb of FIG.

  Also in the present embodiment, similarly to the third range R3 in FIG. 4B, the processor 110 sets the target colorimetric value between the reference colorimetric value Gk and the high lightness representative value Gw on the achromatic color line AL. The corresponding CMYK colorimetric value is calculated using the CMYK colorimetric value associated with the high lightness representative value Gw, without using the CMYK colorimetric value associated with the low lightness representative value Gb. Therefore, it is possible to prevent the grayscale value of the black K from unintentionally becoming larger than zero between the reference color value Gk and the high brightness representative value Gw on the achromatic line AL.

  Further, similarly to the fourth range R4 in FIG. 4B, the processor 110 determines the CMYK color specification corresponding to the target color value between the reference value Gk and the low brightness representative value Gb on the achromatic line AL. The value is calculated using the CMKY color specification value associated with the low brightness representative value Gb. As described above, since the low brightness representative value Gb close to the target color value is used, an appropriate CMYK color value can be calculated.

  As described above, when the achromatic line AL is traced from the white vertex Vw to the black vertex Vk, the position where the gradation value of the black K changes from zero to a value larger than zero is maintained without changing from the reference value Gk. can do.

  Further, similarly to the first range R1 and the second range R2 of FIG. 4, the processor 110 outputs the CMYK colorimetric values corresponding to the target colorimetric value on the higher lightness side than the high lightness representative value Gw on the achromatic line AL. And the CMYK color values corresponding to the target color value on the achromatic line AL corresponding to the target color value lower than the low lightness representative value Gb on the achromatic line AL, and sandwich the target color value between them. It is calculated by interpolation using two achromatic representative values G1 and G2. Therefore, the CMYK color values suitable for the target color value can be calculated.

  Further, similarly to the third range R3 in FIG. 4B, the processor 110 sets the target color value between the reference color value Gk and the high lightness representative value Gw on the achromatic line AL as the target color value. The corresponding CMYK color values are represented by the CMYK color values associated with the high-brightness representative value Gw and the CMYK color values associated with the achromatic representative value Gs adjacent to the high-brightness representative value Gw on the high-brightness side. The value is calculated by extrapolation using Therefore, the CMYK color values suitable for the target color value can be calculated.

  In the lookup table, the densities of the plurality of grid values may be different depending on the colors. For example, like a patch representative value indicated by a black point in FIG. 4B, in a partial color range including the white vertex Vw and a partial color range including the black vertex Vk on the achromatic line AL, The grid value density may be higher than the remaining range of the coloring line AL. That is, when focusing on the distance between two adjacent grid values, the two grid values having the largest distance are located inside the achromatic representative values Vw and Vk at both ends on the achromatic line AL. It may be two grid values located. According to this, in some color ranges including white and some color ranges including black, it is possible to suppress calculation of CMYK color values that represent unnatural colors.

C. Modification:
(1) As a procedure of a process of calculating a color specification value represented by a plurality of color components corresponding to a type of a color material, various other procedures can be adopted instead of the procedures of FIGS. is there. For example, in the first range R1 and the second range R2 of FIG. 4B, the processor 110 includes L (L is 2 or more) including two achromatic representative values G1 and G2 sandwiching the target gray value Gx. The CMYK color values corresponding to the gray value of interest Gx may be calculated by interpolation using L CMYK color values of the achromatic color representative value of (integer). As the L achromatic representative values, for example, L achromatic representative values closest to the target gray value Gx may be employed.

  In addition, in the third range R3 of FIG. 4B, the processor 110 does not use the CMYK color values corresponding to the low brightness representative value Gb, but uses the M (from the high brightness representative value Gw to the white vertex Vw side). The CMYK color values corresponding to the target gray value Gx may be calculated by extrapolation using the M CMYK color values of the achromatic representative value (M is an integer of 2 or more).

  Further, in the fourth range R4 of FIG. 4B, the processor 110 uses P (P: P) arranged from the low brightness representative value Gb to the black vertex Vk side without using the CMYK color value corresponding to the reference value Gk. The CMYK color value corresponding to the target gray value Gx may be calculated by extrapolation using the P CMYK color values of the achromatic representative value (an integer of 2 or more).

(2) In the embodiment shown in FIGS. 4A and 4B, the arrangement of a plurality of patch representative values may be different from the arrangement of the illustrated black dots. For example, a plurality of patch representative values may be evenly arranged between the white vertex Vw and the black vertex Vk.

(3) A plurality of achromatic representative values, such as a plurality of patch representative values indicated by black dots in FIGS. 4A and 4B, need only be located approximately on the achromatic line AL, It may be slightly away from the line AL. For example, even if the achromatic color representative value is far from the achromatic color line AL, when the color printed in accordance with the achromatic color representative value is visually observed, it can be determined that the color is an achromatic color. In other words, it can be said that the achromatic representative value is approximately located on the achromatic line AL.

(4) As the process of creating the lookup table, various other processes can be adopted instead of the process shown in FIG. For example, S100 and the calibration data may be omitted. Further, S140 may be omitted.

(5) As the correspondence between the RGB color values and the CMYK color values, various other correspondences are used instead of the correspondences shown in FIGS. 4A, 4B, and 7. Can be adopted. For example, in the embodiment of FIGS. 4A and 4B, the CMY tone values may continue to increase without decreasing with increasing gray value GV. Further, in the embodiment of FIG. 7, the gradation value of yellow Y and the gradation value of magenta M may gradually decrease from the red vertex Vr toward the reference grid Gp.

(6) The total number of patches associated with one noted representative value is not limited to 125 and 625, and any other number can be adopted (for example, any number of 2 or more). For example, the tone value of a color component having an unadjusted tone value greater than zero may be changed in three stages. For example, when K = 0 and CMY> 0, the three tone values of CMY change in three steps, and the total number of patches is 3 × 3 × 3 = 27. When all of CMYK are larger than zero, the four gradation values of CMYK change in three steps, and the total number of patches is 3 × 3 × 3 × 3 = 81.

(7) As the printing process, various other processes can be adopted instead of the process shown in FIG. For example, S35 may be omitted. Further, as the lookup table used in S30, an arbitrary table can be adopted instead of the table created in the procedure of FIG. For example, a look-up table created without using colorimetric values may be used.

(8) Instead of CMYK, various other types of color materials that can be used for printing can be adopted. For example, there are five available colorants, CMYK and light cyan LC, which is thinner than cyan C. Generally, a plurality of types of color materials including an achromatic color material may be employed. Here, in addition to the achromatic color material, it is preferable to be able to use a plurality of types of chromatic color materials (for example, three types of CMY) capable of expressing an achromatic color by mixing colors. According to this, a bright achromatic color can be printed by mixing a plurality of types of chromatic color materials without using an achromatic color material such as black K, so that graininess can be improved.

(9) Color correspondence information (for example, the correspondence between the achromatic color representative value specified in S210 to S240 in FIG. 5 and the adjusted CMYK colorimetric values, the lookup table used in the printing process in FIG. 8, and the like) For the combination of the color spaces associated with the above, instead of the combination of the RGB color space and the CMYK color space, any other combination of color spaces can be adopted. For example, the color correspondence information includes a plurality of representative color values in a YCbCr color space and a color space represented by a plurality of color components corresponding to a plurality of available color materials (for example, a CMYK color space, A plurality of color values in the CMYKLc color space (Lc is the color component of light cyan LC) may be associated.

(10) A calculation device that calculates tone values of a plurality of color components corresponding to a plurality of types of color materials using a plurality of achromatic color representative values is a device of a type different from a personal computer (for example, a digital camera, Scanner, smartphone). Further, the calculation device may be a part of the printing device. In addition, a plurality of devices (for example, computers) that can communicate with each other via a network share a part of the function of the gradation value calculation processing by the calculation device, and provide the calculation processing function as a whole. (A system including these devices corresponds to a calculating device).

  In each of the above embodiments, a part of the configuration realized by hardware may be replaced by software, and conversely, a part or all of the configuration realized by software may be replaced by hardware. Is also good. For example, the function of executing the calculation processing of FIG. 6 may be realized by a dedicated hardware circuit.

  When part or all of the functions of the present invention are implemented by a computer program, the program is provided in a form stored in a computer-readable recording medium (for example, a non-temporary recording medium). be able to. The program can be used in a state stored in the same or different recording medium (computer-readable recording medium) at the time of provision. The “computer-readable recording medium” is not limited to a portable recording medium such as a memory card or a CD-ROM, but is connected to an internal storage device in the computer such as various ROMs or a computer such as a hard disk drive. External storage may also be included.

  As described above, the present invention has been described based on the examples and the modified examples. However, the above-described embodiments are for facilitating understanding of the present invention, and do not limit the present invention. The present invention can be modified and improved without departing from the spirit and scope of the claims, and the present invention includes equivalents thereof.

100 data processing device, 110 processor, 120 volatile storage device, 130 nonvolatile storage device, 132 first program, 134 second program, 136. ..3rd program, 140 ... display unit, 150 ... operation unit, 190 ... interface, 200 ... colorimeter, 210 ... printer, T ... triangle, G1 ... First achromatic representative value, G2 ... second achromatic representative value, R1 ... first range, R2 ... second range, R3 ... third range, R4 ... fourth range, RA: red region, CC: color solid, AL: achromatic line, GV: gray value, CV: colorimetric value, Ca, Ma, Ya, Ka: correction floor Tone value, Gb: low brightness representative value, Cb, Mb, Yb, Kb: corrected tone value, Vr: red vertex, Vg: green vertex, Vbl: blue vertex, Vc ... Cyan vertex, Vm ... Magenta vertex, Vy ... Yellow vertex, Vk ... Black vertex Vw: white vertex, Gk: reference value (reference color value), Gp: reference grid, Gx: target gray value, RL1: first line, RL2 ... second line , LUT ... look-up table, RAi ... inner area, CVx ... target color value

Claims (6)

A second type of color value, which is a color value in the second color space, corresponding to a first type of color value, which is a color value in the first color space, is calculated using the color correspondence information. In the calculation device, the color correspondence information includes a plurality of first type representative color values in the first color space, a plurality of second type representative color values in the second color space, The calculation device is information that associates
The second type color value is represented by a plurality of color components corresponding to the plurality of types of color materials including an achromatic color material and a plurality of types of color materials used for printing,
The plurality of first-type representative color values include a plurality of achromatic representative values on an achromatic line connecting white and black in the first color space,
The plurality of achromatic representative values are two achromatic representative values that are adjacent to each other on the achromatic line, and are the achromatic representative values on the high lightness side of the two achromatic representative values. A high-brightness representative value, and a low-brightness representative value that is an achromatic representative value on the low-brightness side of the two achromatic color representative values ;
The high brightness representative value and the low brightness representative value sandwich a reference color value on the achromatic color line,
The reference color value is the blackest among the first type color values on the achromatic line associated with the second type color value in which the value of the color component of the achromatic color material is zero. And a color specification value different from any of the plurality of achromatic representative values,
The calculation device,
A second type color value corresponding to a first type color value between the reference color value and the high lightness representative value on the achromatic line is a second color value corresponding to the low lightness representative value. A first calculation unit that calculates using a second type color value associated with the high brightness representative value without using a type color value;
A second type color value corresponding to a first type color value between the reference color value and the low lightness representative value on the achromatic line is a second color value associated with the low lightness representative value. A second calculator for calculating using the seed color value,
A calculation device comprising:
The calculation device according to claim 1,
On the achromatic color line, a second type color specification value corresponding to a first type color value higher than the high lightness representative value, and a first type color value lower than the low lightness representative value. A third type color value corresponding to the color value is calculated by interpolation using two achromatic color representative values that are adjacent to each other on the achromatic color line and sandwich the first type color value. A calculation device comprising a calculation unit. The calculation device according to claim 1 or 2,
The first calculation unit associates the second type color specification value associated with the high brightness representative value with an achromatic color representative value adjacent to the high brightness side of the high brightness representative value on the achromatic color line. A calculation device that calculates the second type color value by extrapolation using the obtained second type color value. The calculation device according to claim 1, wherein:
The second type representative color value associated with the first type representative color value by the color correspondence information is a table associated with a target color value associated with the first type representative color value. A calculation device that is a color value. The calculation device according to claim 1, wherein:
The plurality of achromatic color representative values arranged along the achromatic line are a high brightness range including an achromatic color indicating white, a low brightness range including an achromatic color indicating black, the high brightness range and the low brightness range. Belongs to any of the intermediate range between
The distance between the achromatic representative values belonging to the intermediate range is larger than any of the distance between the achromatic representative values belonging to the high brightness range and the distance between the achromatic representative values belonging to the low brightness range. , Calculation device. A second type of color value, which is a color value in the second color space, corresponding to a first type of color value, which is a color value in the first color space, is calculated using the color correspondence information. Computer-readable storage medium, wherein the color correspondence information includes a plurality of first type representative color values in the first color space and a plurality of second type representative color values in the second color space. And the computer program, which is information for associating,
The second type color value is represented by a plurality of color components corresponding to the plurality of types of color materials including an achromatic color material and a plurality of types of color materials used for printing,
The plurality of first-type representative color values include a plurality of achromatic representative values on an achromatic line connecting white and black in the first color space,
The plurality of achromatic representative values are two achromatic representative values that are adjacent to each other on the achromatic line, and are the achromatic representative values on the high lightness side of the two achromatic representative values. A high-brightness representative value, and a low-brightness representative value that is an achromatic representative value on the low-brightness side of the two achromatic color representative values ;
The high brightness representative value and the low brightness representative value sandwich a reference color value on the achromatic color line,
The reference color value is the blackest among the first type color values on the achromatic line associated with the second type color value in which the value of the color component of the achromatic color material is zero. And a color specification value different from any of the plurality of achromatic representative values,
The computer program comprises:
A second type color value corresponding to a first type color value between the reference color value on the achromatic color line and the high lightness representative value is a second color value corresponding to the low lightness representative value. A first calculation function for calculating using the second type color value associated with the high brightness representative value without using the type color value;
A second type color value corresponding to a first type color value between the reference color value on the achromatic color line and the low lightness representative value is a second type color value associated with the low lightness representative value. A second calculation function for calculating using the seed color value;
A computer program that causes a computer to realize

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