Color processing device that converts combination of colors into larger number of combination of colors, color processing method, and storage medium

1. A color processing device, comprising:

a converter that converts a combination of values of N−1 colors, which are obtained by eliminating a specific color included in N colors from an input color signal expressing a color by a combination of values of the N colors, into a corresponding combination of values of M−1 colors, N being 4 or larger, M being larger than N; and

an output unit that, if a total value of the values of the M−1 colors after the conversion by the converter and a value of the specific color included in the input color signal exceeds a predetermined limit value, changes a value of at least one of M colors, which are obtained by adding the specific color to the M−1 colors, such that the total value becomes the limit value or smaller, and outputs values of the M colors as an output color signal,

wherein the M colors of the output color signal includes a basic color and a non-basic color, and

wherein, when a total value of the values of the M colors exceeds the limit value, the output unit judges whether or not a total value of values of remaining colors exceeds the limit value, the remaining colors being obtained by eliminating the non-basic color from the M colors, changes a value of the non-basic color such that the total value of the values of the M colors becomes the limit value or smaller if the total value of the values of the remaining colors is the limit value or smaller, and changes the value of the non-basic color into a predetermined minimum value and changes a value of the basic color such that the total value of the values of the M colors becomes the limit value or smaller if the total value of the values of the remaining colors exceeds the limit value.

2. The color processing device according to claim 1 ,

wherein the N colors of the input color signal and the M colors of the output color signal each include black, and

wherein the converter converts the combination of the values of the N−1 colors, which are obtained by eliminating the black serving as the specific color from the N colors, into the corresponding combination of the values of the M−1 colors, which are obtained by eliminating the black serving as the specific color from the M colors.

3. The color processing device according to claim 1 , wherein the converter converts the combination of the values of the N−1 colors into the corresponding combination of the values of the M−1 colors within a range satisfying that a total value of the values of the M−1 colors is the limit value or smaller, M being larger than N.

4. The color processing device according to claim 1 ,

wherein the basic color is at least three colors capable of being reproduced even if the non-basic color is not used, and

wherein the non-basic color is at least one of a light color with a density lower than a density of the basic color and a special color having a hue different from a hue of the basic color.

5. The color processing device according to claim 1 ,

wherein the M−1 colors include a basic color and a light color with a density lower than a density of the basic color, and

wherein the converter converts the combination of the values of the N−1 colors into the corresponding combination of the values of the M−1 colors by determining a maximum light-color amount, which is a maximum value of the light color, within a range of a predetermined color difference from the combination of the values of the N−1 colors of the input color signal, obtaining a value of the light color included in the M−1 colors in accordance with the determined maximum light-color amount and an under color removal ratio, and obtaining a value of the basic color included in the M−1 colors from the obtained value of the light color and the combination of the values of the N−1 colors of the input color signal.

6. The color processing device according to claim 5 , wherein the under color removal ratio is set based on a function for a value of one of the N−1 colors of the input color signal.

7. The color processing device according to claim 5 , wherein the maximum light-color amount is determined within a range satisfying that the total value of the values of the M−1 colors is the limit value or smaller.

8. The color processing device according to claim 1 ,

wherein the M−1 colors include a basic color and a light color with a density lower than a density of the basic color,

wherein the converter converts the combination of the values of the N−1 colors into the corresponding combination of the values of the M−1 colors by performing interpolation computation based on conversion data that associates a plurality of combinations of values of the N−1 colors with a plurality of corresponding combinations of values of the M−1 colors, and

wherein the conversion data is previously generated by determining a maximum light-color amount, which is a maximum value of the light color, within a range of a predetermined color difference from the combination of the values of the N−1 colors of the input color signal, obtaining a value of the light color included in the M−1 colors in accordance with the determined maximum light-color amount and an under color removal ratio, and performing processing of obtaining a value of the basic color included in the M−1 colors from the obtained value of the light color and the combination of the values of the N−1 colors of the input color signal for each of the plurality of combinations of the values of the N−1 colors.

9. The color processing device according to claim 8 , wherein the under color removal ratio is set based on a function for a value of one of the N−1 colors of the input color signal.

10. The color processing device according to claim 8 , wherein the maximum light-color amount is determined within a range satisfying that the total value of the values of the M−1 colors is the limit value or smaller.

11. The color processing device according to claim 1 , further comprising:

a color signal converter that converts a color signal that is input, into a color signal corresponding to a color reproducibility of a color reproducing device to which the output color signal is input, and

wherein the color signal after the color-signal conversion by the color signal converter is input as the input color signal to the converter.

12. A non-transitory computer readable medium storing a program causing a computer to execute a process for color processing, the process comprising:

converting a combination of values of N−1 colors, which are obtained by eliminating a specific color included in N colors from an input-color signal expressing a color by a combination of values of the N colors, into a corresponding combination of values of M−1 colors, N being equal to or larger than 4, M being larger than N; and

if a total value of the values of the M−1 colors after the conversion and a value of the specific color included in the input-color signal exceeds a predetermined limit value, changing a value of at least one of M colors, which are obtained by adding the specific color to the M−1 colors, such that the total value becomes the limit value or smaller, and outputting values of the M colors as an output color signal,

wherein the M colors of the output color signal includes a basic color and a non-basic color, and

wherein, when a total value of the values of the M colors exceeds the limit value, the process further comprises determining whether or not a total value of values of remaining colors exceeds the limit value, the remaining colors being obtained by eliminating the non-basic color from the M colors, changing a value of the non-basic color such that the total value of the values of the M colors becomes the limit value or smaller if the total value of the values of the remaining colors is the limit value or smaller, and changing the value of the non-basic color into a predetermined minimum value and changes a value of the basic color such that the total value of the values of the M colors becomes the limit value or smaller if the total value of the values of the remaining colors exceeds the limit value.

13. An image processing method comprising:

converting a combination of values of N−1 colors, which are obtained by eliminating a specific color included in N colors from an input-color signal expressing a color by a combination of values of the N colors, into a corresponding combination of values of M−1 colors, N being equal to or larger than 4, M being larger than N; and

if a total value of the values of the M−1 colors after the conversion and a value of the specific color included in the input-color signal exceeds a predetermined limit value, changing a value of at least one of M colors, which are obtained by adding the specific color to the M−1 colors, such that the total value becomes the limit value or smaller, and outputting values of the M colors as an output color signal,

wherein the M colors of the output color signal includes a basic color and a non-basic color, and

wherein, when a total value of the values of the M colors exceeds the limit value, the method further comprises determining whether or not a total value of values of remaining colors exceeds the limit value, the remaining colors being obtained by eliminating the non-basic color from the M colors, changing a value of the non-basic color such that the total value of the values of the M colors becomes the limit value or smaller if the total value of the values of the remaining colors is the limit value or smaller, and changing the value of the non-basic color into a predetermined minimum value and changes a value of the basic color such that the total value of the values of the M colors becomes the limit value or smaller if the total value of the values of the remaining colors exceeds the limit value.