Color correction parameter computation method, color correction parameter computation device, and image output system

1. A color correction parameter computation method comprising:

obtaining a plurality of first color signal values that respectively correspond to colors of a plurality of color patches and are obtained by photographing a color chart having the color patches on a surface, and a plurality of reference color signal values respectively defining the colors of the color patches;

computing, for each one of the colors of the color patches, a color difference component between a corresponding one of the first color signal values and a corresponding one of the reference color signal values;

selecting at least one color of the color patches based on comparison of magnitude of the obtained color difference components;

computing a color correction parameter using the first color signal value corresponding to the selected color and the reference color signal value that defines the selected color, the color correction parameter being a parameter that makes the color difference component between a first corrected color signal value which is obtained by correcting the first color signal value corresponding to the selected color using the color correction parameter and the reference color signal value defining the selected color smaller than the color difference component between the first color signal value corresponding to the selected color and the reference color signal value defining the selected color;

computing a measure of accuracy using the color difference component between a second corrected color signal value which is obtained by correcting a first color signal value corresponding to a color other than the selected color using the color correction parameter and the reference color signal value that defines the color other than the selected color; and

determining accuracy of correction by comparing the measure of accuracy to a predetermined accuracy criterion.

2. The color correction parameter computation method according to claim 1 ,

wherein if the accuracy is determined not to satisfy a predetermined accuracy in the determining the accuracy of correction, the method further comprising selecting a color other than the selected color based on comparison of magnitude of the color difference components between the second corrected color signal values and reference color signal values defining colors other than the selected color, and the computing a color correction parameter, the computing a measure of accuracy and the determining the accuracy of correction are executed again.

3. The color correction parameter computation method according to claim 2 ,

wherein the selecting a color other than the selected color includes selecting colors in descending order of the magnitude of the color difference components between the second corrected color signal values and reference color signal values defining colors other than the selected color.

4. The color correction parameter computation method according to claim 1 ,

wherein the obtaining a plurality of first color signal values includes obtaining the plurality of first color signal values by photographing the color chart.

5. The color correction parameter computation method according to claim 1 ,

wherein the plurality of reference color signal values are signal values obtained by measuring the colors of the plurality of color patches.

6. The color correction parameter computation method according to claim 1 ,

wherein the selecting at least one color of the color patches includes selecting colors in descending order of the magnitude of the color difference components.

7. The color correction parameter computation method according to claim 1 ,

wherein the plurality of first color signal values and the plurality of reference color signal values are coordinate values in CIE 1976 L*a*b* color space.

8. The color correction parameter computation method according to claim 1 ,

wherein the color correction parameter computed in the computing the color correction parameter is a parameter defined so that the color difference component between the first corrected color signal value and the reference color signal value defining the selected color is 0.

9. The color correction parameter computation method according to claim 1 ,

wherein the computing the measure of accuracy includes

computing, for each one of colors other than the selected color, the color difference component between a corresponding one of the second corrected color signal values and a corresponding reference color signal value that defines the color other than the selected color, and

of computing an average value of the color difference components and setting the average value as the measure of accuracy.

10. The color correction parameter computation method according to claim 1 ,

wherein the computing the measure of accuracy includes

of computing, for each one of colors other than the selected color, the color difference component between a corresponding one of the second corrected color signal values and a corresponding reference color signal value that defines the color other than the selected color,

extracting a maximum value of the color difference components, and

setting the maximum value as the measure of accuracy.

11. The color correction parameter computation method according to claim 1 ,

wherein the computing the measure of accuracy includes

computing, for each one of colors other than the selected color, the color difference component between a corresponding one of the second corrected color signal values and a corresponding reference color signal value that defines the color other than the selected color,

computing an average value of the color difference components determined,

extracting a maximum value of the color difference components determined, and

setting a weighted sum of the average value and the maximum value as the measure of accuracy.

12. A color correction parameter computation device comprising:

one or more processors; and

a memory in which a program to be executed by the one or more processors is stored,

wherein the program includes instructions for executing a process including

obtaining a plurality of first color signal values that respectively correspond to colors of a plurality of color patches and are obtained by photographing a color chart having the color patches on a surface, and a plurality of reference color signal values respectively defining the colors of the color patches,

computing, for each one of the colors of the color patches, a color difference component between a corresponding one of the first color signal values and a corresponding one of the reference color signal values,

selecting at least one color of the color patches based on comparison of magnitude of the obtained color difference components,

computing a color correction parameter using the first color signal value corresponding to the selected color and the reference color signal value that defines the selected color, the color correction parameter being a parameter that makes the color difference component between a first corrected color signal value which is obtained by correcting the first color signal value corresponding to the selected color using the color correction parameter and the reference color signal value defining the selected color smaller than the color difference component between the first color signal value corresponding to the selected color and the reference color signal value defining the selected color,

computing a measure of accuracy using the color difference component between a second corrected color signal value which is obtained by correcting a first color signal value corresponding to a color other than the selected color using the color correction parameter and the reference color signal value that defines the color other than the selected color, and

determining accuracy of correction by comparing the measure of accuracy to a predetermined accuracy criterion.

13. The color correction parameter computation device according to claim 12 ,

wherein the program further includes instructions for

if the accuracy is determined not to satisfy a predetermined accuracy in the determining the accuracy of correction, further selecting a color other than the selected color based on comparison of magnitude of the color difference components between the second corrected color signal values and reference color signal values defining colors other than the selected color, and

after executing the selecting a color other than the selected color, executing the computing the color correction parameter, computing the measure of accuracy, and determining the accuracy of correction again.

14. The color correction parameter computation device according to claim 13 ,

wherein the selecting the at least one color of the color patches includes selecting colors in descending order of the magnitude of the color difference components between the second corrected color signal values and reference color signal values defining colors other than the selected color determined.

15. The color correction parameter computation device according to claim 12 ,

wherein the selecting the at least one color of the color patches includes storing in the memory a list of a pair of the first color signal value corresponding to the selected color and the reference color signal value defining the selected color based on comparison of the magnitude of the color difference components.

16. An image output system comprising:

an image capture device;

a color correction device that receives image information obtained by the image capture device and color correction parameters computed by a color correction parameter computation device and performs color correction to the image information; and

an output device that displays or prints an output from the color correction device,

wherein the color correction parameter computation device includes

one or more processors, and

a memory in which a program to be executed by the one or more processors is stored,

wherein the program includes instructions for executing a process including

obtaining a plurality of first color signal values that respectively correspond to colors of a plurality of color patches and are obtained by photographing a color chart having the color patches on a surface using the image capture device, and a plurality of reference color signal values respectively defining the colors of the color patches,

computing, for each one of the colors of the color patches, a color difference component between a corresponding one of the first color signal values and a corresponding one of the reference color signal values,

selecting at least one color of the color patches based on comparison of magnitude of the obtained color difference components,

computing a color correction parameter using the first color signal value corresponding to the selected color and the reference color signal value that defines the selected color, the color correction parameter being a parameter that makes the color difference component between a first corrected color signal value which is obtained by correcting the first color signal value corresponding to the selected color using the color correction parameter and the reference color signal value defining the selected color smaller than the color difference component between the first color signal value corresponding to the selected color and the reference color signal value defining the selected color,

computing a measure of accuracy using the color difference component between a second corrected color signal value which is obtained by correcting a first color signal value corresponding to a color other than the selected color using the color correction parameter and the reference color signal value that defines the color other than the selected color, and

determining accuracy of correction by comparing the measure of accuracy to a predetermined accuracy criterion, and

wherein the color correction device performs the color correction using the color correction parameters.