Color matching method, color matching apparatus and medium having a machine-readable product

• US 6,560,358 B1
• Filed: 10/04/1999
• Issued: 05/06/2003
• Est. Priority Date: 10/09/1998
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Tsukada, Masato
• Primary Examiner(s): Tran, Phuoc
• Assistant Examiner(s): SHERALI, ISHRAT I
• Application Number:
  US09/411,829
• Time in Patent Office: 1,310 Days
• Field of Search: 382/162, 382/166-167, 382/300-301, 358/500, 358/501, 358/529, 358/516, 358/518, 358/296, 358/520, 358/1.9, 358/525, 345/589, 345/593, 345/597-605, 345/606, 348/655
• US Class Current: 382/167
• CPC Class Codes: H04N 1/603 controlled by characteristics of the picture signal generator or the picture reproducer
• CPC Class Codes: H04N 1/6088 by viewing conditions, i.e. conditions at picture output

Abstract

Color matching method in which the color apparatus of a color image is adapted to be coincident between color image devices having significantly different reference whites with a small processing volume. From correlated color temperature of an originating reference white and a target reference white, spectral power distribution characteristics of an originating and a target color space are restored. Tristimulus values of the color in the target color space is obtained from the adaptive surface reflectance of the optional color, spectral power distribution characteristics of the target color space and the human color matching functions.

Claims

1. A color matching method for converting an optional color in an originating color space to a color in a target color space, keeping the color appearance, characterized by comprising the steps of:

(a) restoring spectral power distribution characteristics of an originating color space from a correlated color temperature of an originating reference white which is the reference white in the originating color space, and restoring spectral power distribution characteristics of a target color space from a correlated color temperature of a target reference white which is the reference white in said target color space;

(b) restoring, as a surface reflectance of the originating reference white, a first white surface reflectance from tristimulus values of the originating reference white, said spectral power distribution characteristics of the originating color space and human color matching functions, and also restoring a second white surface reflectance from tristimulus values of said originating reference white, spectral power distribution characteristics of said target color space and the human color matching functions;

(c) obtaining an adaptive white surface reflectance through interpolation of the first and second white surface reflectances;

(d) calculating a ratio of the first white surface reflectance to the adaptive white surface reflectance to obtain a spectral chromatic adaptation ratio;

(e) restoring a surface reflectance of said optional color in said originating color space by employing tristimulus values of said optional color, spectral power distribution characteristics of said originating color space and the human color matching functions;

(f) multiplying said surface reflectance of the optional color with said spectral chromatic adaptation ratio to obtain an adaptive surface reflectance of said optional color; and

(g) finding tristimulus values of the color in said target color space from the adaptive surface reflectance of said optional color, the spectral power distribution characteristics of said target color space and the human color matching functions.

2. The color matching method as defined in claim 1

wherein in said step (c) of obtaining adaptation white surface reflectance through interpolation of said first and second white surface reflectances, an incomplete chromatic adaptation coefficient is changed responsive to the state of incomplete chromatic adaptation in the human visual system, the degree of interpolation of said first and second white surface reflectances is freely changed to obtain said adaptation white surface reflectance.

3. The color matching method as defined in claim 2, further comprising the step of:

calculating an optimum incomplete chromatic adaptation coefficient from combination of the reference white of said originating color space and the reference white of said target color space, said incomplete chromatic adaptation coefficient obtained from said optimum incomplete chromatic adaptation coefficient calculating step being used.

17. The color matching method as defined in claim 1, wherein the step d) is performed in accordance with the following equation:

4. A color matching apparatus for converting an optional color in an originating color image device to a color in a target color image device, keeping the color appearance, characterized by comprising:

(a) means for restoring spectral power distribution characteristics of an originating color space from a correlated color temperature of an originating reference white which is the reference white of said originating color image device, and restoring spectral power distribution characteristics of the target color space from a correlated color temperature of a target reference white which is the reference white of said target color image device;

(b) means for restoring, as a surface reflectance of said originating reference white, a first white surface reflectance from tristimulus values of the originating reference white, said spectral power distribution characteristics of said originating color space and human color matching functions, and also restoring a second white surface reflectance from tristimulus values of said originating reference white, spectral power distribution characteristics of said target color space and human color matching functions;

(c) means for obtaining an adaptive white surface reflectance through interpolation of the first and second white surface reflectances;

(d) means for calculating a ratio of the first white surface reflectance to the adaptive white surface reflectance to obtain a spectral chromatic adaptation ratio;

(e) means for restoring a surface reflectance of said optional color in said originating color image device by employing tristimulus values of said optional color, spectral power distribution characteristics of said originating color space and the human color matching functions;

(f) means for multiplying said surface reflectance of the optional color with said spectral chromatic adaptation ratio to obtain an adaptive surface reflectance of said optional color;

(g) means for finding tristimulus values of the color in said target color image device from the adaptive surface reflectance of said optional color, the spectral power distribution characteristics of said target color space and the human color matching functions, and

(h) means for converting the tristimulus values of the color in said target color image device into device color data of said target color image device.

5. The color matching apparatus as defined in claim 4

wherein in said means for obtaining adaptive white surface reflectance through interpolation of the first and second white surface reflectances, an incomplete chromatic adaptation coefficient is changed responsive to the state of incomplete chromatic adaptation in the human visual system, the degree of interpolation of said first and second white surface reflectances is freely changed to obtain said adaptive white surface reflectance.

6. The color matching apparatus as defined in claim 5, further comprising:

means for calculating an optimum incomplete chromatic adaptation coefficient from combination of the reference white of said originating color image device and the reference white of said target color image device, said incomplete chromatic adaptation coefficient obtained from said optimum incomplete chromatic adaptation coefficient calculating means being used.

7. The color matching apparatus as defined in claim 4

wherein a color image display device is provided in the originating image device and a color image display device is provided in the target color image device.

8. The color matching apparatus as defined in claim 4

wherein a color image display device is provided in the originating image device and a color image print device is provided in the target color image device for color reproduction with multiple color inks;

there being provided means for calculating ink quantity calculating as means for converting the tristimulus values of the color in said target color image device.

9. The color matching apparatus as defined in claim 4

wherein there is provided a color image input device in the originating color image device by providing means for calculating the correlated color temperature of the reference white from chromaticity of the reference white of the color image device.

14. The color matching apparatus as defined in claim 6,

wherein a color image display device is provided in the originating image device and a color image display device is provided in the target color image device.

15. The color matching apparatus as defined in claim 6,

wherein a color image display device is provided in the originating image device and a color image print device is provided in the target color image device for color reproduction with multiple color inks;

there being provided means for calculating ink quantity calculating as means for converting the tristimulus values of the color in said target color image device.

16. The color matching apparatus as defined in claim 8,

wherein there is provided a color image input device in the originating color image device by providing means for calculating the correlated color temperature of the reference white from chromaticity of the reference white of the color image device.

18. The color matching apparatus as defined in claim 4, wherein the means for obtaining an adaptive white surface reflectance performs a calculation in accordance with the following equation:

10. A machine-readable program product performing, on a computer, the following program steps comprising:

(a) restoring spectral power distribution characteristics of an originating color space from a correlated color temperature of an originating reference white which is the reference white of an originating color image device, and restoring spectral power distribution characteristics of a target color space from a correlated color temperature of a target reference white which is the reference white of a target color image device;

(b) restoring, as a surface reflectance of said reference white, a first white surface reflectance from tristimulus values of the reference white, said spectral power distribution characteristics of said originating color space and human color matching functions, and also restoring a second white surface reflectance from tristimulus values of said originating reference white, spectral power distribution characteristics of said target color space and human color matching functions;

(c) obtaining an adaptive white surface reflectance through interpolation of the first and second white surface reflectances;

(d) calculating a ratio of the first white surface reflectance to the adaptive white surface reflectance to obtain a spectral chromatic adaptation ratio;

(e) restoring a surface reflectance of said optional color in said originating color image device by employing said tristimulus values of said optional color, spectral power distribution characteristics of said originating color space and the human color matching functions;

(f) multiplying said surface reflectance of the optional color with said spectral chromatic adaptation ratio to obtain an adaptive surface reflectance of said optional color;

(g) finding tristimulus values of the color in said target color image device from the adaptive surface reflectance of said optional color, the spectral power distribution characteristics of said target color space and the human color matching functions; and

(h) converting the tristimulus values of the color in said target color image device into device color data of said target color image device.

11. A machine-readable medium having said program product as defined in claim 10.

19. The machine-readable program product as defined in claim 10, wherein the program step d) is performed in accordance with the following equation:

12. A machine-readable program product performing, on a computer,

(a) computing correlated color temperature of a reference white from chromaticity of a reference white of a color image device;

(b) restoring spectral power distribution characteristics of an originating color space from a correlated color temperature of an originating reference white which is the reference white of an originating color image device, and restoring spectral power distribution characteristics of a target color space from a correlated color temperature of a target reference white which is the reference white of a target color image device;

(c) restoring, as a surface reflectance of said reference white, a first white surface reflectance from tristimulus values of the reference white, said spectral power distribution characteristics of said originating color space and human color matching functions, and also restoring a second white surface reflectance from tristimulus values of said originating reference white, spectral power distribution characteristics of said target color space and human color matching functions;

(d) obtaining an adaptive white surface reflectance through interpolation of the first and second white surface reflectances;

(e) calculating a ratio of the first white surface reflectance to the adaptive white surface reflectance to obtain a spectral chromatic adaptation ratio;

(f) restoring a surface reflectance of said optional color in said originating color image device by employing said tristimulus values of said optional color, spectral power distribution characteristics of said originating color space and the human color matching functions;

(g) multiplying said surface reflectance of the optional color with said spectral chromatic adaptation ratio to obtain an adaptive surface reflectance of said optional color;

(h) finding tristimulus values of the color in said target color image device from the adaptive surface reflectance of said optional color, the spectral power distribution characteristics of said target color image device and the human color matching functions; and

(i) converting tristimulus values of the color in said target color image device into device color data of said target color image device.

13. A machine-readable medium having said program product as defined in claim 12.

20. The machine-readable program product as defined in claim 12, wherein the program step d) is performed in accordance with the following equation: