Color processing

• US 7,120,295 B2
• Filed: 07/02/2003
• Issued: 10/10/2006
• Est. Priority Date: 03/01/1999
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Fischer, Timothy A., Rozzi, William A., Edge, Christopher J.
• Primary Examiner(s): SHERALI, ISHRAT I
• Application Number:
  US10/612,734
• Publication Number:
  US 20040218811A1
• Time in Patent Office: 1,196 Days
• Field of Search: 382/162, 382/167, 358/1.9, 358/1.1, 358500-530, 345589-604
• US Class Current: 382/162
• CPC Class Codes: H04N 1/6027 Correction or control of colour gradation or colour contrast H04N1/6058 takes precedence
• CPC Class Codes: H04N 1/6052 Matching two or more picture signal generators or two or more picture reproducers

Abstract

A method of characterizing a color imaging system is provided. The method comprises obtaining first data indicative of output of the color imaging system. The first data is processed, to yield second data, according to a color appearance model that varies in accordance with neutrality of colors indicated by the first data. Other methods are provided as well as systems and computer program products for characterizing color imaging systems and devices and for producing colors.

Claims

1. A method of characterizing colors for reproduction between a first device and a second device, the method comprising:

normalizing first tristimulus values indicative of a color of the first device using local black point values;

transforming the normalized first tristimulus values to obtain color values indicative of modified cone response of the human eye;

chromatically adapting the color values from a local condition to a reference condition; and

transforming the adapted color values to obtain second tristimulus values.

2. The method of claim 1 wherein a neutral axis of the local condition is mapped to a neutral axis of the reference condition.

3. The method of claim 1 wherein normalizing the first tristimulus values includes dividing by a difference between a local luminance value and a local black point luminance value.

4. The method of claim 3 wherein transforming the adapted color values includes multiplying the adapted color values by a reference white point luminance value divided by a difference between a local white point luminance value and the local black point luminance value.

5. The method of claim 1 wherein transforming the normalized first tristimulus values is performed using a Bradford transformation.

6. The method of claim 5 wherein normalizing the first tristimulus values and transforming the normalized first tristimulus values are performed according to

$\left[\begin{array}{c}{R}_1\\ G_1\\ B_1\end{array}\right]=M_b$

[ ( X 1 - X 1 ⁢

k ) / ( Y 1 - Y 1 ⁢

k ) ( Y 1 - Y 1 ⁢

k ) / ( Y 1 - Y 1 ⁢

k ) ( Z 1 - Z 1 ⁢

k ) / ( Y 1 - Y 1 ⁢

k ) ]

where [X_1K, Y_1K, Z_1K] is the local black point, X₁, Y₁, and Z₁, are the first tristimulus values,

$M_b=\left[\begin{array}{ccc}0.8951& 0.2664& -0.1614\\ -0.7502& 1.7135& 0.0367\\ 0.0389& -0.0685& 1.0296\end{array}\right]$

where R₁, G₁, and B₁ are the color values indicative of modified cone responses of the human eye and M_b is a Bradford matrix.

7. The method of claim 6 wherein chromatically adapting the color values is performed according to

R_ref=(R_rw/R_1w)×

R₁

G_ref=(G_rw/G_1w)×

G₁

B_ref=Sign(B₁)×

(B_rw/B_1w^β

)×

|B₁|^β

β

=(B_1w/B_rw)^0.0836

where R_rw, G_rw and B_rw and RGB values of a reference white point, R_1w, G_1w, and B_1w are RGB values of a local white point, β

is an adjustment factor, and R_ref, G_ref, and B_ref are cone responses adapted from local to reference values.

8. The method of claim 7 wherein transforming the adapted color values to second tristimulus values is performed according to

$\left[\begin{array}{c}{X}_{\mathrm{ref}}\\ Y_{\mathrm{ref}}\\ Z_{\mathrm{ref}}\end{array}\right]=M_y^{-1}$

[ R ref ×

Y 1 ×

Y rw / ( Y 1 ⁢

w - Y 1 ⁢

k ) G ref ×

Y 1 ×

Y rw / ( Y 1 ⁢

w - Y 1 ⁢

k ) B ref ×

Y 1 ×

Y rw / ( Y 1 ⁢

w - Y 1 ⁢

k ) ]

where X_ref, Y_ref, and Z_ref are the second tristimulus values.

9. The method of claim 1 wherein transforming the normalized first tristimulus values is performed using a von Kries transformation.

10. The method of claim 9 wherein

$\left[\begin{array}{c}{X}_{\mathrm{ref}}\\ Y_{\mathrm{ref}}\\ Z_{\mathrm{ref}}\end{array}\right]=M_y^{-1}$

[ L rw 0 0 0 M rw 0 0 0 S rw ] ⁢

⁢

[ 1 / ( L 1 ⁢

w - L 1 ⁢

k ) 0 0 0 1 / ( M 1 ⁢

w - M 1 ⁢

k ) 0 0 0 1 / ( S 1 ⁢

w - S 1 ⁢

k ) ] ⁢

M v ⁡

[ X 1 Y 1 Z 1 ]

where

$M_y=\left[\begin{array}{ccc}0.38791& 0.68898& -0.07868\\ -0.22981& 1.18340& 0.04641\\ 0& 0& 1.0\end{array}\right]$

and where (L_ref, M_ref, S_rw) are LMS (long, medium, and short wavelength band) values for local white, (L_1k, M_1k, S_1k) are LMS values for local black X₁, Y₁, and Z₁ are the first tristimulus values, and X_ref, Y_ref, and Z_ref are the second tristimulus values.

11. The method of claim 1, wherein the first device is a print device and the second device is a print device, tristimulus values of a common illuminant are used as reference tristimulus white values for the print devices, media white tristimulus values of each of the print devices are used as local tristimulus white values for the print devices, and Bradford-type adaptations are used for the print devices to implement media-relative colorimetry.

12. The method of claim 1 wherein the first device is a print device and the second device is a display device, tristimulus values of a reference illuminant are used as reference tristimulus white values, media white tristimulus values of the print device are used as local tristimulus white values for the print device, monitor white tristimulus values of the display devices, and Bradford-type adaptations are used for the first and second devices to implement media-relative colorimetry.

13. The method of claim 1 wherein the first device is a print device and the second device is a display device, tristimulus values of a reference illuminant are used as reference tristimulus white values for the display device, media white tristimulus values of the print device are used as local tristimulus white values, monitor white tristimulus values of the display device are used as local tristimulus values for the display device, Bradford-type adaptation is used for the display device, and absolute CIE-Lab is used for the print device to implement absolute colorimetry.

14. A computer-readable medium comprising instructions for characterization of colors for reproduction between a first device and a second device, the instructions causing a processor to:

normalize first tristimulus values indicative of a color of the first device using local black point values;

transform the normalized first tristimulus values to obtain color values indicative of modified cone response of the human eye;

chromatically adapt the color values from a local condition to a reference condition; and

transform the adapted color values to obtain second tristimulus values.

15. The computer-readable medium of claim 14 wherein the instructions cause the processor to normalize the first tristimulus values by dividing by a difference between a local luminance value and a local black point luminance values,

wherein the instructions cause the processor to transform the adapted color values by multiplying the adapted color values by a reference white point luminance value divided by a difference between a local white point luminance value and the local black point luminance value, and wherein the instructions cause the processor to transform the normalized first tristimulus values using a Bradford transformation, and

wherein the instructions cause the processor to normalize the first tristimulus values and transform the normalized first tristimulus values according to:

$\left[\begin{array}{c}{R}_1\\ G_1\\ B_1\end{array}\right]=M_b<br><br>\left[\begin{array}{c}\left(X_1-X_{1<br><br>K}\right)<br><br>\text{/}<br><br>\left(Y_1-Y_{1<br><br>K}\right)\\ \left(Y_1-Y_{1<br><br>K}\right)<br><br>\text{/}<br><br>\left(Y_1-Y_{1<br><br>K}\right)\\ \left(Z_1-Z_{1<br><br>K}\right)<br><br>\text{/}<br><br>\left(Y_1-Y_{1<br><br>K}\right)\end{array}\right]$

 

where [X_1K, Y_1K, Z_1K] is the local black point, X₁, Y₁, and Z₁ are the first tristimulus values,

$M_b=\left[\begin{array}{ccc}0.8951& 0.2664& -0.1614\\ -0.7502& 1.7135& -0.0367\\ 0.0389& -0.0685& 1.0296\end{array}\right]$

and

 

where R₁, G₁, and B₁ are the color values indicative of modified cone responses of the human eye and M_b is a Bradford matrix.

16. The computer-readable medium of claim 15, wherein the instructions cause the processor to chromatically adapt the color values according to:

R_ref=(R_rw/R_1w)×

R₁

G_ref=(G_rw/G_1w)×

G₁

B_ref=Sign(B₁)×

(B_rw/B_1w^β

)×

|B₁|^β

β

=(B_1w/B_rw)^0.0836

where R_rw, G_rw and B_rw and RGB values of a reference white point, R_1w, G_1w, and B_1w are RGB values of a local white point, β

is an adjustment factor, and R_ref, G_ref, and B_ref are cone responses adapted from local to reference values and

wherein the instructions cause the processor to transform the adapted color values to second tristimulus values is performed according to;

$\left[\begin{array}{c}{X}_{\mathrm{ref}}\\ Y_{\mathrm{ref}}\\ Z_{\mathrm{ref}}\end{array}\right]=M_y^{-1}<br><br>\left[\begin{array}{c}{R}_{\mathrm{ref}}\times <br><br>Y_1\times <br><br>Y_{\mathrm{rw}}<br><br>\text{/}<br><br>\left(Y_{1<br><br>w}-Y_{1<br><br>k}\right)\\ G_{\mathrm{ref}}\times <br><br>Y_1\times <br><br>Y_{\mathrm{rw}}<br><br>\text{/}<br><br>\left(Y_{1<br><br>w}-Y_{1<br><br>k}\right)\\ B_{\mathrm{ref}}\times <br><br>Y_1\times <br><br>Y_{\mathrm{rw}}<br><br>\text{/}<br><br>\left(Y_{1<br><br>w}-Y_{1<br><br>k}\right)\end{array}\right]$

 

where X_ref, Y_ref, and Z_ref are the second tristimulus and M_y is a von Kries matrix.

17. The computer-readable medium of claim 14, wherein the instructions cause the processor to transform the normalized first tristimulus values using a von Kries transformation, wherein

$\left[\begin{array}{c}{X}_{\mathrm{ref}}\\ Y_{\mathrm{ref}}\\ Z_{\mathrm{ref}}\end{array}\right]=M_y^{-1}$

[ L rw 0 0 0 M rw 0 0 0 S rw ] ⁡

[ 1 ⁢

/ ⁢

( L 1 ⁢

w - L 1 ⁢

k ) 0 X 1 0 1 ⁢

/ ⁢

( M 1 ⁢

w - M 1 ⁢

k ) 0 0 0 1 ⁢

/ ⁢

( S 1 ⁢

w - S 1 ⁢

k ) ] ⁢

M y ⁡

[ X 1 Y 1 Z 1 ]

where

$M_y=\left[\begin{array}{ccc}0.38791& 0.68898& -0.07868\\ -0.22981& 1.18340& 0.04641\\ 0& 0& 1.0\end{array}\right]$

and where (L_ref, M_ref, S_rw) are LMS (long, medium, and short wavelength band) values for local white, (L_1k, M_1k, S_1k) are LMS values for local black X₁, Y₁, and Z₁ are the first tristimulus values, and X_ref, Y_ref, and Z_ref are the second tristimulus values and M_y is a von Kries matrix.

18. The computer-readable medium of claim 14, wherein the first-device is a print device and the second device is a print device, tristimulus values of a common illuminant are used as reference tristimulus white values for the print devices, media white tristimulus values of each print device are used as local tristimulus white values for the print devices, and Bradford-type adaptations are used for both print devices to implement media-relative colorimetry.

19. The computer-readable medium of claim 14, wherein the first device is a print device and the second device is a display device, tristimulus values of a reference illuminant are used as reference tristimulus white values, media white tristimulus values of the print device are used as local tristimulus white values for the print device, monitor white tristimulus values of the display device are used as local tristimulus values for the display device, and Bradford-type adaptations are used for the devices to implement media-relative colorimetry.

20. The computer-readable medium of claim 14, wherein the first-device is a print device and the second device is a display device, tristimulus values of a reference illuminant are used as reference tristimulus white values for the display device, media white tristimulus values of the print device are used as local tristimulus white values, monitor white tristimulus values of the display device are used as local tristimulus values for the display device, Bradford-type adaptation is used for the display device, and absolute CIE-Lab is used for the print device to implement absolute calorimetry.