Method and system for correcting color display based upon ambient light

• US 5,956,015 A
• Filed: 12/18/1995
• Issued: 09/21/1999
• Est. Priority Date: 12/18/1995
• Status: Expired due to Term

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Hino, Makoto
• Primary Examiner(s): Nguyen, Chanh
• Assistant Examiner(s): SURACI, JOHN F
• Application Number:
  US08/574,307
• Time in Patent Office: 1,373 Days
• Field of Search: 345/150, 345/153, 345/147, 345/154, 345/904, 348/658, 348/602, 348/603, 348/179, 348/655, 348/180, 348/807, 348/806
• US Class Current: 345/600
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 2340/14 Solving problems related to the presentation of information to be displayed
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 5/02 characterised by the way in which colour is displayed details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607

Abstract

The color matching methods and systems according to the current invention accomplish accurate color matching by separating causes for creating color discrepancies in a predetermined color patch on an image-carrying medium and a color monitor display. In general, the chromaticity values of the predetermined color patch are measured under a standard calorimeter light source whose luminance is different from that of ambient light. The corresponding color is displayed based upon the luminance of the standard light. However, ambient light does not generally have the above luminance. Thus, when the color display is compared against the color patch under ambient light, the colors do not appear identical. To solve this and other problems, the current invention discloses methods and systems to adjust the display signals based upon the luminance of ambient light.

Claims

1. A method of color matching between a display monitor and an image-carrying substrate, comprising the steps of:

a) comparing a predetermined color patch on the image-carrying substrate with a corresponding color output on the display monitor under a light condition, said predetermined color patch being specified by a first set of known values according to a first color system, said corresponding color output being generated based upon a second set of signals according to a second color system, said first set of values including CIE tri-stimulus x, y, and z values while said second set of signals including RGB signals;

b) making a change in said y value which is an intensity related value of said first set of said values so that said predetermined color patch and said corresponding color output on the display monitor appear substantially identical in their color representation, said step b) further comprising;

iii) converting said Y value into a L* value defining luminance by a first equation, L*=116 (Y/Y_n)^1/3 -16, Y_n being defined as 100.

iv) modifying said L* value by luminance conversion coefficients α and

β

into L'"'"'* which is defined by α

(L*-β

); and

v) converting said L'"'"'* back to a modified a Y'"'"' value which is defined by Y_n ((L'"'"'*+16)/116)³ ; and

c) generating each of said signals of said second set based upon said change in said intensity related value in said first set.

2. The method of color matching according to claim 1 wherein said step b) further comprises an additional steps of:

i) taking a measurement of said light condition; and

ii) automatically adjusting said Y value based upon said measurement.

3. The method of color matching according to claim 2 further comprising an additional step of indicating that said measurement is outside of a predetermined range of values.

4. The method of color matching according to claim 1 wherein said Y'"'"' value along with said X and Z values are substituted in the following equation for determining R'"'"'_C, G'"'"'_C and B'"'"'_C :

##EQU4## where K_R, K_G and K_B are predetermined.

5. The method of color matching according to claim 1 wherein said luminance conversion coefficients α

and β

are predetermined and stored in a memory.

6. The method of color matching according to claim 1 wherein said luminance conversion coefficients α

and β

are determined on the fly.

7. The method of color matching according to claim 1 wherein said predetermined color patch and said corresponding color output are compared under a substantially identical light condition in said step a).

8. The method of color matching according to claim 1 wherein said predetermined color patch and said corresponding color output are compared under different light conditions in said step a).

9. The method of color matching according to claim 8 wherein said corresponding color output is viewed in a dark room.

10. The method of color matching according to claim 8 wherein said first set of known values are adjusted based upon said different light conditions.

11. A method of correcting predetermined CIE XYZ values of a color patch into RGB values for a viewer under ambient light, comprising the steps of:

a) taking a measurement of the ambient light of substantially identical chromaticity coordinates of those for the predetermined CIE XYZ;

b) adjusting the RGB values based upon the measurement for a color presentation on a monitor; and

c) further adjusting the RGB values until the viewer perceives that the color presentation matches the color patch, said step c) further comprising;

d) determining luminous conversion coefficients α and

β

;

i) converting the Y value into a luminance L* value according to a conversion equation L*=116 (Y/Y_n)^1/3 -16, Y_n being defined as 100;

ii) modifying the L* value by luminance conversion coefficients α and

β

into L'"'"'* which is defined by α

(L*-β

); and

iii) converting the L'"'"'* back to a modified a Y'"'"' value which is defined by Y_n ((L'"'"'*+16)/116)³ ; and

e) storing said luminous conversion coefficients α and

β

.

12. The method of correcting predetermined CIE XYZ values according to claim 11 wherein said Y'"'"' value along with said X and Z values are substituted in the following equation for determining R'"'"'_c, G'"'"'_c and B'"'"'_c :

##EQU5## where K_R, K_G and K_B are predetermined.

13. The method of correcting predetermined CIE XYZ values according to claim 11 wherein the ambient light and a light under which the predetermined CIE XYZ values were measured have different chromaticity coordinates.

14. The method of correcting predetermined CIE XYZ values according to claim 13 further comprising additional steps of:

d) adjusting the chromaticity coordinates of the CIE XYZ values until the viewer perceives that the chromaticity coordinates of the CIE XYZ values and the RGB values have the substantially same;

e) determining luminance conversion coefficients α and

β

; and

f) storing the luminance conversion coefficients α and

β

.

15. The method of correcting predetermined CIE XYZ values according to claim 14 wherein said step e) further comprises additional steps of:

i) converting the Y value into a luminance L* value according to a conversion equation L*=116 (Y/Y_n)^1/3 -16, Y_n being defined as 100;

ii) modifying the L* value by luminance conversion coefficients α and

β

into L'"'"'* which is defined by α

(L*-β

); and

iii) converting the L'"'"'* back to a modified a Y'"'"' value which is defined by Y_n ((L'"'"'*+16)/116)³.

16. The method of correcting a color representation on according to claim 15 wherein said Y'"'"' value along with said X and Z values are substituted in the following equation for determining R'"'"'_C, G'"'"'_C and B'"'"'_C :

##EQU6## where K_R, K_G and K_B are predetermined.

17. A system for color matching between a display monitor and an image-carrying substrate, comprising:

a predetermined color patch on the image-carrying substrate, said predetermined color patch being specified by a first set of values including x, y and z values according to a first color system of CIE tri-stimulus under a predetermined light condition;

an output device for outputting a color output corresponding to said predetermined color patch, said corresponding color output being generated based upon a second set of R, G and B signals according to a second color system of RGB;

a light measuring device for taking a measurement of said light condition,

a controller connected to said light measuring device for varying an intensity related value of said y value based upon said measurement so as to cause the corresponding color output from said output device appear substantially identical to said color patch, said controller further comprising a converter for converting said Y value into a L* value defining luminance by a first equation, L*=116 (Y/Y_n)^1/3 -16, Y_n being defined as 100, said converter modifying said L* value by luminance conversion coefficients α and

β

into L'"'"'* which is defined by α

(L*-β

), said convertor converts said L'"'"'* back to a modified a Y'"'"' value which is defined by Y_n ((L'"'"'*+16)/116)³ ; and

a signal generator connected to said controller and said output device for generating each of said signals of said second set based upon said varied intensity related value in said first set.

18. The system for color matching according to claim 17 further comprising an warning indicator for indicating that said measurement is outside of a predetermined range of values.

19. The system for color matching according to claim 17 wherein said signal generator generates said RGB values based upon Y'"'"' value along with said X and Z values, R'"'"'_C, G'"'"'_C and B'"'"'_C being generated based upon the following equation:

##EQU7## where K_R, K_G and K_B are predetermined.

20. The system for color matching according to claim 17 further comprising a memory for storing predetermined sets of said luminance conversion coefficients α

and β

.

21. The system for color matching according to claim 17 wherein said luminance conversion coefficients are determined on the fly.

22. The system for color matching according to claim 17 wherein said predetermined color patch and said display monitor are placed under a substantially identical light condition.

23. The system for color matching according to claim 17 wherein said predetermined color patch and said display monitor are displayed under a different light condition.

24. The system for color matching according to claim 23 wherein said display monitor is placed in a dark room.

25. The system for color matching according to claim 23 further comprising an adjuster for adjusting said first set of known values based upon said different light condition.

26. A system for converting predetermined CIE XYZ values of a color patch into RGB values of a monitor for viewing under ambient light, comprising:

a light measuring device for taking a measurement of the ambient light of substantially identical chromaticity coordinates of those for the predetermined CIE XYZ;

a first adjustor for adjusting the RGB values based upon the measurement for a color presentation on said monitor, said first adjustor including;

a determining device for determining luminance conversion coefficients α

and β

; and

a memory for storing the luminance conversion coefficients α and

β

;

said determining device converts the Y value into a luminance L* value according to a conversion equation L*=116 (Y/Y_n)^1/3 -16, Y_n being defined as 100, said determining device modifying the L* value by luminance conversion coefficients α and

β

into L'"'"'* which is defined by α

(L*-β

), said determining device converting the L'"'"'* back to a modified a Y'"'"' value which is defined by Y_n ((L'"'"'*+16)/116)³ ; and

a second adjustor for further adjusting the RGB values until the viewer perceives that the color presentation and the color patch are substantially identical.

27. The system for converting predetermined CIE XYZ values according to claim 26 wherein said second adjustor generates R'"'"'_C, G'"'"'_C and B'"'"'_C based upon said Y'"'"' value along with said X and Z values using the following equation:

##EQU8## where K_R, K_G and K_B are predetermined.

28. The system for converting predetermined CIE XYZ values according to claim 26 wherein the ambient light and light under which the predetermined CIE XYZ values are measured have different chromaticity coordinates.

29. The system for converting predetermined CIE XYZ values according to claim 28 further comprising:

a color coordinate adjustor for adjusting the color coordinates of the CIE XYZ values so that the color patch and the color presentation are perceived substantially identical;

a luminance adjustor for adjusting said Y value based upon the ambient light; and

a memory for storing the luminance conversion coefficients α and

β

.

30. The system for converting predetermined CIE XYZ values according to claim 29 wherein said luminance adjustor converts the Y value into a luminance L* value according to a conversion equation L*=116 (Y/Y_n)^1/3 -16, Y_n being defined as 100;

said luminance adjustor modifying the L* value by luminance conversion coefficients α and

β

into L'"'"'* which is defined by α

(L'"'"'*-β

), said luminance adjustor converting the L'"'"'* back to a modified a Y'"'"' value which is defined by Y_n ((L'"'"'*+16)/116)³.

31. The system for correcting a color representation on according to claim 30, wherein said second adjustor generates R'"'"'_C, G'"'"'_C and B'"'"'_C based upon said Y'"'"' value along with said X and Z values using the following equation:

##EQU9## where K_R, K_G and K_B are predetermined.