Methods and apparatus for converting color values

• US 20060007241A1
• Filed: 09/09/2005
• Published: 01/12/2006
• Est. Priority Date: 05/24/2002
• Status: Active Grant

• Current Assignee: Fiery LLC
• Original Assignee: Electronics For Imaging Incorporated
• Inventors: Falk, Richard
• Granted Patent: US 7,259,768 B2
• Time in Patent Office: Days
• US Class Current: 345/601
• CPC Class Codes: G06F 3/13 Digital output to plotter ; Cooperation and interconnection of the plotter with other functional units
• CPC Class Codes: G09G 2340/02 Handling of images in compressed format, e.g. JPEG, MPEG
• CPC Class Codes: G09G 2340/06 Colour space transformation
• 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
• CPC Class Codes: G09G 5/06 using colour palettes, e.g. look-up tables
• CPC Class Codes: H04N 1/6019 using look-up tables H04N1/6025 takes precedence

Abstract

Color conversion apparatus and methods are provided for converting a first color value, such as an RGB, L*a*b* or XYZ color value, to a second color value, such as an RGB, CMY, CMKY, L*a*b*, L, C₁C₂, or XYZ color value, without saturation error.

Claims

1. A method for modifying a color conversion lookup table that includes a plurality of table entries, each entry associating a corresponding first value to a corresponding second value, the method comprising:

identifying the minimum values of the plurality of corresponding second values;

identifying table entries that have corresponding second values equal to the minimum value, and that are adjacent an entry having a corresponding second value greater than the minimum value;

compressing the corresponding second value of each of the table entries to form corresponding intermediate values; and

replacing the corresponding intermediate value of each of the identified entries with a value determined by a regression that includes the corresponding intermediate value of the corresponding adjacent entry.

2. The method of claim 1, wherein each of the corresponding second values has a first bit-length, and the method further comprises converting the corresponding second values to values having a second bit length.

3. The method of claim 2, wherein the second bit length is greater than the first bit length.

4. The method of claim 1, wherein compressing comprises linearly compressing the corresponding second value of each of the table entries.

5. The method of claim 1, wherein compressing comprises multiplying the corresponding second value of each of the table entries by a scale factor.

6. The method of claim 1, wherein compressing comprises adding a constant value to the corresponding second value of each of the table entries.

7. The method of claim 1, wherein the regression comprises linear extrapolation.

8. A method for modifying a color conversion lookup table that includes a plurality of table entries, each entry associating a corresponding first value to a corresponding second value, the method comprising:

identifying the maximum values of the plurality of corresponding second values;

identifying table entries that have corresponding second values equal to the maximum value, and that are adjacent an entry having a corresponding second value less than the maximum value;

compressing the corresponding second value of each of the table entries to form corresponding intermediate values; and

replacing the corresponding intermediate value of each of the identified entries with a value determined by a regression that includes the corresponding intermediate value of the corresponding adjacent entry.

9. The method of claim 8, wherein each of the corresponding second values has a first bit-length, and the method further comprises converting the corresponding second values to values having a second bit length.

10. The method of claim 9, wherein the second bit length is greater than the first bit length.

11. The method of claim 8, wherein compressing comprises linearly compressing the corresponding second value of each of the table entries.

12. The method of claim 8, wherein compressing comprises multiplying the corresponding second value of each of the table entries by a scale factor.

13. The method of claim 8, wherein compressing comprises adding a constant value to the corresponding second value of each of the table entries.

14. The method of claim 8, wherein the regression comprises linear extrapolation.

15. A machine readable medium storing instructions structured to cause a machine to modify a color conversion lookup table that includes a plurality of table entries, each entry associating a corresponding first value to a corresponding second value, the instructions causing the machine to:

identify the minimum values of the plurality of corresponding second values;

identify table entries that have corresponding second values equal to the minimum value, and that are adjacent an entry having a corresponding second value greater than the minimum value;

compress the corresponding second value of each of the table entries to form corresponding intermediate values; and

replace the corresponding intermediate value of each of the identified entries with a value determined by a regression that includes the corresponding intermediate value of the corresponding adjacent entry.

16. The machine readable medium of claim 15, wherein each of the corresponding second values has a first bit-length, and the instructions further cause the machine to convert the corresponding second values to values having a second bit length.

17. The machine readable medium of claim 16, wherein the second bit length is greater than the first bit length.

18. The machine readable medium of claim 15, wherein the instructions further cause the machine to linearly compress the corresponding second value of each of the table entries.

19. The machine readable medium of claim 15, wherein the instructions further cause the machine to multiply the corresponding second value of each of the table entries by a scale factor.

20. The machine readable medium of claim 15, wherein the instructions further cause the machine to add a constant value to the corresponding second value of each of the table entries.

21. The machine readable medium of claim 15, wherein the regression comprises linear extrapolation.

22. A machine readable medium storing instructions structured to cause a machine to modify a color conversion lookup table that includes a plurality of table entries, each entry associating a corresponding first value to a corresponding second value, the instructions causing the machine to:

identify the maximum values of the plurality of corresponding second values;

identify table entries that have corresponding second values equal to the maximum value, and that are adjacent an entry having a corresponding second value less than the maximum value;

compress the corresponding second value of each of the table entries to form corresponding intermediate values; and

replace the corresponding intermediate value of each of the identified entries with a value determined by a regression that includes the corresponding intermediate value of the corresponding adjacent entry.

23. The machine readable medium of claim 22, wherein each of the corresponding second values has a first bit-length, and the instructions further cause the machine to convert the corresponding second values to values having a second bit length.

24. The machine readable medium of claim 23, wherein the second bit length is greater than the first bit length.

25. The machine readable medium of claim 22, wherein the instructions further cause the machine to linearly compress the corresponding second value of each of the table entries.

26. The machine readable medium of claim 22, wherein the instructions further cause the machine to multiply the corresponding second value of each of the table entries by a scale factor.

27. The machine readable medium of claim 22, wherein the instructions further cause the machine to add a constant value to the corresponding second value of each of the table entries.

28. The machine readable medium of claim 22, wherein the regression comprises linear extrapolation.