Methods and apparatus for converting color values

• US 6,781,596 B2
• Filed: 05/24/2002
• Issued: 08/24/2004
• Est. Priority Date: 05/24/2002
• Status: Active Grant

• Current Assignee: Fiery LLC
• Original Assignee: Electronics For Imaging Incorporated
• Inventors: Falk, Richard
• Primary Examiner(s): Bella, Matthew C.
• Assistant Examiner(s): RAHMJOO, MANUCHER
• Application Number:
  US10/154,643
• Publication Number:
  US 20040046766A1
• Time in Patent Office: 823 Days
• Field of Search: 345/600, 345/601, 345/604, 345/606, 345/589, 345/597
• US Class Current: 345/600
• 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 converting a first color value to a second color value, the method comprising:

providing a lookup table comprising a plurality of entries, each entry associating a corresponding first value to a corresponding second value;

identifying an entry that has a corresponding second value equal to a predetermined value, and that is adjacent an entry having a corresponding second value equal to a number other than the predetermined value;

compressing the corresponding second values of a first plurality of the entries to form corresponding intermediate values; and

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

2. The method of claim 1, wherein:

identifying further comprises identifying each entry that has a corresponding second value equal to a predetermined value, and that is adjacent an entry having a corresponding second value equal to a number other than the predetermined value; and

replacing further comprises replacing the corresponding second 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.

3. The method of claim 1, wherein each of the corresponding second values has a value greater than or equal to zero (“

ZERO”

) and less than or equal to a maximum number (“

MAX”

).

4. The method of claim 3, wherein the predetermined value is ZERO.

5. The method of claim 3, wherein the predetermined value is MAX.

6. The method of claim 1, wherein:

each of the corresponding second values has a value greater than or equal to zero (“

ZERO”

) and less than or equal to a maximum number (“

MAX”

);

identifying further comprises identifying a first entry that has a corresponding second value equal to ZERO, and that is adjacent a second entry having a corresponding second value equal to a number greater than ZERO, and identifying a third entry that has a corresponding second value equal to MAX, and that is adjacent a fourth entry having a corresponding second value equal to a number less than MAX; and

replacing further comprises replacing the corresponding second value of the first entry with a value determined by a regression that includes the corresponding intermediate value of the second entry, and replacing the corresponding second value of the third entry with a value determined by a regression that includes the corresponding intermediate value of the fourth entry.

7. The method of claim 1, further comprising:

identifying a fifth entry that has a corresponding first value equal to the first color value; and

setting an intermediate color value equal to the corresponding intermediate value of the fifth entry.

8. The method of claim 7, further comprising decompressing the intermediate color value to provide the second color value.

9. The method of claim 1, further comprising:

identifying a second plurality of entries that have corresponding first values that surround the first color value; and

setting an intermediate color value equal to a value determined by interpolating the corresponding intermediate values of the second plurality of entries.

10. The method of claim 9, further comprising decompressing the intermediate color value to provide the second color value.

11. A method for creating a color conversion lookup table, the method comprising:

creating a plurality of table entries, each entry associating a corresponding first value to a corresponding second value;

identifying the minimum and maximum 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;

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.

12. The method of claim 11, wherein:

each of the corresponding second values has a first bit-length; and

the creating step further comprises converting the corresponding second values to values having a second bit length.

13. The method of claim 12, wherein the second bit length is greater than the first bit length.