Color image reproduction with accurate inside-gamut colors and enhanced outside-gamut colors

• US 6,400,843 B1
• Filed: 04/22/1999
• Issued: 06/04/2002
• Est. Priority Date: 04/22/1999
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Ancin, Hakan, Shu, Joseph, Bhattacharjya, Anoop, Lin, Tsung-Nan
• Primary Examiner(s): Patel, Jayanti K.
• Application Number:
  US09/296,891
• Time in Patent Office: 1,139 Days
• Field of Search: 382/162-167, 358/518, 358/500, 358/298, 358/1-9, 358/296, 358/487, 358/502, 358/505, 345/440.2, 345/590, 345/604, 345/589, 345/600, 348/391.1
• US Class Current: 382/167
• CPC Class Codes: H04N 1/6058 Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut

Abstract

A color image reproduction system achieves higher-quality color reproduction by improving the utilization of colors within the gamut of an output device that are not in the gamut of an input device. This is accomplished by a device-dependent compensation transformation that maps a second set of colors in both the gamut of an input device and the gamut of the output device into a first set of colors in the gamut of the output device but not in the gamut of the input device. The compensation transformation may be derived in a number of ways that entail identifying the first and second sets of colors and then determining one or more scaling factors that map the second set of colors into a union of the first and second sets of colors.

Claims

1. A method for developing a compensation transformation for use in a color image reproduction system that comprises an input device having an input gamut and an output device having an output gamut, the method comprising:

identifying a first set of colors that are in the output gamut but are not in the input gamut;

identifying a second set of colors that are in the input gamut and in the output gamut; and

developing the compensation transformation to enhance chromaticity of colors in the second set of colors by mapping the second set of colors into a union of the first and second sets of colors.

2. A method according to claim 1 that identifies the first set of colors by:

obtaining a first medium conveying a third set of colors in a first range of chromaticity;

scanning the first medium with the input device to obtain first color coordinates in the input gamut representing the third set of colors;

applying a first color-space transformation to obtain second color coordinates in response to the first color coordinates;

printing colors in a second range of chromaticity on a second medium in response to the second color coordinates;

applying a second color-space transformation to obtain third color coordinates in response to the first color coordinates;

printing colors in a third range of chromaticity on a third medium in response to the third color coordinates; and

comparing the second and third ranges of chromaticity and identifying which of the colors in the third set of colors are also in the first set of colors.

3. A method according to claim 1 that identifies the first set of colors by:

obtaining first color coordinates representing a third set of colors;

printing colors in a first range of chromaticity on a first medium in response to the first color coordinates;

scanning the medium with the input device to obtain second color coordinates in the input gamut;

obtaining third color coordinates in response to the second color coordinates;

printing colors in a second range of chromaticity on a second medium in response to the third color coordinates; and

comparing the first and second ranges of chromaticity and identifying which of the colors in the third set of colors are also in the first set of colors.

4. A method according to claim 1 that identifies the first set of colors by:

obtaining first color coordinates representing a third set of colors;

printing colors in a first range of chromaticity on a first medium in response to the first color coordinates;

scanning the medium with the input device to obtain second color coordinates in the input gamut representing colors in a second range of chromaticity;

scanning the medium with a calibrated measuring device to obtain third color coordinates representing colors in a third range of chromaticity; and

comparing the second and third ranges of chromaticity and identifying which of the colors in the third set of colors are also in the first set of colors.

5. A method for performing a compensation transformation in a color image reproduction system that comprises an input device having an input gamut and an output device having an output gamut, the method comprising:

receiving an input signal representing color space coordinates of a first color that is in the input gamut and in the output gamut; and

applying the compensation transformation to the input signal to generate an output signal representing color space coordinates of a second color that is in the output gamut but not in the input gamut.

6. A method according to claim 5 wherein the compensation transformation is applied to map the first color to the second color by scaling a color space coordinate of the first color.

7. A method according to claim 5 wherein the compensation transformation is applied to map the first color to the second color by interpolation of a multi-dimensional lookup table having entries representing colors that are in the output gamut but are not in the input gamut.

8. A method according to claim 5 that applies the compensation transformation to signals representing color space coordinates in the input gamut that are within a first region of color space to generate an output signal representing color space coordinates in the output gamut in a second region of color space, wherein substantially all colors that are represented in the intersection of the second region and the input gamut are also represented in the first region.

9. A method according to claim 5 that comprises:

receiving configuration signals representing characteristics of the input gamut and the output gamut; and

altering the compensation transformation according to the colors represented by color space coordinates in the output gamut that are not represented by color space coordinates in the input gamut.

10. A method according to claim 5 wherein a first set of colors are in the output gamut but not in the input gamut and a second set of colors are in the input gamut and in the output gamut, and wherein the compensation transformation maps colors from the second set of colors into a union of the first and second sets of colors.

11. An apparatus for performing a compensation transformation in a color image reproduction system that comprises an input device having an input gamut and an output device having an output gamut, the apparatus comprising:

a terminal that receives an input signal representing color space coordinates of a first color that is in the input gamut and in the output gamut; and

processing circuitry that applies the compensation transformation to the input signal to generate an output signal representing color space coordinates of a second color that is in the output gamut but not in the input gamut.

12. An apparatus according to claim 11 wherein the processing circuitry applies the compensation transformation to map the first color to the second color by scaling a color space coordinate of the first color.

13. An apparatus according to claim 11 wherein the processing circuitry applies the compensation transformation to map the first color to the second color by interpolation of a multi-dimensional lookup table having entries representing colors that are in the output gamut but are not in the input gamut.

14. An apparatus according to claim 11 wherein the processing circuitry applies the compensation transformation to signals representing color space coordinates in the input gamut that are within a first region of color space to generate an output signal representing color space coordinates in the output gamut in a second region of color space, wherein substantially all colors that are represented in the intersection of the second region and the input gamut are also represented in the first region.

15. An apparatus according to claim 11 that comprises a terminal to receive configuration signals representing characteristics of the input gamut and the output gamut, wherein processing circuitry alters the compensation transformation according to the colors represented by color space coordinates in the output gamut that are not represented by color space coordinates in the input gamut.

16. An apparatus according to claim 11 wherein a first set of colors are in the output gamut but not in the input gamut and a second set of colors are in the input gamut and in the output gamut, and wherein the compensation transformation maps colors from the second set of colors into a union of the first and second sets of colors.

17. A medium readable by a device embodying a program of instructions for execution by the device to perform a method for developing a compensation transformation for use in a color image reproduction system that comprises an input device having an input gamut and an output device having an output gamut, wherein the method comprises:

identifying a first set of colors that are in the output gamut but are not in the input gamut,

identifying a second set of colors that are in the input gamut and in the output gamut; and

developing the compensation transformation to enhance chromaticity of colors in the second set of colors by mapping the second set of colors into a union of the first and second sets of colors.

18. A medium according to claim 17 wherein the method identifies the first set of colors by:

obtaining a first medium conveying a third set of colors in a first range of chromaticity;

scanning the first medium with the input device to obtain first color coordinates in the input gamut representing the third set of colors;

applying a first color-space transformation to obtain second color coordinates in response to the first color coordinates;

printing colors in a second range of chromaticity on a second medium in response to the second color coordinates;

applying a second color-space transformation to obtain third color coordinates in response to the first color coordinates;

printing colors in a third range of chromaticity on a third medium in response to the third color coordinates; and

presenting the second and third ranges of chromaticity for comparison and identification of which colors in the third set of colors are also in the first set of colors.

19. A medium according to claim 17 wherein the method identifies the first set of colors by:

obtaining first color coordinates representing a third set of colors;

printing colors in a first range of chromaticity on a first medium in response to the first color coordinates;

scanning the medium with the input device to obtain second color coordinates in the input gamut;

obtaining third color coordinates in response to the second color coordinates;

printing colors in a second range of chromaticity on a second medium in response to the third color coordinates; and

presenting the first and second ranges of chromaticity for comparison and identification of which colors in the third set of colors are also in the first set of colors.

20. A medium according to claim 17 wherein the method identifies the first set of colors by:

obtaining first color coordinates representing a third set of colors;

printing colors in a first range of chromaticity on a first medium in response to the first color coordinates;

scanning the medium with the input device to obtain second color coordinates in the input gamut representing colors in a second range of chromaticity;

scanning the medium with a calibrated measuring device to obtain third color coordinates representing colors in a third range of chromaticity; and

presenting the second and third ranges of chromaticity for comparison and identification of which colors in the third set of colors are also in the first set of colors.

21. A medium readable by a device embodying a program of instructions for execution by the device to perform a method for performing a compensation transformation in a color image reproduction system that comprises an input device having an input gamut and an output device having an output gamut, wherein the method comprises:

receiving an input signal representing color space coordinates of a first color that is in the input gamut and in the output gamut; and

applying the compensation transformation to the input signal to generate an output signal representing color space coordinates of a second color that is in the output gamut but not in the input gamut.

22. A medium according to claim 21 wherein the method applies the compensation transformation to map the first color to the second color by scaling a color space coordinate of the first color.

23. A medium according to claim 21 wherein the method applies the compensation transformation to map the first color to the second color by interpolation of a multi-dimensional lookup table having entries representing colors that are in the output gamut but are not in the input gamut.

24. A medium according to claim 21 wherein the method applies the compensation transformation to signals representing color space coordinates in the input gamut that are within a first region of color space to generate an output signal representing color space coordinates in the output gamut in a second region of color space, wherein substantially all colors that are represented in the intersection of the second region and the input gamut are also represented in the first region.

25. A medium according to claim 21 wherein the method comprises:

receiving configuration signals representing characteristics of the input gamut and the output gamut; and

altering the compensation transformation according to the colors represented by color space coordinates in the output gamut that are not represented by color space coordinates in the input gamut.

26. A medium according to claim 21 wherein a first set of colors are in the output gamut but not in the input gamut and a second set of colors are in the input gamut and in the output gamut, and wherein the method applies the compensation transformation to map colors from the second set of colors into a union of the first and second sets of colors.