METHOD AND APPARATUS FOR EVALUATING COLOR IN AN IMAGE

• US 20130322750A1
• Filed: 08/08/2013
• Published: 12/05/2013
• Est. Priority Date: 10/04/2010
• Status: Active Grant

• Current Assignee: Datacolor AG Europe (Datacolor AG)
• Original Assignee: Datacolor Holding AG
• Inventors: Agarwal, Niraj, Wei, Hong
• Granted Patent: US 9,076,068 B2
• Time in Patent Office: Days
• US Class Current: 382/165
• CPC Class Codes: G01J 3/462 Computing operations in or between colour spaces; Colour management systems
• CPC Class Codes: G01J 3/463 Colour matching
• CPC Class Codes: G01J 3/50 using electric radiation detectors
• CPC Class Codes: G01J 3/524 Calibration of colorimeters
• CPC Class Codes: H04N 1/6033 using test pattern analysis H04N1/6055 takes precedence

Abstract

A method for evaluating a color of a sample includes acquiring a color calibrated swatch of the sample, the color calibrated swatch comprising a plurality of pixels, and comparing all pixels that are of a first color in a swatch of a standard to all of the plurality of pixels that are of a second color, wherein the second color is a color in the swatch of the sample that is most similar to the first color in the swatch of the standard.

Claims

1. A method for evaluating a color of a sample, the method comprising:

acquiring a color calibrated swatch of the sample, the color calibrated swatch comprising a plurality of pixels; and

comparing all pixels that are of a first color in a swatch of a standard to all of the plurality of pixels that are of a second color, wherein the second color is a color in the swatch of the sample that is most similar to the first color in the swatch of the standard.

2. The method of claim 1, wherein the swatch of the sample and the swatch of the standard are both XYZ tristimulus images.

3. The method of claim 1, wherein the swatch of the sample and the swatch of the standard are both display RGB images.

4. The method of claim 3, further comprising, prior to the comparing:

computing a first set of XYZ tristimulus values for display RGB values in the swatch of the standard;

computing a second set of XYZ tristimulus values for display RGB values in the swatch of the sample; and

computing a color difference between a plurality of colors in the swatch of the standard and a plurality of colors in the swatch of the sample based on the first set of XYZ tristimulus values and the second set of XYZ tristimulus values, wherein a color difference between the first color and the second color is smallest among all color differences computed.

5. The method of claim 4, further comprising:

quantizing colors in the swatch of the standard, prior to computing the first set of XYZ tristimulus values; and

quantizing colors in the swatch of the sample, prior to computing the second set of XYZ tristimulus values.

6. The method of claim 5, wherein the quantizing the swatch of the standard produces a first color palette of the swatch of the standard and a first color frequency array of indexed colors in the swatch of the standard, and wherein the quantizing the swatch of the sample produces a second color palette of the swatch of the sample and a second color frequency array of indexed colors in the swatch of the sample.

7. The method of claim 6, wherein each row of the first color palette represents a color in the swatch of the standard, and each column of the first color palette represents a R, G, or B value for a color in the swatch of the standard, and wherein each row of the second color palette represents a color in the swatch of the sample, and each column of the second color palette represents a R, G, or B value for a color in the swatch of the sample.

8. The method of claim 7, wherein the first color frequency array comprises a histogram of a total number of pixels of each of the indexed colors in the swatch of the standard, and wherein the second color frequency array comprises a histogram of a total number of pixels of each of the indexed colors in the swatch of the sample.

9. The method of claim 4, wherein the computing a first set of XYZ tristimulus values comprises:

linearizing each of the display RGB values in the swatch of the standard with respect to energy to produce a first plurality of linearized values; and

mapping each of the first plurality of linearized values to the first set of XYZ values according to an s-RGB color space,

and wherein the computing a second set of XYZ tristimulus values comprises;

linearizing each of the display RGB values in the swatch of the sample with respect to energy to produce a second plurality of linearized values; and

mapping each of the second plurality of linearized values to the second set of XYZ values according to the s-RGB color space.

10. The method of claim 4, wherein the computing the color difference produces an array that relates the second color to the first color.

11. The method of claim 1, further comprising:

computing a first set of weighted mean RGB values for the swatch of the standard;

computing a second set of weighted mean RGB values for the swatch of the sample; and

calculating a color difference between the first color and the second color, based on the first set of weighted mean RGB values and the second set of weighted mean RGB values.

12. The method of claim 11, further comprising:

converting display RGB values of the swatch of the standard into a first set of XYZ tristimulus values prior to the calculating; and

converting display RGB values of the swatch of the sample into a second set of XYZ tristimulus values prior to the calculating.

13. A computer readable storage device containing an executable program for evaluating a color of a sample, where the program performs steps comprising:

acquiring a color calibrated swatch of the sample, the color calibrated swatch of the sample comprising a plurality of pixels; and

comparing all pixels that are of a first color in a swatch of a standard to all of the plurality of pixels that are of a second color, wherein the second color is a color in the swatch of the sample that is most similar to the first color in the swatch of the standard.

14. A method for performing a color comparison between a first swatch comprising a first set of pixels and a second swatch comprising a second set of pixels, the method comprising:

computing a first set of weighted mean RGB values for the first swatch;

computing a second set of weighted mean RGB values for the second swatch; and

calculating a color difference between the first swatch and the second swatch, based on the first set of weighted mean RGB values and the second set of weighted mean RGB values.

15. The method of claim 14, wherein the calculating disregards a color that is present in the second swatch, but outside a threshold distance from any color in the first swatch.

16. The method of claim 14, wherein the calculating disregards a spatial distribution of colors in the first swatch and a spatial distribution of colors in the second swatch.

17. The method of claim 14, further comprising:

generating a list, the list comprising a plurality of pairs of colors, each of the plurality of pairs of colors including a color from the first swatch and a color from the second swatch that is closest among all colors in the second swatch to the color from the first swatch.

18. The method of claim 17, further comprising:

calculating a percentage of colors present in the second swatch that are also present in the first swatch.

19. The method of claim 14, further comprising:

generating a list, the list comprising a plurality of pairs of colors, each of the plurality of pairs of colors including a color from the second swatch and a color from the first swatch that is closest among all colors in the first swatch to the color from the second swatch.

20. The method of claim 19, further comprising:

calculating a percentage of colors present in the first swatch that are also present in the second swatch.