Luma-based color matching

• US 9,374,504 B2
• Filed: 08/18/2014
• Issued: 06/21/2016
• Est. Priority Date: 02/04/2011
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Pettigrew, Daniel, Bryant, Andrew, Fedkiw, Olivier
• Primary Examiner(s): TUCKER, WESLEY J
• Application Number:
  US14/462,514
• Publication Number:
  US 20140355878A1
• Time in Patent Office: 673 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: H04N 1/60 Colour correction or control H04N1/54 takes precedence
• CPC Class Codes: H04N 1/6005 with luminance or chrominance signals, e.g. LC1C2, HSL or YUV
• CPC Class Codes: H04N 1/6075 Corrections to the hue
• CPC Class Codes: H04N 1/62 Retouching, i.e. modification of isolated colours only or in isolated picture areas only

Abstract

Some embodiments provide a computer program for performing a color matching operation. The computer program identifies first and second images. Each image includes several pixels. Each pixel includes a luma component value. Based on analysis of the luma component values of the pixels of the first and second images, the computer program determines a set of transforms to modify pixel values of the first image so that the pixel values of the first image are similar to pixel values of the second image. The computer program applies the set of transforms to the first image such that the pixel values of the first image are similar to the pixel values of the second image.

Claims

1. A non-transitory machine readable medium storing a program which when executed by at least one processing unit performs a color matching operation, the program comprising sets of instructions for:

based on analysis of luma component values of pixels of a first image and a second image, identifying a first initial set of ranges of luma component values in the first image and a second initial set of ranges of luma component values in the second image;

splitting a range in the first initial set of ranges into two ranges in a first updated set of ranges;

splitting a corresponding range in the second initial set of ranges into two ranges in a second updated set of ranges;

for each range in the first updated set of ranges;

determining a set of transforms to modify pixel values of the pixels in the first image with luma component values in the range so that the pixel values of pixels with luma component values in the range in the first image are similar to pixel values of pixels with luma component values in a corresponding range in the second image; and

applying the set of transforms to the pixels in the first image with luma component values in the range such that the pixel values of the pixels with luma component values in the range in first image are similar to the pixel values of the pixels with luma component values in a corresponding range in the second image.

2. The non-transitory machine readable medium of claim 1, wherein the set of instructions for splitting the range in the first initial set of ranges into two ranges comprises a set of instructions for determining to split the range based on the range exceeding a threshold number of luma component values.

3. The non-transitory machine readable medium of claim 1, wherein the set of instructions for splitting the range in the first initial set of ranges into two ranges comprises a set of instructions for determining to split the range based on the corresponding range in the second image exceeding a threshold number of luma component values.

4. The non-transitory machine readable medium of claim 1, wherein the first initial set of ranges are based on a set of percentiles of the luma component values of the first image and the second initial set of ranges are based on a corresponding set of percentiles of the luma component values of the second image.

5. The non-transitory machine readable medium of claim 1, wherein each pixel further comprises a set of color component values, wherein the set of transforms to modify pixel values of the pixels with luma component values in each range of the first image so that the pixel values of the pixels with the luma component values in the range are similar to pixel values of the pixels with luma component values in the corresponding range in the second image comprises a transform to modify a set of pixels of the first image having a particular luma component value such that a first set of average color component values of the set of pixels of the first image is equivalent to a second set of average color component values of a set of pixels of the second image having the particular luma component value.

6. The non-transitory machine readable medium of claim 1, wherein each pixel further comprises a saturation component value, wherein the set of transforms to modify pixel values of the pixels with luma component values in each range of the first image so that the pixel values of the pixels with luma component values in the range of the first image are similar to pixel values of the pixels with luma component values in the corresponding range in the second image comprises a transform to modify a set of pixels of the first image having a particular luma component value such that a first average saturation component value of the set of pixels of the first image is equivalent to a second average saturation component value of a set of pixels of the second image having the particular luma component value.

7. The non-transitory machine readable medium of claim 1, wherein the program further comprises sets of instructions for:

converting the first image to a luma-based color space before analyzing the first image; and

converting the second image to the luma-based color space before analyzing the second image.

8. A non-transitory machine readable medium storing a program which when executed by at least one processing unit performs a color matching operation, the program comprising sets of instructions for:

based on analysis of luma component values of pixels of a first image and a second image, identifying a first initial set of ranges of luma component values in the first image and a second initial set of ranges of luma component values in the second image;

combining a plurality of ranges in the first initial set of ranges into a single range in a first updated set of ranges;

combining a corresponding plurality of ranges in the second initial set of ranges into a single range in a second updated set of ranges;

for each range in the first updated set of ranges;

determining a set of transforms to modify pixel values of the pixels in the first image with luma component values in the range so that the pixel values of pixels with luma component values in the range in the first image are similar to pixel values of pixels with luma component values in a corresponding range in the second image; and

applying the set of transforms to the pixels in the first image with luma component values in the range such that the pixel values of the pixels with luma component values in the range in first image are similar to the pixel values of the pixels with luma component values a corresponding range in the second image.

9. The non-transitory machine readable medium of claim 8, wherein the set of instructions for combining the plurality of ranges in the first initial set of ranges into the single range comprises a set of instructions for determining to combine the plurality of ranges based on a number of luma component values of the plurality of ranges being less than a threshold number of luma component values.

10. The non-transitory machine readable medium of claim 8, wherein the set of instructions for combining the plurality of ranges in the first initial set of ranges into the single range comprises a set of instructions for determining to combine the plurality of ranges based on the corresponding plurality of ranges in the second image being less than a threshold number of luma component values.

11. The non-transitory machine readable medium of claim 8, wherein the first initial set of ranges are based on a set of percentiles of the luma component values of the first image and the second initial set of ranges are based on a corresponding set of percentiles of the luma component values of the second image.

12. The non-transitory machine readable medium of claim 8, wherein each pixel further comprises a set of color component values, wherein the set of transforms to modify pixel values of the pixels with luma component values in each range of the first image so that the pixel values of the pixels with luma component values in the range are similar to pixel values of the pixels with luma component values in the corresponding range of the second image comprises a transform to modify a set of pixels of the first image having a particular luma component value such that a first set of average color component values of the set of pixels of the first image is equivalent to a second set of average color component values of a set of pixels of the second image having the particular luma component value.

13. The non-transitory machine readable medium of claim 8, wherein each pixel further comprises a saturation component value, wherein the set of transforms to modify pixel values of the pixels with luma component values in the each range of the first image so that the pixel values of the pixels with luma component values in the range of the first image are similar to pixel values of the pixels with luma component values in the corresponding range of the second image comprises a transform to modify a set of pixels of the first image having a particular luma component value such that a first average saturation component value of the set of pixels of the first image is equivalent to a second average saturation component value of a set of pixels of the second image having the particular luma component value.

14. The non-transitory machine readable medium of claim 8, wherein the program further comprises sets of instructions for:

converting the first image to a luma-based color space before analyzing the first image; and

converting the second image to the luma-based color space before analyzing the second image.

15. A method of performing a color matching operation on an electronic device, the method comprising:

based on analysis of luma component values of pixels of a first image and a second image, identifying a first set of ranges of luma component values in the first image and a second set of ranges of luma component values in the second image;

splitting a range in the first set of ranges into two ranges to update the first set of ranges;

splitting a corresponding range in the second set of ranges into two ranges to update the second set of ranges;

combining a plurality of ranges in the first set of ranges into a single range to update the first set of ranges;

combining a corresponding plurality of ranges in the second set of ranges to update the second set of ranges;

for each range in the first set of ranges;

determining a set of transforms to modify pixel values of the pixels in the first image with luma component values in the range so that the pixel values of pixels with luma component values in the range in the first image are similar to pixel values of pixels with luma component values in a corresponding range in the second image; and

applying the set of transforms to the pixels in the first image with luma component values in the range such that the pixel values of the pixels with luma component values in the range in first image are similar to the pixel values of the pixels with luma component values in a corresponding range in the second image.

16. The method of claim 15, wherein splitting the range in the first set of ranges into two ranges comprises determining to split the range based on the range exceeding a threshold number of luma component values.

17. The method of claim 15, wherein splitting the range in the first set of ranges into two ranges comprises determining to split the range based on the corresponding range in the second image exceeding a threshold number of luma component values.

18. The method of claim 15, wherein the first set of ranges are based on a set of percentiles of the luma component values of the first image and the second set of ranges are based on a corresponding set of percentiles of the luma component values of the second image.

19. The method of claim 15, wherein combining the plurality of ranges in the first set of ranges into the single range comprises determining to combine the plurality of ranges based on a number of luma component values of the plurality of ranges being less than a threshold number of luma component values.

20. The method of claim 15, wherein combining the plurality of ranges in the first initial set of ranges into the single range comprises determining to combine the plurality of ranges based on the corresponding plurality of ranges in the second image being less than a threshold number of luma component values.