Color Space Appearance Model Video Processor

• US 20080055479A1
• Filed: 09/04/2007
• Published: 03/06/2008
• Est. Priority Date: 09/01/2006
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Shehata, Shereef, Chang, Weider
• Granted Patent: US 9,049,408 B2
• Time in Patent Office: Days
• US Class Current: 348/652
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• 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: H04N 9/64 Circuits for processing colour signals H04N9/77 takes precedence; camera processing pipelines for processing colour signals H04N23/84
• CPC Class Codes: H04N 9/643 Hue control means, e.g. flesh tone control
• CPC Class Codes: H04N 9/646 for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters
• CPC Class Codes: H04N 9/67 for matrixing camera processing pipelines for matrixing of colour signals H04N23/85
• CPC Class Codes: H04N 9/68 for controlling the amplitude of colour signals, e.g. automatic chroma control circuits H04N9/71, H04N9/73 take precedence; camera processing pipelines for controlling the colour saturation of colour signals H04N23/86
• CPC Class Codes: H04N 9/73 Colour balance circuits, e.g. white balance circuits or colour temperature control camera processing pipelines for colour balance H04N23/88

Abstract

A method of color processing determines whether a pixel color is within at least one range of predetermined colors corresponding to a viewer expected color. If so, the method altering the pixel color to better approximate the viewer expected color. For detection of skin tones determining whether the pixel color is within a range of predetermined colors includes discounting an illuminant of the pixel color. The viewer expected colors are preferably skin tone, grass green and sky blue. The saturation level of grass green and sky blue are enhanced and that of skin tones are suppressed. The saturation s is limited based upon lightness J and hue h to convert to an allowable RGB color format range.

Claims

1. A method of color processing comprising:

receiving frames of video data;

for each pixel of each frame determining whether a pixel color of said pixel said pixel color is within at least one range of predetermined colors corresponding to a viewer expected color;

if a pixel color is determined to correspond to said viewer expected color, altering said pixel color to better approximate said viewer expected color.

2. The method of claim 1, wherein:

said viewer expected color is a skin tone; and

said step of determining whether said pixel color is within said range of predetermined colors corresponding to a viewer expected color includes discounting an illuminant of said pixel color.

3. The method of claim 2, further comprising:

converting said pixel color of each pixel from an input color format to a Jhs color format; and

said step of discounting an illuminant of said pixel color includes determining whether said pixel color is within said range of predetermined colors correspond to a viewer expected color using only saturation s and hue h of said pixel color.

4. The method of claim 1, wherein:

said at least one range of predetermined colors corresponding to a viewer expected color includes a probability distribution function of colors corresponding to skin tone.

5. The method of claim 1, wherein:

said at least one range of predetermined colors corresponding to a viewer expected color includes a probability distribution function of colors corresponding to grass green.

6. The method of claim 1, wherein:

said at least one range of predetermined colors corresponding to a viewer expected color includes a probability distribution function of colors corresponding to sky blue.

7. The method of claim 1, wherein:

said at least one range of predetermined colors corresponding to a viewer expected color includes a first probability distribution function of colors corresponding to skin tone, a second probability distribution function of colors corresponding to grass green and a third probability distribution function corresponding to sky blue.

8. The method of claim 1, further comprising:

if a pixel color is determined to correspond to said viewer expected color, altering the saturation s of said corresponding pixel.

9. The method of claim 8, wherein:

said at least one range of predetermined colors corresponding to a viewer expected color includes a probability distribution function of colors corresponding to skin tone; and

said step of altering the saturation s of said corresponding pixel includes reducing said saturation s of said corresponding pixel.

10. The method of claim 8, wherein:

said at least one range of predetermined colors corresponding to a viewer expected color includes a probability distribution function of colors corresponding to grass green; and

said step of altering the saturation s of said corresponding pixel includes boosting said saturation s of said corresponding pixel.

11. The method of claim 8, wherein:

said at least one range of predetermined colors corresponding to a viewer expected color includes a probability distribution function of colors corresponding to sky blue; and

said step of altering the saturation s of said corresponding pixel includes boosting said saturation s of said corresponding pixel.

12. The method of claim 8, wherein:

said at least one range of predetermined colors corresponding to a viewer expected color includes a first probability distribution function of colors corresponding to skin tone, a second probability distribution function of colors corresponding to grass green and a third probability distribution function corresponding to sky blue;

said step of altering the saturation s of said corresponding pixel includes reducing said saturation s of said corresponding pixel determined to be within said first probability distribution function;

said step of altering the saturation s of said corresponding pixel includes boosting said saturation s of said corresponding pixel determined to be within said second probability distribution function; and

said step of altering the saturation s of said corresponding pixel includes boosting said saturation s of said corresponding pixel determined to be within said third probability distribution function.

13. The method of claim 8, further comprising:

determining if a pixel is dark; and

if a pixel color is determined be dark, reducing said saturation s of said corresponding pixel.

14. The method of claim 8, further comprising:

determining if a pixel has low color; and

if a pixel color is determined be have low color, reducing said saturation s of said corresponding pixel.

15. The method of claim 1, further comprising:

converting said pixel color of each pixel from an input color format to a Jhs color format;

determining for each pixel a maximum saturation s for the corresponding lightness J and hue h;

selecting an output saturation s equal to the minimum of an input saturation s and said maximum saturation s.

16. The method of claim 15, further comprising:

converting said pixel color of each pixel from said Jhs color format employing said output saturation s into an RGB color format; and

said step of determining for each pixel a maximum saturation s determines a saturation s which when coupled with lightness J and hue h of said pixel enables conversion to said RBG color format within an allowable range of said RGB color format.