PERCEPTUAL COLOR TRANSFORMATIONS FOR WIDE COLOR GAMUT VIDEO CODING

• US 20160323556A1
• Filed: 09/22/2015
• Published: 11/03/2016
• Est. Priority Date: 05/01/2015
• Status: Active Grant

• Current Assignee: Eidgenoessische Technische Hochschule Zurich, Disney Enterprises Incorporated (The Walt Disney Company)
• Original Assignee: Eidgenoessische Technische Hochschule Zurich, Disney Enterprises Incorporated (The Walt Disney Company)
• Inventors: LUGINBUHL, DANIEL, SMOLIC, ALJOSA, STEFANOSKI, NIKOLCE, AYDIN, TUNC OZAN
• Granted Patent: US 10,257,526 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06T 5/90 Dynamic range modification of images or parts thereof
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/85 using pre-processing or post-processing specially adapted for video compression
• CPC Class Codes: H04N 9/67 for matrixing camera processing pipelines for matrixing of colour signals H04N23/85

Abstract

A video coding pipeline is provided that can accommodate high dynamic range (HDR) and wide color gamut (WCG) content at a fixed bitrate. The video coding pipeline relies on separate chromaticity and luminance-specific transforms in order to process image content. Image content may be converted into a nearly perceptually uniform color space for coding in constant luminance. Moreover, chromaticity transforms are utilized which reduce coding errors in the chroma components (at the fixed bitrate) by enlarging the distribution of code words for compression.

Claims

1. A computer-implemented method, comprising:

converting an additive color model signal into a uniform color space signal having chromaticity components and a luminance component;

transforming the chromaticity components and the luminance component by applying a chromaticity-specific transform to the chromaticity components and applying a luminance-specific transform to the luminance component;

quantizing the transformed chromaticity components and luminance component; and

encoding the quantized chromaticity components and luminance component.

2. The computer-implemented method of claim 1, wherein the additive color model signal comprises a red-green-blue (RGB) color model signal.

3. The computer-implemented method of claim 1, wherein the uniform color space signal comprises a YUV color space signal.

4. The computer-implemented method of claim 3, wherein the transformation of the chromaticity components comprises subdividing a main triangular representation of the chromaticity components in the YUV color space into a mesh comprising a plurality of secondary triangles.

5. The computer-implemented method of claim 4, wherein each of the vertices of the main triangular representation comprises one of the primaries of the additive color model.

6. The computer-implemented method of claim 5, further comprising defining a midway vertex between two of the primaries of the additive color model.

7. The computer-implemented method of claim 6, further comprising mapping each of the vertices of the main triangular representation and the defined midway vertex to a rectangular representation of the chromaticity components in the YUV color space.

8. The computer-implemented method of claim 7, wherein the rectangular representation comprises a unit square.

9. The computer-implemented method of claim 7, wherein respective vertices of each of the plurality of secondary triangles is mapped to the rectangular representation of the chromaticity components in the YUV color space using mean value coordinates.

10. The computer-implemented method of claim 9, wherein values of each of the chromaticity components in the YUV color space are mapped to the rectangular representation thereof using barycentric coordinates corresponding to the values of each of the chromaticity components.

11. The computer-implemented method of claim 6, further comprising mapping each of the vertices of the main triangular representation and the defined midway vertex to a four-sided polygonal representation of the chromaticity components in the YUV color space.

12. The computer-implemented method of claim 11, further comprising applying at least one of a plurality of constraints affecting the mapping of each of the vertices of the main triangular representation, each of the vertices of each of the plurality of secondary triangles, and the defined midway vertex to the four-sided polygonal representation.

13. The computer-implemented method of claim 12, further comprising adjusting characteristics of at least one of the plurality of constraints to modify the chromaticity-specific transform.

14. The computer-implemented method of claim 1, wherein the luminance-specific transform comprises an opto-electrical transfer function.

15. A non-transitory computer readable medium having computer executable program code embodied thereon, the computer executable program code configured to cause a processor to:

decode quantized color and brightness components of an input bitstream carrying an image signal represented by a first color space model having brightness and color components;

dequantize the quantized color and brightness components;

apply a first inverse transform to the dequantized color component;

apply a second inverse transform to the dequantized brightness component; and

convert the image signal represented by a first color space model into that represented by a second color space model, the second color space model being an additive color space model.

16. The non-transitory computer readable medium of claim 15, wherein the first inverse transform comprises one of an inverse direct transform or an inverse least squares transform, wherein the color and brightness components have been previously transformed to increase the number of code words available to a video codec for compressing the image signal.

17. The non-transitory computer readable medium of claim 16, wherein the first color space model comprises a YUV color space model, the second color space model comprises a a red-green-blue (RGB) color space model, and the video codec comprises a high efficiency video coding (HEVC) codec.

18. The non-transitory computer readable medium of claim 15, wherein the image signal comprises one of a standard dynamic range (SDR) image signal, a high dynamic range (HDR) image signal, a standard color gamut (SCG) image signal, or a wide color gamut (WCG) image signal.

19. A system, comprising:

a converter to convert an image signal represented by a first color space model into that represented by a second color space model having brightness and color components;

a first transformer to apply a first transform to the color component;

an opto-electrical transfer function encoder to apply a second transform to the brightness component;

a quantizer to quantize the transformed color and brightness components; and

an encoder to encode the quantized color and brightness components and output a bitstream.

20. The system of claim 19, wherein the first transform is invertible.