Encoding and decoding perceptually-quantized video content

Patent metadata

Field	Value
Publication number	US-9936199-B2
Application number	US-201515513928-A
Country	US
Kind code	B2
Filing date	Sep 24, 2015
Priority date	Sep 26, 2014
Publication date	Apr 3, 2018
Grant date	Apr 3, 2018

Abstract

Compared to traditional gamma-coded video, perceptually quantized video provides greater flexibility for the transmission and display management of high-dynamic range video, but it does not compresses as efficiently using existing standard codecs. Techniques are described to improve the coding efficiency of perceptually coded video by applying a color cross-talk transformation after the RGB/XYZ to LMS transformation. Such a transform increases luma and chroma correlation for color appearance models, but improves perceptual uniformity and overall coding efficiency for wide color gamut, HDR, signals.

First claim

What is claimed is:

1. A method to improve coding efficiency and perceptual uniformity for high dynamic range (HDR) video, the method comprising:
accessing a first video signal in a first color space; and
applying one or more color transformations to the first video signal to generate an output video signal in a perceptually-quantized opponent color space,
wherein applying one or more color transformations to the first video signal to generate the output video signal further comprises:
applying a first color transform to the first video signal to generate a second video signal in a linear primary color space;
applying a color cross-talk transformation matrix to the second video signal to generate a third video signal in the linear primary color space;
applying a perceptual quantizer to the third video signal to generate a fourth video signal in a perceptually quantized primary color space; and
applying a second color transform to the fourth video signal to generate the output video signal in the perceptually-quantized opponent color space.

2. The method of claim 1 , wherein the first color space is gamma-coded RGB (RGB gamma) or perceptually quantized RGB (RGB-PQ).

3. The method of claim 1 , further comprising:
applying a linearization function to the first video signal to generate a linearized first video signal and applying the first color transform to the linearized first video signal.

4. The method of claim 1 , wherein the perceptually quantized color space is generated according to the SMPTE specification ST 1084.

5. The method of claim 1 , wherein the linear primary color space is the LMS color space.

6. The method of claim 1 , wherein the perceptually-quantized opponent color space is the perceptually quantized IPT color space (IPT-PQ).

7. The method of claim 1 , wherein the color cross-talk transformation matrix comprises

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wherein c is a constant.

8. The method of claim 7 , wherein the value of c is determined as a function of the amount of valid code-words in the chroma components of the perceptually-quantized opponent color space.

9. The method of claim 8 , wherein the value of c is determined as the value for which the first derivative of E(c) is maximized, wherein E(c) denotes a function of valid code-words in the chroma components of the perceptually-quantized opponent color space as a function of c.

10. The method of claim 9 wherein the perceptually-quantized opponent color space comprises the IPT-PQ color space where P and T comprise the chroma components.

11. The method of claim 1 , further comprising applying a reshaping function to the output video signal to generate a reshaped output function and compressing the reshaped output function with a video encoder to generate a coded bit stream.

12. The method of claim 11 , wherein the reshaping function is non-linear for a luma component of the output video signal and linear for one or more chroma components of the output video signal.

13. The method of claim 12 , wherein the reshaping function for a chroma channel (P) of the output video signal comprises an input-output function given by:

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P

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Assignees

• Dolby Laboratories Licensing Corp

Inventors

• Froehlich Jan
• Atkins Robin
• Wang Qiuwei
• Su Guan-Ming
• Yin Peng

Classifications

• H04N9/67 Primary

  for matrixing (camera processing pipelines for matrixing of colour signals H04N23/85) · CPC title

• H04N19/186

  the unit being a colour or a chrominance component · CPC title

• H04N19/124 Primary

  Quantisation · CPC title

• H04N9/68

  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 title

• H04N19/85

  using pre-processing or post-processing specially adapted for video compression · CPC title