Method and device for decoding a color picture

• US 10,455,245 B2
• Filed: 01/27/2016
• Issued: 10/22/2019
• Est. Priority Date: 01/30/2015
• Status: Active Grant

• Current Assignee: Interdigital Vc Holdings, Inc. (InterDigital, Inc.)
• Original Assignee: Interdigital Vc Holdings, Inc. (InterDigital, Inc.)
• Inventors: Lasserre, Sebastien, Leleannec, Fabrice, Olivier, Yannick
• Primary Examiner(s): Entezari, Michelle M
• Application Number:
  US15/546,336
• Publication Number:
  US 20180027252A1
• Time in Patent Office: 1,364 Days
• Field of Search: None
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/136 Incoming video signal characteristics or properties
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/30 using hierarchical techniques, e.g. scalability H04N19/63 takes precedence
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• CPC Class Codes: H04N 19/98 Adaptive-dynamic-range coding [ADRC]

Abstract

The present disclosure generally relates to a device and a method of decoding a color picture from a bitstream. It comprises: —obtaining an expanded range luminance as a first component by applying a nonlinear dynamic expansion function to a luminance component obtained from the bitstream, wherein said nonlinear dynamic expansion function is determined depending on an inverse of a dynamic reduction function that has been applied to an original luminance component obtained when encoding the color picture; —obtaining a second component by calculating a square root of a difference between a value determined by the first component and another value computed as a linear combination of a multiplication product of two chrominance components and square values of the two chrominance components obtained from the bitstream; and —obtaining at least one color component of the color picture to be decoded at least from said second component and said two chrominance components by determining said at least one color component as a linear combination of the second component and the two chrominance components.

Claims

1. A method of decoding a color picture from a bitstream, comprising:

obtaining a final luminance component by linear combining a luminance and chrominance components obtained from a bitstream;

obtaining a first component by applying a non-linear dynamic expansion function on said final luminance component in order that the dynamic of the first component is increased compared to the dynamic of the final luminance component;

obtaining a normalized multiplicative factor by dividing a multiplicative factor obtained from the bitstream by the square root of the first component;

recovering at least one color component of the color picture to be decoded from said chrominance components and said first component by;

obtaining intermediate chrominance components by multiplying the chrominance components by said normalized multiplicative factor;

obtaining at least one intermediate color component from the squares of said two intermediate chrominance components, the product of said two intermediate chrominance components and a color transform matrix; and

obtaining at least one color component of the decoded color picture from the first component and one of said at least one intermediate color component.

2. The method of claim 1, wherein said at least one intermediate color component is obtained by:

obtaining a second component by calculating a square root of a weighted linear combination of at least the squares of said two intermediate chrominance components and the product of said two intermediate chrominance components; and

said at least one intermediate color component is obtained by multiplying said second component and said two intermediate chrominance components, by said color transform matrix.

3. The method of claim 1, wherein said at least one intermediate color component is obtained by:

calculating a weighted linear combination of the squares of said two intermediate chrominance components and the product of said two intermediate chrominance components;

checking whether or not weighted linear combination is a positive or null value;

if so,

obtaining a second component by calculating a square root of sum of the unity value with said weighted linear combination; and

said at least one intermediate color component is obtained by multiplying said second component and said two intermediate chrominance components, by said color transform matrix;

otherwise,

setting a second component to the null value;

dividing said two intermediate chrominance components by the square root of said weighted linear combination; and

said at least one intermediate color component is obtained by multiplying said second component and said two intermediate chrominance components once divided, by said color transform matrix.

4. The method of claim 1, wherein said nonlinear dynamic expansion function is an inverse of a dynamic reduction function that has been applied to an original luminance component obtained when encoding the color picture.

5. The method of claim 1, wherein said normalized multiplicative factor also depends on a backlight value obtained from the original luminance component.

6. The method of claim 2, wherein the second component is determined using a look up table.

13. A computer program product comprising program code instructions to execute the steps of the method according to claim 1 when this program is executed on a computer.

14. A processor readable medium having stored therein instructions for causing a processor to perform at least the steps of the method according to claim 1.

15. A non-transitory storage medium carrying instructions of program code for executing steps of the method according to claim 1, when said program is executed on a computing device.

7. A device of decoding a color picture from a bitstream, comprising a processor configured to:

obtain a final luminance component by linear combining a luminance and chrominance components obtained from a bitstream;

obtain a first component by applying a non-linear dynamic expansion function on said final luminance component in order that the dynamic of the first component is increased compared to the dynamic of the final luminance component;

obtain a normalized multiplicative factor by dividing a multiplicative factor obtained from the bitstream by the square root of the first component;

recover at least one color component of the color picture to be decoded from said chrominance components and said first component by;

obtaining intermediate chrominance components from the chrominance components and said normalized multiplicative factor;

obtaining at least one intermediate color component from said two intermediate chrominance components, the product of said two intermediate chrominance components and a color transform matrix; and

obtaining at least one color component of the decoded color picture from the first component and one of said at least one intermediate color component.

8. The device of claim 7, wherein said at least one intermediate color component is obtained by:

obtaining a second component by calculating a square root of a weighted linear combination of at least the squares of said two intermediate chrominance components and the product of said two intermediate chrominance components; and

said at least one intermediate color component is obtained by multiplying said second component and said two intermediate chrominance components, by said color transform matrix.

9. The device of claim 7, wherein said at least one intermediate color component is obtained by:

calculating a weighted linear combination of the squares of said two intermediate chrominance components and the product of said two intermediate chrominance components;

checking whether or not weighted linear combination is a positive or null value;

if so,

obtaining a second component by calculating a square root of sum of the unity value with said weighted linear combination; and

said at least one intermediate color component is obtained by multiplying said second component and said two intermediate chrominance components, by said color transform matrix;

otherwise,

setting a second component to the null value;

dividing said two intermediate chrominance components by the square root of said weighted linear combination; and

said at least one intermediate color component is obtained by multiplying said second component and said two intermediate chrominance components once divided, by said color transform matrix.

10. The device of claim 7, wherein said nonlinear dynamic expansion function is an inverse of a dynamic reduction function that has been applied to an original luminance component obtained when encoding the color picture.

11. The device of claim 7, wherein said normalized multiplicative factor also depends on a backlight value obtained from the original luminance component.

12. The device of claim 8, wherein the second component is determined using a look up table.