Advanced arithmetic coder

Patent metadata

Field	Value
Publication number	US-2016353108-A1
Application number	US-201615166068-A
Country	US
Kind code	A1
Filing date	May 26, 2016
Priority date	May 29, 2015
Publication date	Dec 1, 2016
Grant date	—

Abstract

An example method of entropy coding video data includes obtaining a pre-defined initialization value for a context of a plurality of contexts used in a context-adaptive entropy coding process to entropy code a value for a syntax element in a slice of the video data, wherein the pre-defined initialization value is stored with N-bit precision; determining, using a look-up table and based on the pre-defined initialization value, an initial probability state of the context for the slice of the video data, wherein a number of possible probability states for the context is greater than two raised to the power of N; and entropy coding, based on the initial probability state of the context, a bin of the value for the syntax element.

First claim

What is claimed is:

1 . A method of entropy coding video data, the method comprising:
obtaining a pre-defined initialization value for a context of a plurality of contexts used in a context-adaptive entropy coding process to entropy code a value for a syntax element in a slice of the video data, wherein the pre-defined initialization value is stored with N-bit precision; determining, based on the pre-defined initialization value, an initial probability state of the context for the slice of the video data, wherein a number of possible probability states for the context is greater than two raised to the power of N; and entropy coding, based on the initial probability state of the context, a bin of the value for the syntax element.

2 . The method of claim 1 , further comprising:
determining, based on the pre-defined initialization value, a slope value and an offset value, wherein determining the initial probability state comprises:
determining an intermediate value based on the slope value, the offset value, and a quantization parameter of the slice of the video data; and
mapping, using a look-up table, the intermediate value to the initial probability state.

3 . The method of claim 2 , wherein the look-up table includes a number of entries that is less than or equal to two raised to the power of N.

4 . The method of claim 3 , wherein the number of entries is equal to a number of possible values of the intermediate value.

5 . The method of claim 1 , wherein determining the initial probability state of the context comprises determining the initial probability state of the context using a look-up table, and wherein values in the look-up table are defined in accordance with the following equation:
MappedProb[ i ]=Ceil(2 M *prob[ i ]+offset) where MappedProb[i] is the ith value in the look up table, prob[i] represents the ith value in a table that represents a set of possible probabilities of a one symbol, two raised to the power of M represents the number of possible probability states for the context, and Ceil(x) is a function that denotes the smallest integer greater than or equal to x.

6 . The method of claim 5 , wherein prob[i] represents an ith possible probability of a 1 symbol.

7 . The method of claim 5 , wherein the number of possible probability states for the context is greater than or equal to two raised to the power of N.

8 . The method of claim 5 , wherein N is eight and the number of possible probability states for the context is two raised to the power of 15.

9 . The method of claim 5 , wherein offset is equal to 0.5 or 0.

10 . The method of claim 1 , further comprising:
determining, based on the pre-defined initialization value, a slope value and an offset value, wherein determining the initial probability state comprises:
determining an intermediate value based on the slope value, the offset value, and a quantization parameter of the slice of the video data; and
determining, using a mapping function between intermediate values and initial probability states, the initial probability state based on the intermediate value.

11 . The method of claim 1 , wherein entropy coding comprises entropy encoding the bin.

12 . The method of claim 1 , wherein entropy coding comprises entropy decoding the bin.

13 . The method of claim 1 , wherein the context-adaptive entropy coding process comprises a context-adaptive binary arithmetic coding (CABAC) process, or a context-adaptive variable length coding (CAVLC) process.

14 . An apparatus for entropy coding of video data, the apparatus comprising:
a memory configured to store a plurality of contexts used in a context-adaptive entropy coding process to entropy code a value for a syntax element in a slice of the video data; and one or more processors configured to:
obtain a pre-defined initialization value for a context of the plurality of contexts, wherein the pre-defined initialization value is stored with N-bit precision;
determine, based on the pre-defined initialization value, an initial probability state of the context for the slice of the video data, wherein a number of possible probability states for the context is greater than two raised to the power of N; and
entropy code, based on the initial probability state of the context, a bin of the value for the syntax element

15 . The apparatus of claim 14 , wherein the one or more processors are further configured to:
determine, based on the pre-defined initialization value, a slope value and an offset value, wherein, to determine the initial probability state, the one or more processors are configured to:
determine an intermediate value based on the slope value, the offset value, and a quantization parameter of the slice of the video data; and
map, using a look-up table, the intermediate value to the initial probability state.

16 . The apparatus of claim 15 , wherein the look-up table includes a number of entries that is less than or equal to two raised to the power of N.

17 . The apparatus of claim 16 , wherein the number of entries is equal to a number of possible values of the intermediate value.

18 . The apparatus of claim 14 , wherein, to determine the initial probability state of the context, the one or more processors are configured to use a look-up table, and wherein values in the look-up table are defined in accordance with the following equation:
MappedProb[ i ]=Ceil(2 M *prob[ i ]+offset) where MappedProb[i] is the ith value in the look up table, prob[i] represents the ith value in a table that represents a set of possible probabilities of a one symbol, two raised to the power of M represents the number of possible probability states for the context, and Ceil(x) is a function that denotes the smallest integer greater than or equal to x.

19 . The apparatus of claim 18 , wherein prob[i] represents an ith possible probability of a 1 symbol.

20 . The apparatus of claim 18 , wherein the number of possible probability states for the context is greater than or equal to two raised to the power of N.

21 . The apparatus of claim 18 , wherein N is eight and the number of possible probability states for the context is two raised to the power of 15.

22 . The apparatus of claim 18 , wherein offset is equal to 0.5 or 0.

23 . The apparatus of claim 14 , wherein the one or more processors are further configured to:
determine, based on the pre-defined initialization value, a slope value and an offset value, wherein, to determine the initial probability state, the one or more processors are configured to:
determine an intermediate value based on the slope value, the offset value, and a quantization parameter of the slice of the video data; and
determine, using a mapping function between intermediate values and initial probability states, the initial probability state based on the intermediate value.

24 . The apparatus of claim 14 , wherein, to entropy code, the one or more processors are configured to entropy encode the bin.

25 . The apparatus of claim 14 , wherein, to entropy code, the one or more processors are configured to entropy decode the bin.

26 . The apparatus of claim 14 , wherein the context-adaptive entropy coding process comprises a context-adaptive binary arithmetic coding (CABAC) process, or a context-adaptive variable length coding (CAVLC) process.

27 . The apparatus of claim 14 ,

Assignees

• Qualcomm Inc

Inventors

• Zhang Li
• Chen Jianle
• Zhao Xin
• Li Xiang
• Liu Hongbin
• Chen Ying
• Karczewicz Marta

Classifications

• H04N19/42

  characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation (H04N19/635 takes precedence) · CPC title

• H04N19/70

  characterised by syntax aspects related to video coding, e.g. related to compression standards · CPC title

• H04N19/174

  the region being a slice, e.g. a line of blocks or a group of blocks · CPC title

• H04N19/139

  Analysis of motion vectors, e.g. their magnitude, direction, variance or reliability · CPC title

• H04N19/184

  the unit being bits, e.g. of the compressed video stream · CPC title