Method and Apparatus for Entropy Coding of Source Samples with Large Alphabet

• US 20180302626A1
• Filed: 06/26/2018
• Published: 10/18/2018
• Est. Priority Date: 01/30/2015
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: HSIANG, Shih-Ta
• Granted Patent: US 10,819,981 B2
• Time in Patent Office: Days
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• CPC Class Codes: H04N 19/139 Analysis of motion vectors, e.g. their magnitude, direction, variance or reliability
• CPC Class Codes: H04N 19/184 the unit being bits, e.g. of the compressed video stream
• CPC Class Codes: H04N 19/1887 the unit being a variable length codeword
• CPC Class Codes: H04N 19/52 by predictive encoding
• CPC Class Codes: H04N 19/70 characterised by syntax aspects related to video coding, e.g. related to compression standards
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

A method of entropy coding for source symbols in an encoder receives a current source symbol having a current symbol value belonging to a set of symbol values. When the source symbols correspond to horizontal components or vertical components of motion vector differences (MVDs) for Inter prediction coding, the method determines a threshold for the set of symbol values. If an absolute current symbol value is greater than the threshold associated with a corresponding motion vector resolution for the current source symbol, the method derives a first binary string. If the absolute current symbol value is not greater than the threshold associated with the corresponding motion vector resolution for the current source symbol, the method derives a second binary string. Finally, the method encodes the first binary string or the second binary string depending on whether the absolute current symbol value is greater than the threshold.

Claims

1. A method of entropy coding for source symbols in an encoder comprising:

receiving a current source symbol having a current symbol value belonging to a set of symbol values;

when the source symbols correspond to horizontal components or vertical components of motion vector differences (MVDs) for Inter prediction coding, determining a threshold for the set of symbol values, wherein separate thresholds are selected for the source symbols corresponding to different motion vector resolutions related to the MVDs;

if an absolute current symbol value is greater than the threshold associated with a corresponding motion vector resolution for the current source symbol, deriving a first binary string by binarizing a remaining absolute level of the absolute current symbol value using a variable length code;

if the absolute current symbol value is not greater than the threshold associated with the corresponding motion vector resolution for the current source symbol, deriving a second binary string by binarizing the remaining absolute level of the absolute current symbol value using a fixed-length code; and

encoding the first binary string or the second binary string depending on whether the absolute current symbol value is greater than the threshold.

2. The method of claim 1, wherein when the source symbols correspond to the horizontal components or the vertical components of block vector differences (BVDs) for Intra block copy (IBC), Intra line copy or Intra string copy (ISC) coding, or the horizontal components or the vertical components of the MVDs for the Inter prediction coding, separate thresholds are selected for the source symbols corresponding to different components of the BVDs or the MVDs.

3. The method of claim 1, wherein the threshold is signaled in SPS (Sequence Parameter Set), PPS (Picture Parameter Set), or slice header of a bitstream.

4. A method of entropy decoding for source symbols in a decoder comprising:

receiving an input coded bitstream including compressed data for a current source symbol, wherein the source symbols are associated with horizontal components or vertical components of motion vector differences (MVDs) for Inter prediction coding;

determining a threshold for a set of symbol values depending on motion vector resolution related to the MVDs;

parsing the input coded bitstream to determine whether a first binary string or a second binary string is received, wherein the first binary string corresponds to a remaining absolute level when an absolute current symbol value for a current source symbol is greater than the threshold and the second binary string corresponds to the remaining absolute level when the absolute current symbol value is not greater than the threshold, and wherein the threshold is associated with a corresponding motion vector resolution for the current source symbol;

if the first binary string is received, recovering the remaining absolute level using a variable length code;

if the second binary string is received, recovering the remaining absolute level using a fixed-length code; and

decoding the absolute current symbol value based on the remaining absolute level and the threshold if the first string is received or based on the remaining absolute level if the second string is received.

5. The method of claim 4, wherein information regarding the threshold is parsed from SPS (Sequence Parameter Set), PPS (Picture Parameter Set), or slice header of a bitstream.

6. A method of entropy coding for source symbols in an encoder comprising:

receiving a current source symbol belonging to a set of source symbols, wherein each source symbol consists of a horizontal component and a vertical component, and the horizontal component and the vertical component are associated with one motion vector difference (MVD) for Inter prediction coding, or one block vector difference (BVD) for Intra block copy (IBC), Intra line copy, or one vector offset for Intra string copy (ISC) coding, or one position vector for the last significant coefficient in a transform unit (TU);

determining a first flag indicating whether a first absolute value of a first component is greater than zero, wherein the first component corresponds to the horizontal component or the vertical component;

determining a second flag indicating whether a second absolute value of a second component is greater than zero, wherein the second component corresponds to the horizontal component or the vertical component and is a different component from the first component; and

encoding the second flag using context model derived based on the first flag after the first flag is coded, or encoding a pair of the first flag and the second flag jointly.

7. The method of claim 6, wherein when the pair of the first flag and the second flag is encoded jointly, the pair of the first flag and the second flag is binarized into a bin string using a truncated unary code with a maximum value equal to 3.

8. The method of claim 7, wherein the bin string is coded in a CABAC (context-adaptive binary arithmetic coding) mode with context selection determined by a bin index.

9. The method of claim 6, wherein when the horizontal component and the vertical component are associated with one offset vector Intra string copy (ISC) coding, and the pair of the first flag and the second flag is encoded jointly, a combination for both the first flag and the second flag being zero is excluded from encoding process and the pair of the first flag and the second flag is binarized into a bin string using a truncated unary code with a maximum value equal to 2.

10. A method of entropy decoding for source symbols in an decoder comprising:

receiving an input coded bitstream including compressed data for a current source symbol belonging to a set of source symbols, wherein each source symbol consists of a horizontal component and a vertical component, and the horizontal component and the vertical component are associated with one motion vector difference (MVD) for Inter prediction coding, or one block vector difference (BVD) for Intra block copy (IBC), Intra line copy or one vector offset for Intra string copy (ISC) coding, or one position vector for the last significant coefficient in a TU;

decoding a second flag using context model derived based on a first flag after the first flag is decoded, or decoding a pair of the first flag and the second flag jointly, wherein the first flag indicating whether a first absolute value of a first component is greater than zero and the second flag indicating whether a second absolute value of a second component is greater than zero, and wherein the first component corresponds to the horizontal component or the vertical component and the second component corresponds to the horizontal component or the vertical component and is a different component from the first component; and

recovering the horizontal component and the vertical component using decoded information including the first flag and the second flag.

11. A method of entropy coding for source symbols in an encoder comprising:

receiving a current source symbol belonging to a set of source symbols, wherein each source symbol consists of a horizontal component and a vertical component associated with one offset vector for Intra line copy or Intra string copy (ISC) coding;

signaling one or more first syntax elements for indicating whether a first absolute value corresponding to the horizontal component is greater than zero and a second absolute value corresponding to the vertical component is greater than zero; and

signaling one or more second syntax elements only if said one or more first syntax elements indicate the first absolute value being greater than zero and the second absolute value being greater than zero, wherein said one or more second syntax elements represent a sign part of the horizontal component and a sign part of the vertical component.

12. The method of claim 11, wherein when the sign part of the horizontal component or the sign part of the vertical component is not signaled, the sign part of the horizontal component or the sign part of the vertical component is inferred to be positive respectively.

13. The method of claim 11, wherein said one or more second syntax elements correspond to one new syntax representing a pair of the sign part of the horizontal component or the sign part of the vertical component, and the new syntax is binarized into a bin string by a truncated unary code with a maximum value equal to 2.

14. The method of claim 13, wherein the bin string is coded in a CABAC (context-adaptive binary arithmetic coding) mode or a bypass mode.

15. The method of claim 11, wherein a combination for both the sign part of the horizontal component or the sign part of the vertical component being zero is excluded from encoding process for the sign part of the horizontal component or the sign part of the vertical component.

16. A method of entropy decoding for source symbols in an decoder comprising:

receiving an input coded bitstream including compressed data for a current source symbol belonging to a set of source symbols, wherein each source symbol consists of a horizontal component and a vertical component associated with one offset vector for Intra line copy or Intra string copy (ISC) coding;

parsing one or more first syntax elements indicating whether a first absolute value corresponding to the horizontal component is greater than zero and whether a second absolute value corresponding to the vertical component is greater than zero; and

if said one or more first syntax elements indicate the first absolute value being greater than zero and the second absolute value being greater than zero;

parsing one or more second syntax elements representing a sign part of the horizontal component and a sign part of the vertical component; and

recovering the horizontal component and the vertical component using decoded information including the sign part of the horizontal component and the sign part of the vertical component.

17. The method of claim 16, wherein when the sign part of the horizontal component or the sign part of the vertical component is not signaled, the sign part of the horizontal component or the sign part of the vertical component is inferred to be positive respectively.