Method and apparatus of intra mode coding

Patent metadata

Field	Value
Publication number	US-10070126-B2
Application number	US-201214123201-A
Country	US
Kind code	B2
Filing date	Apr 18, 2012
Priority date	Jun 28, 2011
Publication date	Sep 4, 2018
Grant date	Sep 4, 2018

Abstract

Method and apparatus for intra prediction mode coding and decoding are disclosed. In one embodiment, the encoding and decoding process assigns individual indices and codewords to DC mode and Planar mode respectively. The flag is set if the current intra prediction mode is equal to any of one or more neighboring intra prediction modes. Variable length codes are designed for a remaining mode set. If the flag is not set, the currently intra prediction mode is encoded using the variable length codes. In another embodiment, multiple most probable modes are used. If the current intra prediction mode is not equal to any of the multiple most probable modes, the current intra prediction mode is encoded using variable length codes designed for the corresponding remaining modes according the ranking order of the remaining modes.

First claim

The invention claimed is:

1. A method of decoding a block, the method comprising:
receiving a flag indicating whether a current intra prediction mode is equal to any of one or more most probable modes;
deriving, by a processor of a decoding apparatus based on a value of the flag, the current intra prediction mode from a decoded mode index by applying a context-adaptive entropy decoding process associated with variable length coding or arithmetic coding; and
decoding, by the processor of the decoding apparatus, the block according to the current intra prediction mode identified by the decoded mode index,
wherein
the current intra prediction mode belongs to a mode set that comprises a DC mode, a Planar mode, and at least one directional mode, each mode of the mode set being represented by a different mode index value,
the deriving the current intra prediction mode from the decoded mode index comprises:
when the decoded mode index corresponds to a first mode index value that represents the DC mode, deriving the current intra prediction mode to be the DC mode; and
when the decoded mode index corresponds to a second mode index value that represents the Planar mode, deriving the current intra prediction mode to be the Planar mode,
the first mode index value is first in a predetermined order among mode index values of modes of the mode set, and
the second mode index value is second in the predetermined order among the mode index values of the modes of the mode set.

2. The method of claim 1 , wherein
the mode set further comprising a Vertical mode and a Horizontal mode, and
the DC mode, the Planar mode, the Vertical mode, and the Horizontal mode are mapped into any permutation of a mode index group consisting of mode index values including 0, 1, 2, and 3.

3. The method of claim 1 , further comprising, if the flag indicates that the current intra prediction mode is not equal to any of the one or more most probable modes, determining a remaining mode set consisting of the intra prediction modes of the mode set that are not equal to any of the one or more most probable modes,
wherein the variable length coding is designed based on the mode index values and a ranking order of the remaining mode set.

4. The method of claim 3 , wherein
the variable length coding is based on a first table or a second table,
the first table is selected when two neighboring intra prediction modes of two neighboring blocks of the block are equal, and
the second table is selected when the two neighboring intra prediction modes are not equal.

5. The method of claim 4 , wherein
the first table comprises code lengths associated with seventeen intra prediction modes of the remaining mode set and the flag for 4×4 block size, and
the code lengths are {4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 1} for the seventeen intra prediction modes and the flag.

6. The method of claim 4 , wherein
the second table comprises code lengths associated with sixteen intra prediction modes of the remaining mode set and the flag for 4×4 block size, and
the code lengths are {4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 1} for the sixteen intra prediction modes and the flag.

7. The method of claim 4 , wherein
the first table comprises code lengths associated with seventeen intra prediction modes of the remaining mode set for 4×4 block size,
the code lengths are {3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5} for the seventeen intra prediction modes, and
the first table does not include the flag.

8. The method of claim 4 , wherein
the second table comprises code lengths associated with sixteen intra prediction modes of the remaining mode set for 4×4 block size,
the code lengths are {3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5 5, 5} for the sixteen intra prediction modes, and
the second table does not include the flag.

9. The method of claim 4 , wherein
the first table comprises code lengths associated with 34 intra prediction modes of the remaining mode set and the flag for 32×32, 16×16, and 8×8 block sizes, and
the code lengths are {4, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7. 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 1} for the 34 intra prediction modes and the flag.

10. The method of claim 4 , wherein the second table comprises code lengths associated with 33 intra prediction modes of the remaining mode set and the flag for 32×32, 16×16, and 8×8 block sizes, and
the code lengths are {4, 4, 5, 6, 6, 6 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7 7 7, 7 7 7,7, 7, 7, 7, 7, 7, 8, 8, 1}for the 33 intra prediction modes and the flag.

11. The method of claim 4 , wherein
the first table comprises code lengths associated with 34 intra prediction modes of the remaining mode set for 32×32, 16×16, and 8×8 block sizes,
the code lengths are {3, 4, 4, 4, 5, 5 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7} for the 34 intra prediction modes, and
the first table does not include the flag.

12. The method of claim 4 , wherein
the second table comprises code lengths associated with 33 intra prediction modes of the remaining mode set for 32×32, 16×16, and 8×8 block sizes,
the code lengths are {3, 3, 4, 5, 5, 5, 5, 5, 5, 5 5, 5, 5, 5, 5, 5, 5, 5 6, 6, 6, 6, 6, 6, 6, 6, 6 6, 6, 6, 6, 7, 7} for the 33 intra prediction modes, and
the second table does not include the flag.

13. The method of claim 3 , wherein
the variable length coding is based on a first table or second table,
the first table is selected when the flag is coded using variable length code table, and
the second table is selected when the flag is coded separately.

14. An apparatus of decoding a block, the apparatus comprising:
a processor configured to execute executable code to cause the processor to:
receive a flag indicating whether a current intra prediction mode is equal to one or more most probable modes;
derive, based on a value of the flag, the current intra prediction mode from a decoded mode index by applying a context-adaptive entropy decoding process associated with variable length coding or arithmetic coding; and
decode the block according to the current intra prediction mode identified by the decoded mode index,
wherein
the current intra prediction mode belongs to a mode set that comprises a DC mode, a Planar mode, and at least one directional mode, each mode of the mode set being represented by a different mode index value,
the processor is configured to:
when the decoded mode index corresponds to a first mode index value that represents the DC mode, derive the current intra prediction mode to be the DC mode; and
when the decoded mode index corresponds to a second mode index value that represents the Planar mode, derive the current intra prediction mode to be the Planar mode,
the first mode index value is first in a predetermined order among mode index values of modes of the mode set, and
the second mode index value is second in the predetermined order among the mode index values of the modes of the mode set.

15. A method of encoding a block, the method comprising:
receiving a current intra prediction mode corresponding to the block, the current intra prediction mode belonging to a mode set that comprises a DC mode, a Planar mode, and at least one directional mode, each mode of the mode set being represented by a different mode index value;
mapping, by a processor of an encoding apparatus, the current intra prediction mode into a mode index based on a corresponding mode index value that represents the current intra prediction mode;
including a flag indicating whether the current intra

Assignees

• Guo Mei
• Guo Xun
• Lei Shaw Min
• Hfi Innovation Inc

Inventors

• Guo Mei
• Guo Xun
• Lei Shaw-Min

Classifications

• H04N19/176

  the region being a block, e.g. a macroblock · CPC title

• H04N19/157

  Assigned coding mode, i.e. the coding mode being predefined or preselected to be further used for selection of another element or parameter · CPC title

• H04N19/593

  involving spatial prediction techniques · CPC title

• H04N19/105 Primary

  Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction · CPC title

• H04N19/11

  among a plurality of spatial predictive coding modes · CPC title