Coded block flag coding

Patent metadata

Field	Value
Publication number	US-9467701-B2
Application number	US-201313739598-A
Country	US
Kind code	B2
Filing date	Jan 11, 2013
Priority date	Apr 5, 2012
Publication date	Oct 11, 2016
Grant date	Oct 11, 2016

Abstract

A video encoder generates a bitstream that includes a residual quad tree (RQT) for a coding unit (CU). The CU is larger than a maximum-allowable transform unit (TU) size and the RQT includes a hierarchy of nodes. A root node of the RQT corresponds to the CU as a whole and leaf nodes of the RQT correspond to TUs of the CU. The root node is associated with a coded block flag (CBF) for a chroma component. The CBF for the chroma component indicates whether any of the TUs of the CU are associated with a significant coefficient block that is based on samples of the particular chroma component. A video decoder receives the bitstream and determines, based on the CBF, whether coefficient blocks associated with TUs that correspond to the leaf nodes include non-zero coefficients.

First claim

What is claimed is:

1. A method for encoding video data, the method comprising:
receiving or generating the video data, the video data representing a series of pictures;
generating a bitstream that includes a sequence of bits that forms an encoded representation of the video data, the bitstream including data that represent a residual quad tree (RQT) for a coding unit (CU) of a picture of the series of pictures, the CU being larger than a maximum-allowable transform unit (TU) size, the RQT including a hierarchy of nodes, wherein a root node of the RQT corresponds to the CU as a whole, each of the nodes of the RQT corresponds to a respective block, and respective leaf nodes of the RQT correspond to respective TUs of the CU, wherein generating bitstream comprises:
generating residual data for the CU based on predicted video blocks for one or more prediction units (PUs) of the CU and an original video block of the CU, wherein the residual data for the CU is partitioned into residual video blocks and each of the TUs of the CU is associated with a different one of the residual pixel blocks;
for each respective node of the RQT, responsive to determining a block corresponding to the respective node is larger than the maximum-allowable TU size, automatically splitting, without encoding in the bitstream a split flag for the respective node, the block corresponding to the respective node into four sub-blocks corresponding to additional nodes of the RQT; and
generating two chroma coded block flags (CBFs) at the root node of the RQT, each of the chroma CBFs indicating whether any of the TUs of the CU are associated with a significant chroma coefficient block that is based on samples of a respective chroma component; and

outputting the bitstream.

2. The method of claim 1 , wherein the root node is associated with a Y CBF that indicates whether any of the TUs of the CU are associated with a significant luma coefficient block.

3. The method of claim 1 , wherein:
the root node is associated with a flag,
if the flag has a first value, at least one of the TUs of the CU is associated with a significant coefficient block, and
if the flag has a second value that is different than the first value, none of the TUs of the CU is associated with a significant coefficient block, and no node in the RQT is associated with a Y CBF, a U CBF, or a V CBF.

4. The method of claim 1 , wherein for each respective node in the RQT:
if a Y CBF of the respective node, a U CBF of the respective node, and a V CBF of the respective node all have a first value, the respective node is not associated with a respective split flag indicating whether the respective node has a plurality of child nodes,
if at least one of the Y CBF of the respective node, the U CBF of the respective node, and the V CBF of the respective node has a second value that is different than the first value, the respective node is associated with the respective split flag,
wherein the Y CBF indicates whether any TU that corresponds to the respective node or a descendant node of the respective node is associated with a significant Y coefficient block,
wherein the U CBF indicates whether any TU that corresponds to the respective node or a descendant node of the respective node is associated with a significant U coefficient block, and
wherein the V CBF indicates whether any TU that corresponds to the respective node or a descendant node of the respective node is associated with a significant V coefficient block.

5. The method of claim 1 , further comprising:
selecting, based at least in part on a CBF of a node of the RQT, a coding context; and
performing, based on the selected coding context, context-adaptive binary arithmetic coding (CABAC) encoding on a split flag of the node, the split flag indicating whether the node has a plurality of child nodes.

6. The method of claim 5 , wherein selecting the coding context comprises selecting, based on a Y CBF of the node, a U CBF of the node, and a V CBF of the node, the coding context.

7. The method of claim 1 , further comprising performing, based at least in part on a same coding context, CABAC encoding on a Y CBF, a U CBF, and a V CBF of a node in the RQT.

8. The method of claim 1 , wherein a non-leaf node of the RQT is associated with a split flag, a Y CBF, a U CBF, and a V CBF, the split flag associated with the non-leaf node indicating that the non-leaf node has a plurality of descendant nodes, the Y CBF indicating whether any of the descendant nodes is associated with a significant luma coefficient block, the U CBF indicating whether any of the descendant nodes is associated with a significant U coefficient block, the V CBF indicating whether any of the descendant nodes is associated with a significant V coefficient block.

9. The method of claim 1 , further comprising:
selecting, based on depths of nodes of the RQT, coding contexts for Y, U, and V CBFs specified by the nodes of the RQT; and
performing, based on the coding contexts selected for the Y, U, and V CBFs, entropy encoding operations on the Y, U, and V CBFs.

10. The method of claim 9 , wherein selecting the coding contexts comprises selecting a coding context for a CBF, wherein an index value of the coding context is equal to a depth of a node in the RQT that specifies the CBF.

11. The method of claim 1 , wherein, for each respective node in the RQT:
the respective node does not include a U CBF unless the respective node is the root node or a U CBF of a parent node of the respective node indicates that a descendant node of the parent node is associated with a significant U chroma block; and
the respective node does not include a V CBF unless the respective node is the root node or a V CBF of the parent node of the respective node indicates that a descendant node of the parent node is associated with a significant V chroma block.

12. A method for decoding video data, the method comprising:
receiving a bitstream that includes an encoded representation of the video data, the video data representing a series of pictures;
for each respective node of a residual quad tree (RQT) of a coding unit (CU) of a picture of the series of pictures, responsive to determining a block corresponding to the respective node is larger than a maximum-allowable transform unit (TU) size, automatically splitting, without parsing from the bitstream a split flag for the respective node, the block corresponding to the respective node into four sub-blocks corresponding to additional nodes of the RQT, the RQT including a hierarchy of nodes, a root node of the RQT corresponding to the CU as a whole, and respective leaf nodes of the RQT corresponding to respective TUs of the CU, each of the TUs of the CU being associated with a different residual pixel block;
parsing, from the bitstream, two chroma coded block flags (CBFs) at the root node of the RQT, wherein the CU is larger than the maximum-allowable TU size;
for each of the chroma CBFs, determining, based on the respective chroma CBF, whether any TU of the CU is associated with a significant chroma coefficient block that is based on samples of a respective chroma component;
based on a particular TU of the CU being associated with a significant chroma coefficient block, performing an inverse transform on coefficient blocks to reconstruct the residual pixel block associated with the particular TU of the CU, the significant chroma coefficient block being one of the coefficient blocks; and
reconstructing a video block of the CU based on one or more predictive pixel blocks of prediction units (PUs) of the CU and the residual pixel blocks associated with the TUs of the CU.

13. The method

Assignees

• Qualcomm Inc

Inventors

• Guo Liwei
• Wang Xianglin
• Karczewicz Marta

Classifications

• H04N19/176

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

• H04N19/46

  Embedding additional information in the video signal during the compression process (H04N19/517, H04N19/68, H04N19/70 take precedence) · CPC title

• H04N19/70

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

• H04N19/00969 Primary

  Electricity · mapped topic

• H04N19/96 Primary

  Tree coding, e.g. quad-tree coding · CPC title