Method and system for decoder-side intra mode derivation for block-based video coding

Patent metadata

Field	Value
Publication number	US-2019166370-A1
Application number	US-201716096236-A
Country	US
Kind code	A1
Filing date	May 5, 2017
Priority date	May 6, 2016
Publication date	May 30, 2019
Grant date	—

Abstract

Systems and methods related to video encoding and decoding using decoder-side intra mode derivation (DIMD) are described. In an exemplary method of coding samples in a block in a video, an intra coding mode is selected based on a plurality of reconstructed samples in a template region adjacent to the block, and the samples in the block are predicted with intra prediction using the selected intra coding mode. The intra coding mode may be selected by testing a plurality of candidate intra coding modes for cost (e.g. distortion) of predicting the template region from a set of reconstructed reference samples. The mode with the lowest cost is used for prediction. In exemplary embodiments, explicit signaling of the intra mode is not required.

First claim

1 . A method of coding a video in a bitstream, wherein the video comprises a plurality of frames, each frame comprising blocks of samples, the method comprising, for at least a current block:
for each of a plurality of candidate intra coding modes, determining a cost of using the respective candidate mode to predict samples in a template region adjacent to the current block, wherein determining the cost comprises:
in an initial stage, determining the cost for each of an initial set of candidate modes; and
in at least one subsequent stage, selecting a subsequent set of candidate modes based on the candidate mode in the previous stage having the lowest cost;
selecting a derived intra coding mode from the plurality of candidate intra coding modes based on the cost; and predicting the samples in the current block with intra prediction using the derived intra coding mode.

2 . The method of claim 1 , wherein the cost is a measure of distortion between the template region and a prediction of the template region using the respective candidate intra coding mode.

3 . The method of claim 1 wherein determining the cost of a candidate intra coding mode comprises:
using the respective candidate intra coding mode to generate a prediction of the template region from a set of reconstructed reference samples; and
measuring distortion between the template region and the prediction of the template region.

4 . The method of claim 1 , wherein the template region comprises reconstructed samples adjacent to the current block.

5 . The method of claim 1 wherein the bitstream includes a flag indicating that decoder-side intra mode derivation is used for the current block.

6 . The method of claim 1 , wherein the initial set of candidate modes includes a planar mode and a DC mode, and wherein the subsequent set of candidate modes is selected only in response to a determination that neither the planar nor the DC mode is the candidate mode having the lowest cost.

7 . The method of claim 1 , wherein the subsequent set of candidate modes is centered on the candidate mode in the previous stage having the lowest cost.

8 . The method of claim 1 , wherein determining the cost is performed for no more than a predetermined maximum number of stages.

9 . (canceled)

10 . The method of claim 1 wherein at least some blocks in the video are predicted using a predetermined set of explicitly-signaled intra modes, wherein the candidate intra modes have a finer granularity than the predetermined set of explicitly-signaled intra modes.

11 . (canceled)

12 . The method of claim 1 , wherein
in the initial stage, the modes in the initial set are separated by an initial interval; and in the at least one subsequent stage, the modes in the subsequent set are separated by a subsequent interval smaller than the interval used in the previous stage.

13 . The method of claim 1 wherein the selected derived mode is included in a list of most probable modes.

14 . The method of claim 13 , wherein an index is coded in the bitstream identifying the selected derived mode from the list of most probable modes.

15 . The method of claim 1 wherein prediction residuals for the samples in the current block are coded in the bitstream using a transform coefficient scanning order, and wherein the transform coefficient scanning order is independent of the selected derived mode.

16 . The method of claim 15 , wherein the transform coefficient scanning order is a predetermined scanning order.

17 . The method of claim 15 , wherein the transform coefficient scanning order is based on intra modes of spatial neighbors of the current block.

18 . The method of claim 1 , performed by a video encoder.

19 . The method of claim 1 , performed by a video decoder.

20 . A video encoder for encoding a video in a bitstream, wherein the video comprises a plurality of frames, each frame comprising blocks of samples, the method comprising, for at least a current block, the encoder being operative to perform functions comprising:
for each of a plurality of candidate intra coding modes, determining a cost of using the respective candidate mode to predict a template region adjacent to the current block, wherein determining the cost comprises:
in an initial stage, determining the cost for each of an initial set of candidate modes; and
in at least one subsequent stage, selecting a subsequent set of candidate modes based on the candidate mode in the previous stage having the lowest cost;
selecting a derived intra coding mode from the plurality of candidate intra coding modes based on the cost; and predicting the samples in the current block with intra prediction using the derived intra coding mode.

21 . A video decoder for decoding a video from a bitstream, wherein the video comprises a plurality of frames, each frame comprising blocks of samples, the method comprising, for at least a current block, the decoder being operative to perform functions comprising:
for each of a plurality of candidate intra coding modes, determining a cost of using the respective candidate mode to predict a template region adjacent to the current block, wherein determining the cost comprises:
in an initial stage, determining the cost for each of an initial set of candidate modes; and
in at least one subsequent stage, selecting a subsequent set of candidate modes based on the candidate mode in the previous stage having the lowest cost;
selecting a derived intra coding mode from the plurality of candidate intra coding modes based on the cost; and predicting the samples in the current block with intra prediction using the derived intra coding mode.

Assignees

• Vid Scale Inc

Inventors

• Xiu Xiaoyu
• He Yuwen
• Ye Yan

Classifications

• H04N19/176

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

• H04N19/154 Primary

  Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion (use of rate-distortion criteria H04N19/147) · CPC title

• H04N19/147

  according to rate distortion criteria (rate-distortion as a criterion for motion estimation H04N19/567) · CPC title

• H04N19/11

  among a plurality of spatial predictive coding modes · CPC title