Coding of intra modes

Patent metadata

Field	Value
Publication number	US-2017366807-A1
Application number	US-201515533778-A
Country	US
Kind code	A1
Filing date	Dec 3, 2015
Priority date	Dec 8, 2014
Publication date	Dec 21, 2017
Grant date	—

Abstract

A method of encoding a video image includes, for each one of blocks of the video image, calculating virtual gradient values in the block depending on neighboring gradient values computed in a causal neighborhood of the block and acquiring one prediction direction or non-directional intra prediction mode based on the virtual gradient values; and determining a coding mode by comparing different predictions for the block, acquiring a predicted block by applying the determined “coding mode”, acquiring a residual error between the predicted block and the current block and encoding a difference between the determined coding mode and the prediction direction or non-directional intra prediction mode. The calculating includes, for each prediction direction, propagating the neighboring gradient values along the prediction direction to estimate the virtual gradient values in the block.

First claim

1 . A method of encoding a video image comprising:
for a block of the video image, (a) calculating first gradient values in a causal neighborhood of the block; (b) for each of intra prediction directions, calculating second gradient values in the block by predicting the first gradient values along the each of intra prediction directions; (c) for the each of the intra prediction directions, acquiring an energy value from the second gradient values in the block; (d) acquiring an energy value for at least one non-directional intra prediction mode by using the acquired energy values for the prediction directions; and (e) determining, for the block, an intra prediction mode among directional modes for the intra prediction directions and the at least one non-directional intra prediction mode based on the acquired energy values.

2 . (canceled)

3 . The method according to claim 1 , wherein the first gradient values are obtained by filtering pixel values in the causal neighborhood of the block, the filtering is related to the intra prediction directions, and (2N+1)×(2N+1) pixel values are used for each of the first gradient values, the N being a positive integer.

4 . (canceled)

5 . The method according to claim 1 , wherein the energy value is the summation of absolute values of the second gradient values or a maximum value among absolute values of the second gradient values.

6 . The method according to claim 1 , wherein the energy value is obtained by averaging the acquired energy values for the intra prediction directions.

7 . The method according to claim 1 , wherein the intra prediction mode is determined as an intra prediction mode for which the energy value is the highest among the acquired energy values.

8 . The method according to claim 7 , wherein if the intra prediction mode for which the energy value is the highest among the acquired energy values is for at least one non-directional intra prediction mode and if there are several non-directional intra prediction modes, the intra prediction mode is determined according to an estimation error of predicted pixel values based on the at least one of non-directional intra prediction modes and pixel values in the causal neighborhood of the block.

9 . The method according to claim 1 , further comprising:
(f) encoding the block using a second intra prediction mode based on RDO; and (g) encoding the index of the second intra prediction mode with respect to the determined intra prediction mode.

10 - 14 . (canceled)

15 . A method of decoding an encoded video image comprising:
for a block of the encoded video image, (a) calculating first gradient values in a causal neighborhood of the block; (b) for each of intra prediction directions, calculating second gradient values in the block by extrapolating the first gradient values along the each of intra prediction directions (S 120 ); (c) for the each of the intra prediction directions, acquiring an energy value from the second values in the block; (d) acquiring an energy value for at least one non-directional intra prediction mode by using the acquired energy values for the intra prediction directions; and (e) determining, for the block, an intra prediction mode based on said acquired energy values corresponding to directional modes for the intra prediction directions and the at least one non-directional intra prediction mode.

16 . The method according to claim 15 , wherein the first gradient values are obtained by filtering pixel values in the causal neighborhood of the block, the filtering is related to the intra prediction directions, and (2N+1)×(2N+1) pixel values are used for each of the first gradient values, the N being a positive integer.

17 . The method according to claim 15 , wherein the energy value is the summation of absolute values of the second gradient values or a maximum value among absolute values of the second gradient values.

18 . The method according to claim 15 , wherein the energy value is obtained by averaging the acquired energy values for the intra prediction directions.

19 . The method according to claim 15 , wherein the intra prediction mode is determined as an intra prediction mode for which the energy value is the highest among the acquired energy values.

20 . The method according to claim 19 , wherein if the intra prediction mode for which the energy value is the highest among the acquired energy values is for at least one the non-directional intra prediction mode and if there are several non-directional intra prediction modes, the intra prediction mode is determined according to an estimation error of predicted pixel values based on the at least one of non-directional intra prediction modes and pixel values in the causal neighborhood of the block.

21 . The method according to claim 15 , further comprising
(f2) decoding the block using a second prediction mode decoded based on the determined intra prediction mode.

22 . An apparatus for encoding a video image or decoding a decoding an encoded video image, comprising a processor configured to for each one of blocks of the video image,
(a) calculate first gradient values in a causal neighborhood of the block; (b) for each of intra prediction directions, calculate second gradient values in the block by predicting the first gradient values along the each of intra prediction directions (S 120 ); (c) for the each of the intra prediction directions, acquire an energy value from the second gradient values in the block; (d) acquire an energy value for at least one non-directional intra prediction mode by using the acquired energy values for the prediction directions; and (e) determine, for the block, an intra prediction mode among directional modes for the intra prediction directions and the at least one non-directional intra prediction mode based on the acquired energy values.

23 . The apparatus according to claim 22 , wherein the first gradient values are obtained by filtering pixel values in the causal neighborhood of the block, the filtering is related to the intra prediction directions, and (2N+1)×(2N+1) pixel values are used for each of the first gradient values, the N being a positive integer.

24 . The apparatus according to claim 22 , wherein the energy value is the summation of absolute values of the second gradient values or a maximum value among absolute values of the second gradient values.

25 . The apparatus according to claim 22 , the energy value is obtained by averaging the acquired energy values for the intra prediction directions.

26 . The apparatus according to claim 22 , wherein the intra prediction mode is determined as an intra prediction mode for which the energy value is the highest among the acquired energy values.

27 . The apparatus according to claim 22 , wherein the processor is further configured to:
(f) encode the block using a second intra prediction mode based on RDO; and (g) encode the index of the second intra prediction mode with respect to the determined intra prediction mode.

28 . An apparatus for decoding an encoded video image, comprising a processor configured, for a block of the encoded video image, to:
(a) calculate first gradient values in a causal neighborhood of the block; (b) for each of intra prediction directions, calculate second gradient values in the block by extrapolating the first gradient values along the each of intra prediction directions; (c) for the each of the intra pre

Assignees

• Thomson Licensing

Inventors

• Thoreau Dominique
• Alain Martin
• Le Pendu Mikael
• Turkan Mehrnet

Classifications

• H04N19/44

  Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder · CPC title

• H04N19/593

  involving spatial prediction techniques · CPC title

• H04N19/463

  by compressing encoding parameters before transmission · CPC title

• H04N7/12

  Systems in which the television signal is transmitted via one channel or a plurality of parallel channels, the bandwidth of each channel being less than the bandwidth of the television signal (H04N7/24 takes precedence) · CPC title

• H04N11/02

  with bandwidth reduction (H04N11/04 {, H04N11/24} take precedence) · CPC title