Method, device, computer program, and information storage means for encoding or decoding a video sequence

• US 20140192869A1
• Filed: 01/02/2014
• Published: 07/10/2014
• Est. Priority Date: 01/04/2013
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: LAROCHE, GUILLAUME, GISQUET, CHRISTOPHE, ONNO, PATRICE, FRANOIS, EDOUARD
• Granted Patent: US 10,298,937 B2
• Time in Patent Office: Days
• US Class Current: 375/240.12
• CPC Class Codes: H04N 19/117 Filters, e.g. for pre-processing or post-processing sub-band filter banks H04N19/635
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/147 according to rate distortion criteria rate-distortion as a criterion for motion estimation H04N19/567
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/19 using optimisation based on Lagrange multipliers
• CPC Class Codes: H04N 19/82 involving filtering within a prediction loop
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness

Abstract

The invention relates to video coding. A method of encoding or decoding such a video sequence according to the invention comprises: obtaining a reconstructed frame area made of an array of sample values; applying a sample adaptive offset, SAO, filtering to the reconstructed frame area based on SAO parameters; wherein at least one of the SAO parameters is determined independently of the sample values of the reconstructed frame area. Preferably, the sample-independent SAO parameters define an Edge Offset filtering.

Claims

1. A method of encoding or decoding a video sequence, the method comprising decoding an encoded frame into a decoded frame, wherein decoding the encoded frame comprises:

obtaining a reconstructed frame area made of an array of sample values;

applying a sample adaptive offset, SAO, filtering to the reconstructed frame area based on SAO parameters;

wherein at least one of the SAO parameters is determined independently of the sample values of the reconstructed frame area.

2. The method of claim 1, wherein the SAO parameters include a SAO filtering type, a SAO-type-depending parameter and offsets, wherein the at least one SAO parameter includes the offsets.

3. The method of claim 2, wherein the offsets of the at least one SAO parameter includes four prefixed offsets equal to |1, 0, 0 −

1|.

4. The method of claim 2, wherein the offsets of the at least one SAO parameter includes four offsets O1, O2, O3, O4 such that O1>

O2≧

0≧

O3>

O4 and |O1=|O4| and |O2|=|O3|, where |x| is the absolute value of x; and

the offsets depend on a quantization parameter used to decode a frame area of the encoded frame.

5. The method of claim 2, wherein the at least one SAO parameter further includes the SAO filtering type.

6. The method of claim 5, wherein the SAO filtering type determined independently of the sample values is set to Edge Offset filtering.

7. The method of claim 2, wherein the at least one SAO parameter includes all the SAO parameters, including the SAO-type-depending parameter.

8. The method of claim 7, wherein the SAO filtering type is a SAO Edge Offset filtering and the SAO-type-depending parameter is a direction of Edge Offset filtering.

9. The method of claim 8, wherein the Edge Offset direction is prefixed for a plurality of frames of the video sequence.

10. The method of claim 9, wherein the prefixed Edge Offset direction is a horizontal direction.

11. The method of claim 8, wherein the Edge Offset direction is selected for each new frame within the video sequence, based on a picture order count associated with each new frame.

12. The method of claim 9, wherein vertical and horizontal Edge Offset directions are favored for selection compared to diagonal Edge Offset directions.

13. The method of claim 12, wherein the diagonal Edge Offset directions are disabled for selection.

14. The method of claim 8, wherein the Edge Offset direction is perpendicular to an Edge Offset direction determined for a co-located frame area in another frame of the video sequence.

15. The method of claim 8, wherein the Edge Offset direction is determined based on a direction for spatial prediction associated with the reconstructed frame area.

16. The method of claim 15, wherein the Edge Offset direction is the closest direction to a perpendicular of the spatial prediction direction, from amongst predefined directions.

17. The method of claim 1, wherein frames of the video sequence are encoded using temporal prediction according to a temporal prediction frame hierarchy between frames;

and the SAO filtering is enabled for frame areas belonging to a frame having a lower depth according to the temporal prediction frame hierarchy, the SAO filtering is disabled for frame areas belonging to a frame having a higher depth according to the temporal prediction frame hierarchy, and enabling SAO filtering for frame areas belonging to a frame having a middle depth according to the temporal prediction frame hierarchy depends on quantization parameters associated with the depths or on Lagrange parameter λ

.

18. The method of claim 1, wherein SAO parameters are determined for another frame of the video sequence;

and the SAO parameters to be used for SAO-filtering the reconstructed frame area are;

by-default SAO parameters if the SAO parameters determined for a co-located frame area in the other frame define no SAO filtering or a Band Offset filtering,

the same SAO parameters, except a perpendicular Edge Offset direction, as those determined for a co-located frame area in the other frame if those determined parameters define an Edge Offset filtering.

19. The method of claim 1, further comprising cascading several SAO filterings on the reconstructed frame area based on respective sets of SAO parameters, wherein at least one SAO parameter of each respective set of SAO parameters is determined independently of the sample values of the reconstructed frame area.

20. The method of claim 19, wherein three Edge Offset SAO filterings are cascaded corresponding to three Edge Offset directions that are different from an Edge Offset direction determined for a co-located frame area in another frame of the video sequence.

21. The method of claim 19, wherein the bitstream comprises a plurality of flags to specify whether associated Edge Offset directions are enabled or not.

22. The method of claim 19, wherein the direction of the SAO filtering first occurring in the cascade is determined based on an Edge Offset direction determined for a co-located frame area in another frame of the video sequence.

23. The method of claim 19, wherein the several cascaded SAO filterings uses the same set of offsets.

33. A non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device, causes the device to perform the steps of any of claim 1.

24. A device for encoding or decoding a video sequence, comprising an internal decoder configured to decode an encoded frame into a decoded frame, wherein the internal decoder comprises:

a frame area module configured to obtain a reconstructed frame area made of an array of sample values;

a sample adaptive offset, SAO, filter configured to apply a SAO filtering to the reconstructed frame area based on SAO parameters;

a SAO parameter determining module configure to determine at least one of the SAO parameters independently of the sample values of the reconstructed frame area.

25. The device of claim 24, wherein the SAO parameters include a SAO filtering type, a SAO-type-depending parameter and offsets, wherein the at least one SAO parameter includes the offsets.

26. The device of claim 25, wherein the offsets of the at least one SAO parameter includes four prefixed offsets equal to |1, 0, 0 −

1|.

27. The device of claim 25, wherein the at least one SAO parameter further includes the SAO filtering type.

28. The device of claim 25, wherein the at least one SAO parameter includes all the SAO parameters, including the SAO-type-depending parameter.

29. The device of claim 28, wherein the SAO filtering type is a SAO Edge Offset filtering and the SAO-type-depending parameter is a direction of Edge Offset filtering.

30. The device of claim 24, wherein frames of the video sequence are encoded using temporal prediction according to a temporal prediction frame hierarchy between frames;

and the device is configured to enable SAO filtering for frame areas belonging to a frame having a lower depth according to the temporal prediction frame hierarchy, to disable SAO filtering for frame areas belonging to a frame having a higher depth according to the temporal prediction frame hierarchy, and to enable SAO filtering for frame areas belonging to a frame having a middle depth according to the temporal prediction frame hierarchy depending on quantization parameters associated with the depths or on Lagrange parameter λ

.

31. The device of claim 24, wherein SAO parameters are determined for another frame of the video sequence;

and the SAO parameters to be used for SAO-filtering the reconstructed frame area are;

by-default SAO parameters if the SAO parameters determined for a co-located frame area in the other frame define no SAO filtering or a Band Offset filtering,

the same SAO parameters, except a perpendicular Edge Offset direction, as those determined for a co-located frame area in the other frame if those determined parameters define an Edge Offset filtering.

32. The device of claim 24, comprising several SAO filters in cascade to cascade several SAO filterings on the reconstructed frame area based on respective sets of SAO parameters, wherein at least one SAO parameter of each respective set of SAO parameters is determined independently of the sample values of the reconstructed frame area.