CONTENT ADAPTIVE MOTION COMPENSATION FILTERING FOR HIGH EFFICIENCY VIDEO CODING

• US 20120155533A1
• Filed: 12/21/2010
• Published: 06/21/2012
• Est. Priority Date: 12/21/2010
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Puri, Atul, Socek, Daniel, Choi, Chang-Kee
• Granted Patent: US 8,761,245 B2
• Time in Patent Office: Days
• US Class Current: 375/240.02
• 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 19/134 characterised by the element, parameter or criterion affecting or controlling the adaptive coding
• CPC Class Codes: H04N 19/136 Incoming video signal characteristics or properties
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/46 Embedding additional information in the video signal during the compression process H04N19/517, H04N19/68, H04N19/70 take precedence
• CPC Class Codes: H04N 19/463 by compressing encoding parameters before transmission
• CPC Class Codes: H04N 19/52 by predictive encoding
• CPC Class Codes: H04N 19/523 with sub-pixel accuracy
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/615 using motion compensated temporal filtering [MCTF]
• CPC Class Codes: H04N 19/70 characterised by syntax aspects related to video coding, e.g. related to compression standards
• CPC Class Codes: H04N 19/80 Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation H04N19/635, H04N19/86 take precedence
• 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

A system and method for adaptive motion filtering to improve subpel motion prediction efficiency of interframe motion compensated video coding is described. The technique uses a codebook approach that is efficient in search complexity to look-up best motion filter set from a pre-calculated codebook of motion filter coefficient set. In some embodiments, the search complexity is further reduced by partitioning the complete codebook into a small base codebook and a larger virtual codebook, such that the main calculations for search only need to be performed on the base codebook.

Claims

1. A video-encoder-device-implemented method for encoding an adaptive motion-compensation filter set for a plurality of subpel positions for predicting blocks in an encoded video frame, the method comprising:

obtaining, by the video encoder device, a codebook comprising a multiplicity of motion-compensation filters grouped into a plurality of subpel-position groups that respectively correspond to the plurality of subpel positions, each of the plurality of subpel-position groups comprising a plurality of motion-compensation filters suitable for interpolating blocks of a picture at a corresponding one of the plurality of subpel positions;

obtaining, by the video encoder device, an unencoded frame of video for encoding by the video encoder device;

encoding, by the video encoder device, at least a portion of the frame of video to a bitstream, the portion of the frame of video comprising a plurality of blocks of picture content; and

during encoding of at least the portion of the frame of video, the video encoder device;

selecting from the codebook a subset of the plurality of motion-compensation filters as being well-adapted for predicting the plurality of blocks of picture content, the selected subset comprising one from each of the plurality of subpel-position groups; and

including in the bitstream a subpel-filter code identifying the selected subset of the plurality of motion-compensation filters within the codebook.

2. The method of claim 1, wherein selecting the subset of the plurality of motion-compensation filters comprises selecting one of a plurality of pre-determined subsets of the plurality of motion-compensation filters.

3. The method of claim 2, wherein the code included in the bitstream comprises an index identifying the selected subset among the plurality of pre-determined subsets.

4. The method of claim 2, wherein selecting the one of the plurality of pre-determined subsets of the plurality of motion-compensation filters comprises:

for each of the plurality of blocks of picture content, respectively determining a multiplicity of individual coding gains for the multiplicity of motion-compensation filters;

using the determined multiplicities of individual coding gains, determining an aggregate coding gain for each of the plurality of pre-determined subsets of the plurality of motion-compensation filters as applied to the plurality of blocks of picture content; and

selecting one of the plurality of pre-determined subsets as having a favorable aggregate coding gain for the plurality of blocks of picture content.

5. The method of claim 4, further comprising:

determining a default aggregate coding gain for a default filter set applied to the plurality of blocks of picture content, the default picture set comprising a plurality of default subpel motion-compensation filters corresponding respectively to the plurality of subpel positions; and

determining that the favorable aggregate coding gain is more favorable than the default aggregate coding gain.

6. The method of claim 1, further comprising:

obtaining a plurality of integer-position motion-compensation filters; and

during encoding of at least the portion of the frame of video, the video encoder device selecting one of the plurality of integer-position motion-compensation filters as being well-adapted for predicting the plurality of blocks of picture content.

7. The method of claim 6, further comprising:

determining that the selected one of the plurality of integer-position motion-compensation filters provides better coding gain than the selected subset of the plurality of motion-compensation filters; and

including in the bitstream generated by the video encoder device;

an integer-filter code identifying the selected one of the plurality of integer-position motion-compensation filters; and

an integer-filter flag indicating that the integer-filter code is included in the bitstream for at least the portion of the frame of video.

8. The method of claim 6, wherein the codebook further comprises the plurality of integer-position motion-compensation filters.

9. The method of claim 6, wherein obtaining the plurality of integer-position motion-compensation filters comprises obtaining an integer-position codebook.

10. The method of claim 1, wherein obtaining the codebook comprises:

determining a plurality of default motion-compensation filters corresponding respectively to the plurality of subpel positions;

generating a plurality of subpel-position groups corresponding respectively to the plurality of subpel positions by performing at least steps (i), (ii), and (iii) for each of the plurality of subpel positions;

(i) iteratively refining the corresponding one of the plurality of default motion-compensation filters to generate a multiplicity of refined motion-compensation filters corresponding to the current subpel position;

(ii) determining a multiplicity of coding gains corresponding respectively to the multiplicity of refined motion-compensation filters;

(iii) according to the determined multiplicity of coding gains, selecting from the generated multiplicity of refined motion-compensation filters a subpel-position group of good-performing motion-compensation filters corresponding to the current subpel position.

11. The method of claim 10, further comprising selecting a plurality of subsets of good-performing motion-compensation filters, each subset comprising one good-performing motion-compensation filter selected from each of the plurality of subpel-position groups.

12. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, perform the method of claim 1.

13. A video-encoding apparatus comprising a processor and a storage medium storing instructions that, when executed by the processor, perform the method of claim 1.

14. A video-decoder-device-implemented method for decoding an adaptive motion-compensation filter set for a plurality of subpel positions for predicting blocks of an encoded video frame, the method comprising:

obtaining, by the video decoder device, a codebook comprising a multiplicity of motion-compensation filters grouped into a plurality of subpel-position groups that respectively correspond to the plurality of subpel positions, each of the plurality of subpel-position groups comprising a plurality of motion-compensation filters suitable for interpolating blocks of a picture at a corresponding one of the plurality of subpel positions;

obtaining an encoded bitstream comprising the encoded video frame and a subpel-filter code identifying the adaptive motion-compensation filter set within the codebook, the adaptive motion-compensation filter set comprising a plurality of motion-compensation filters respectively corresponding to the plurality of subpel positions;

during decoding of the encoded video frame, the video decoder device selecting from the codebook the adaptive motion-compensation filter set identified by the subpel-filter code;

using the adaptive motion-compensation filter set, predicting a plurality of blocks of picture content, the plurality of blocks corresponding to at least a portion of the encoded picture frame;

generating a decoded picture according to at least the predicted plurality of blocks of picture content; and

rendering the generated decoded picture to a display associated with the video decoder device.

15. The method of claim 14, wherein the encoded bitstream further includes:

a second subpel-filter code, identifying a second adaptive motion-compensation filter set within the codebook; and

at least one portion-identification code enabling the video decoder to identify the portion of the encoded picture frame and a second portion of the encoded picture frame.

16. The method of claim 15, further comprising:

during decoding of the encoded video frame, the video decoder device selecting from the codebook the second adaptive motion-compensation filter set identified by the second subpel-filter code;

using the second adaptive motion-compensation filter set, predicting a second plurality of blocks of picture content, the second plurality of blocks corresponding to at least a second portion of the encoded picture frame; and

wherein the decoded picture is generated further according to the predicted second plurality of blocks of picture content.

17. The method of claim 14, further comprising obtaining a plurality of integer-position motion-compensation filters.

18. The method of claim 17, wherein the encoded bitstream further comprises:

at least one portion-identification code enabling the video decoder to identify the portion of the encoded picture frame and a second portion of the encoded picture frame; and

an integer-filter code identifying one of the plurality of integer-position motion-compensation filters; and

an integer-filter flag indicating that the integer-filter code is included in the bitstream for at least the second portion of the frame of video.

19. The method of claim 18, further comprising, during decoding of the encoded video frame:

reading the integer-filter flag and responsively selecting from the plurality of integer-position motion-compensation filters the integer-position motion-compensation filter identified by the integer-filter code;

using the selected integer-position motion-compensation filter, predicting a second plurality of blocks of picture content, the second plurality of blocks corresponding to at least the second portion of the encoded picture frame; and

wherein the decoded picture is generated further according to the predicted second plurality of blocks of picture content.

20. The method of claim 17, wherein the codebook further comprises the plurality of integer-position motion-compensation filters.

21. The method of claim 17, wherein obtaining the plurality of integer-position motion-compensation filters comprises obtaining an integer-position codebook.

22. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, perform the method of claim 14.

23. A video-encoding apparatus comprising a processor and a storage medium storing instructions that, when executed by the processor, perform the method of claim 14.