SEPARABLE DIRECTIONAL TRANSFORMS

• US 20140112387A1
• Filed: 12/27/2013
• Published: 04/24/2014
• Est. Priority Date: 06/15/2007
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Ye, Yan, Karczewicz, Marta
• Granted Patent: US 9,578,331 B2
• Time in Patent Office: Days
• US Class Current: 375/240.02
• CPC Class Codes: H04N 19/103 Selection of coding mode or of prediction mode
• CPC Class Codes: H04N 19/11 among a plurality of spatial predictive coding modes
• CPC Class Codes: H04N 19/12 Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264
• CPC Class Codes: H04N 19/122 Selection of transform size, e.g. 8x8 or 2x4x8 DCT; Selection of sub-band transforms of varying structure or type
• CPC Class Codes: H04N 19/129 Scanning of coding units, e.g. zig-zag scan of transform coefficients or flexible macroblock ordering [FMO]
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• 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 19/157 Assigned coding mode, i.e. the coding mode being predefined or preselected to be further used for selection of another element or parameter
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/19 using optimisation based on Lagrange multipliers
• CPC Class Codes: H04N 19/196 being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters processing of motion vectors H04N19/513
• CPC Class Codes: H04N 19/197 including determination of the initial value of an encoding parameter H04N19/56 takes precedence
• CPC Class Codes: H04N 19/42 characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation H04N19/635 takes precedence
• 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 19/48 using compressed domain processing techniques other than decoding, e.g. modification of transform coefficients, variable length coding [VLC] data or run-length data motion estimation in a transform domain H04N19/547; processing of decoded motion vectors H04N19/513
• CPC Class Codes: H04N 19/593 involving spatial prediction techniques
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/625 using discrete cosine transform [DCT]
• CPC Class Codes: H04N 19/70 : characterised by syntax aspects related to video coding, e.g. related to compression standards

Abstract

This disclosure describes techniques for transforming residual blocks of video data. In particular, a plurality of different transforms selectively applied to the residual blocks based on the prediction mode of the video blocks. At least a portion of the plurality of transforms are separable directional transform specifically trained for a corresponding prediction mode to provide better energy compaction for the residual blocks of the given prediction mode. Using separable directional transforms offers the benefits of lower computation complexity and storage requirement than use of non-separable directional transforms. Additionally, a scan order used to scan the coefficients of the residual block may be adjusted when applying separable directional transforms. In particular, the scan order may be adjusted based on statistics associated with one or more previously coded blocks to better ensure that non-zero coefficients are grouped near the front of the one-dimensional coefficient vector to improve the effectiveness of entropy coding.

Claims

1. A method of decoding video data, the method comprising:

decoding, from an encoded video bitstream, data associated with a predicted video block having a partition size, wherein the data comprises a prediction mode for predicting pixel values of the predicted video block and a plurality of transform coefficients indicative of a residual associated with the predicted video block, wherein the prediction mode comprises one of a plurality of prediction modes for predicting pixel values in a specified direction;

selecting, based on the prediction mode, one or more separable transforms from a plurality of separable transforms for the partition size,

wherein for a first one of the prediction modes having a first prediction direction and a second one of the prediction modes having a second, different, prediction direction, different transforms are selected based on the prediction mode, and wherein, for the first one of the prediction modes, selecting the one or more transforms comprises selecting a combination of a separable DCT transform and at least one other separable transform;

applying the selected transforms to the plurality of transform coefficients to generate a block of residual values;

generating predicted pixel values of the predicted video block based on the prediction mode; and

generating the predicted video block based on the predicted pixel values and the generated block of residual values.

2. The method of claim 1, wherein the first prediction direction is horizontal and the second prediction direction is vertical.

3. The method of claim 1, wherein the separable DCT transform comprises a separable DCT-like integer transform.

4. The method of claim 1, wherein the separable transforms each comprise a column transform matrix of size N×

N and a row transform matrix of size N×

N, where N×

N is a dimension of the partition size of the predicted video block.

5. A method of encoding video data, the method comprising:

generating predicted pixel values of a video block having a partition size based on a prediction mode, wherein the prediction mode comprises one of a plurality of prediction modes for predicting pixel values in a specified direction;

generating a block of residual values based on the video block and the predicted pixel values;

selecting, based on the prediction mode, one or more separable transforms from a plurality of separable transforms for the partition size,

wherein for a first one of the prediction modes having a first prediction direction and a second one of the prediction modes having a second, different, prediction direction, different transforms are selected based on the prediction mode, and wherein, for the first one of the prediction modes, selecting the one or more transforms comprises selecting a combination of a separable DCT transform and at least one other separable transform;

applying the selected transforms to the plurality of transform coefficients to generate a plurality of transform coefficients; and

entropy encoding data indicative of the prediction mode and the transform coefficients.

6. The method of claim 5, wherein the first prediction direction is horizontal and the second prediction direction is vertical.

7. The method of claim 5, wherein the separable DCT transform comprises a separable DCT-like integer transform.

8. The method of claim 5, wherein the separable transforms each comprise a column transform matrix of size N×

N and a row transform matrix of size N×

N, where N×

N is a dimension of the partition size of the predicted video block.

9. A device for coding video data, the device comprising:

a memory configured to store a plurality of separable transforms for use in transforming between residual pixel values of a video block and residual transform coefficients of the video block, each of the plurality of separable transforms being associated with a partition size; and

a processor configured to;

generate predicted pixel values of a video block having a partition size based on a prediction mode, wherein the prediction mode comprises one of a plurality of prediction modes for predicting pixel values in a specified direction;

select, based on the prediction mode, one or more separable transforms from the plurality of separable transforms for the partition size, wherein for a first one of the prediction modes having a first prediction direction and a second one of the prediction modes having a second, different, prediction direction, different transforms are selected based on the prediction mode, and wherein, for the first one of the prediction modes, selecting the one or more transforms comprises selecting a combination of a separable DCT transform and at least one other separable transform; and

apply the selected separable transforms to transform between residual pixel values associated with the predicted pixel values and residual transform coefficients.

10. The device of claim 9, wherein the first prediction direction is horizontal and the second prediction direction is vertical.

11. The device of claim 9, wherein the separable DCT transform comprises a separable DCT-like integer transform.

12. The device of claim 9, wherein the separable transforms each comprise a column transform matrix of size N×

N and a row transform matrix of size N×

N, where N×

N is a dimension of the partition size of the predicted video block.

13. The device of claim 9, wherein the processor comprises a video encoder, wherein the transforms are transforms for use in transforming residual pixel values of the video block to residual transform coefficients, and wherein the processor is further configured to:

generate residual values of the video block based on the video block and the predicted pixel values,

apply the selected transforms to transform the residual values to the residual transform coefficients; and

encode data indicative of the residual transform coefficients and the prediction mode.

14. The device of claim 9, wherein the processor comprises a video decoder, wherein the transforms are inverse transforms for use in transforming residual transform coefficients to residual pixel values of the video block, and wherein the processor is further configured to:

decode data indicative of the prediction mode and residual transform coefficients of the video block;

apply the selected transforms to transform the residual transform coefficients to the residual values of the video block; and

generate a video block based on the residual values of the video block and the predicted video block.

15. The device of claim 13, wherein the device comprises a wireless communication device having a display, the display being configured to display the coded video data.

16. The device of claim 9, wherein the device comprises an integrated circuit device.

17. A non-transitory computer-readable medium upon which is stored instructions that upon execution in a device cause the device to code video blocks, wherein the instructions cause the device to:

generate predicted pixel values of a video block having a partition size based on a prediction mode, wherein the prediction mode comprises one of a plurality of prediction modes for predicting pixel values in a specified direction;

select, based on the prediction mode, one or more separable transforms from a plurality of separable transforms for use in transforming between residual pixel values of a video block and residual transform coefficients of the video block, each of the plurality of separable transforms being associated with a partition size, wherein for a first one of the prediction modes having a first prediction direction and a second one of the prediction modes having a second, different, prediction direction, different transforms are selected based on the prediction mode, and wherein, for the first one of the prediction modes, selecting the one or more transforms comprises selecting a combination of a separable DCT transform and at least one other separable transform; and

apply the selected separable transforms to transform between residual pixel values associated with the predicted pixel values and residual transform coefficients;

18. A device for coding video data, the device comprising:

means for storing a plurality of separable transforms for use in transforming between residual pixel values of a video block and residual transform coefficients of the video block, each of the plurality of separable transforms being associated with a partition size; and

means for processing video data configured to;

generate predicted pixel values of a video block having a partition size based on a prediction mode, wherein the prediction mode comprises one of a plurality of prediction modes for predicting pixel values in a specified direction;

select, based on the prediction mode, one or more separable transforms from the plurality of separable transforms for the partition size, wherein for a first one of the prediction modes having a first prediction direction and a second one of the prediction modes having a second, different, prediction direction, different transforms are selected based on the prediction mode, and wherein, for the first one of the prediction modes, selecting the one or more transforms comprises selecting a combination of a separable DCT transform and at least one other separable transform; and

apply the selected separable transforms to transform between residual pixel values associated with the predicted pixel values and residual transform coefficients;

19. The device of claim 18, wherein the video processing means comprises means for encoding video, wherein the transforms are transforms for use in transforming residual pixel values of the video block to residual transform coefficients, and wherein the video processing means is further configured to:

generate residual values of the video block based on the video block and the predicted pixel values,

apply the selected transforms to transform the residual values to the residual transform coefficients; and

encode data indicative of the residual transform coefficients and the prediction mode.

20. The device of claim 18, wherein the video processing means comprises means for decoding video data, wherein the transforms are inverse transforms for use in transforming residual transform coefficients to residual pixel values of the video block, and wherein the video processing means is further configured to:

decode data indicative of the prediction mode and residual transform coefficients of the video block;

apply the selected transforms to transform the residual transform coefficients to the residual values of the video block; and

generate a video block based on the residual values of the video block and the predicted video block.