SYSTEM AND METHOD FOR VIDEO ENCODING USING ADAPTIVE LOOP FILTER

• US 20100061645A1
• Filed: 12/05/2008
• Published: 03/11/2010
• Est. Priority Date: 09/11/2008
• Status: Active Grant

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: ON2 Technologies Incorporated (Alphabet Inc.)
• Inventors: Bankoski, James, Wilkins, Paul, Xu, Yaowu
• Granted Patent: US 8,326,075 B2
• Time in Patent Office: Days
• US Class Current: 382/238
• 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 19/139 Analysis of motion vectors, e.g. their magnitude, direction, variance or reliability
• CPC Class Codes: H04N 19/159 Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/50 using predictive coding H04N19/61 takes precedence
• CPC Class Codes: H04N 19/513 Processing of motion vectors
• CPC Class Codes: H04N 19/65 using error resilience
• 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

Disclosed herein is a method for reducing blocking artifacts at the boundary between adjacent blocks reconstructed from a frame of compressed video information. The video information includes a prediction stage parameter with respect to at least one of the blocks. The method includes reconstructing the at least one block based on the prediction stage parameter, computing a residual error attribute from the reconstructed block, computing a filter strength value based on a baseline filter strength and at least one incremental value, wherein the incremental value is selected from a plurality of preset values based at least on one of the prediction stage parameter and residual error attribute associated with the at least one block and filtering the boundary adjacent to the at least one block using the selected filter strength value.

Claims

1. A method for reducing blocking artifacts at the boundary between adjacent blocks reconstructed from a frame of compressed video information that includes a prediction stage parameter with respect to at least one of the blocks, the method comprising:

reconstructing the at least one block based on the prediction stage parameter;

computing a residual error attribute from the reconstructed block;

computing a filter strength value based on a baseline filter strength and at least one incremental value, the incremental value selected from a plurality of preset values based at least on one of the prediction stage parameter and residual error attribute associated with the at least one block; and

filtering the boundary adjacent to the at least one block using the selected filter strength value.

2. The method of claim 1, wherein the prediction stage parameter includes at least one of a reference frame type and a prediction mode.

3. The method of claim 2, wherein the reference frame type is one of intra-frame, last frame, golden frame and alternate reference frame.

4. The method of claim 2, wherein the prediction mode is one of non-split mode and split mode.

5. The method of claim 1, wherein computing the filter strength value further comprises computing the filter strength value based on a second incremental value selected from the plurality of preset values based on the other one of the prediction stage parameter and residual error attribute.

6. The method of claim 5, wherein the residual error attribute is one of a null motion vector and a non-zero motion vector.

7. The method of claim 1 wherein the plurality of preset values are determined at the frame level.

8. The method of claim 7, further comprising:

determining whether the frame being decoded is a key frame; and

wherein the at least one incremental value is set to a default value if the frame being decoded is a key frame.

9. The method of claim 7, further comprising:

determining whether the frame being decoded specifies a loop filter strength value condition; and

if the frame being decoded specifies a loop filter strength value condition, then assigning specified loop filter strength values to the plurality of preset values.

10. The method of claim 7, further comprising:

determining whether the frame being decoded specifies a single loop filter condition; and

if the frame being decoded specifies a single loop filter condition, then assigning a single loop filter strength value to the blocks without regard to the prediction stage parameter and residual error attribute associated with the at least one block.

11. A method for decoding frames of compressed video information, each frame including a plurality of blocks having a prediction stage parameter and a residual error attribute comprising:

categorizing each of the blocks into categories based on at least one of the prediction stage parameter and the residual error attribute;

determining a loop filter strength value to each of the categories; and

filtering the boundary adjacent to at least one of the blocks using the loop filter strength assigned to the category in which that block is categorized.

12. The method of claim 11, wherein determining a loop filter strength value for a given category comprises:

determining a baseline loop filter strength value specified in at least one frame;

determining one or more preset incremental values for the given category based on at least one of the prediction stage parameter and the residual error attribute associated with that category; and

adding the one or more preset incremental values to the baseline loop filter strength value.

13. The method of claim 11, wherein the prediction stage parameter includes at least one of a reference frame type and a prediction mode.

14. The method of claim 13, wherein the reference frame type is one of intra-frame, last frame, golden frame and alternate reference frame.

15. The method of claim 13, wherein the prediction mode is one of non-split mode and split mode.

16. The method of claim 11, wherein the residual error attribute is one of a null motion vector and a non-zero motion vector.

17. The method of claim 11, wherein assigning a loop filter strength value for each one of the categories further comprises:

determining the loop filter strength value for each category from a set of loop filter modifiers specified in at least one of the frames.

18. The method of claim 17, further comprising:

determining whether the frame being decoded is a key frame; and

wherein the loop filter strength value for at least one of the preset categories is set to a default value if the frame being decoded is a key frame.

19. The method of claim 18, further comprising:

determining whether the frame being decoded specifies a loop filter strength value condition for one or more of the categories; and

if the frame being decoded specifies a loop filter strength value condition for one or more of the categories, then assigning that specified loop filter strength values to the one or more categories.

20. The method of claim 11, further comprising:

determining whether the frame being decoded specifies a single loop filter condition; and

if the frame being decoded specifies a single loop filter condition, then assigning a single loop filter strength value to all blocks without regard to category.

21. A method for decoding frames of compressed video information, each frame including a plurality of blocks each having a prediction stage parameter and a residual error attribute comprising:

determining the block attributes for each block;

determining a plurality of values of one or more loop filter attributes, each value associated with one or more block attributes;

selecting one of the plurality of values of one or more loop filter attributes for a particular block based on that block'"'"'s block attributes; and

filtering the boundary adjacent to the particular block using the selected one or more loop filter attribute values.

22. The method of claim 21, wherein the loop filter attributes include at least one of filter type, filter strength, filter coefficients, and filter taps.

23. The method of claim 21, wherein block attributes include at least one of prediction mode, reference frame type and residual error attribute.

24. The method of claim 21, wherein determining a plurality of values of one or more loop filter attributes further comprises at least one of:

setting the plurality of values to preset default values when the frame being decoded is a key frame; and

setting at least one of the plurality of values to the value specified in the frame being decoded if the frame being decoded specifies that the value should be updated.

25. The method of claim 22, wherein selecting one of the plurality of values of one or more loop filter attributes for a particular block based on that block'"'"'s block attributes further comprises:

determining a baseline loop filter attribute value as specified in at least one frame;

determining one or more preset incremental values based on the block'"'"'s block attributes; and

adding the one or more preset incremental values to the baseline loop filter strength value to compute the value of at least one loop filter attribute.