Method and apparatus for video coding using adaptive loop filter

• US 8,897,591 B2
• Filed: 11/29/2012
• Issued: 11/25/2014
• Est. Priority Date: 09/11/2008
• Status: Active Grant

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: Google Inc. (Alphabet Inc.)
• Inventors: Wilkins, Paul, Bankoski, James, Xu, Yaowu
• Primary Examiner(s): Chu, Randolph I
• Application Number:
  US13/688,608
• Publication Number:
  US 20130114679A1
• Time in Patent Office: 726 Days
• Field of Search: None
• US Class Current: 382/268
• 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

Methods for reducing blocking artifacts at the boundary between adjacent blocks reconstructed from a frame of compressed video information are disclosed herein. The frame includes a prediction stage parameter and a residual error attribute with respect to at least one of the blocks. One method includes reconstructing the at least one block based on the prediction stage parameter and the residual error attribute, categorizing the at least one reconstructed block into one of a plurality of categories based on the prediction stage parameter and the residual error attribute, identifying a filter strength value for the category in which the at least one reconstructed block is categorized based on at least one of the prediction stage parameter or the residual error attribute associated with that category, and filtering the boundary adjacent to the at least one reconstructed block using the identified 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 and a residual error attribute with respect to at least one of the blocks, the method comprising:

reconstructing the at least one block based on the prediction stage parameter and the residual error attribute;

categorizing the at least one reconstructed block into one of a plurality of categories based on the prediction stage parameter and the residual error attribute;

identifying a filter strength value for the category in which the at least one reconstructed block is categorized based on at least one of the prediction stage parameter or the residual error attribute associated with that category; and

filtering the boundary adjacent to the at least one reconstructed block using the identified 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 the residual error attribute is one of a null motion vector and a non-zero motion vector.

6. The method of claim 1, wherein identifying the filter strength value further comprises:

identifying one or more filter modifiers for the category in which the at least one reconstructed block is categorized based on at least one of the prediction stage parameter or the residual error attribute associated with that category; and

computing the filter strength value based on a baseline filter strength and the one or more filter modifiers.

7. The method of claim 6, wherein the one or more filter modifiers are identified at the frame level.

8. The method of claim 7, further comprising:

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

wherein at least some of the filter modifiers are set to a default value if the frame being decoded is a key frame.

9. 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, the method comprising:

categorizing the blocks of at least one of the frames into categories based on both the prediction stage parameter and the residual error attribute associated with each given block;

determining a filter strength value for each of the categories;

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

10. The method of claim 9, wherein the prediction stage parameter includes at least one of a reference frame type or a prediction mode.

11. The method of claim 10, wherein the reference frame type is one of intra-frame, last frame, golden frame and alternate reference frame.

12. The method of claim 10, wherein the prediction mode is one of non-split mode and split mode.

13. The method of claim 10, wherein the residual error attribute is one of a null motion vector and a non-zero motion vector.

14. The method of claim 9, wherein determining the filter strength value includes:

adding, for each of the categories, one or more filter modifiers to a baseline filter strength value.

15. The method of claim 14, wherein the one or more filter modifiers are determined based on delta values specified in at least one of the frames.

16. The method of claim 14, further comprising:

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

wherein at least some of the filter modifiers are set to a default value if the frame being decoded is a key frame.

17. An apparatus for reducing blocking artifacts at the boundary between adjacent blocks reconstructed from a frame of compressed video information that includes a prediction stage parameter and residual error attribute with respect to at least one of the blocks, the apparatus comprising:

means for reconstructing the at least one block based on the prediction stage parameter and the residual error attribute;

means for categorizing the at least one reconstructed block into one of a plurality of categories based on the prediction stage parameter and the residual error attribute;

means for identifying a filter strength value for the category in which the at least one reconstructed block is categorized based on at least one of the prediction stage parameter or the residual error attribute associated with that category; and

means for filtering the boundary adjacent to the at least one reconstructed block using the identified filter strength value.

18. The apparatus of claim 17, wherein the prediction stage parameter includes at least one of a reference frame type and a prediction mode.

19. The apparatus of claim 18, wherein the reference frame type is one of intra-frame, last frame, golden frame and alternate reference frame and the prediction mode is one of non-split mode and split mode.

20. The apparatus of claim 17, wherein the filter strength value is identified at the frame level.