Method and apparatus of adaptive loop filtering

Patent metadata

Field	Value
Publication number	US-9813738-B2
Application number	US-201113216242-A
Country	US
Kind code	B2
Filing date	Aug 24, 2011
Priority date	Oct 5, 2010
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

A method and apparatus for processing in-loop reconstructed video using an in-loop filter is disclosed. In the recent HEVC development, adaptive loop filtering (ALF) is being adopted to process in-loop reconstruction video data, where ALF can be selectively turned ON or OFF for each block in a frame or a slice. An advanced ALF is disclosed later that allows a choice of multiple filter sets that can be applied to the reconstructed video data adaptively. In the present disclosure, pixels of the in-loop reconstructed video data are divided into a plurality of to-be-filtered regions, and an in-loop filter from a filter set is determined for each to-be-filtered region based on a rate-distortion optimization procedure. According to one embodiment of the present invention, computation of cost function associated with the rate-distortion optimization procedure is related to correlation values associated with original video data and the in-loop reconstructed video data. Furthermore, the correlation values can be shared by the multiple candidate filters during the rate-distortion optimization procedure for said each to-be-filtered region. In another embodiment, the correlation values can be shared by multiple candidate to-be-filtered regions of an area of the in-loop reconstructed video data during the rate-distortion optimization procedure for the area of the in-loop reconstructed video data.

First claim

The invention claimed is:

1. A method for processing de-blocked reconstructed video, the method comprising:
deriving de-blocked reconstructed video data from coded video data by applying a de-blocking filter to reconstructed video data comprising video data that was previously encoded;
dividing pixels of the de-blocked reconstructed video data into a plurality of to-be-filtered regions, wherein the to-be-filtered regions are formed by dividing the de-blocked reconstructed video data into equal-sized blocks until the blocks of all rows of a picture are of equal size or until the blocks of all of the rows of the picture are of equal size except for the blocks of the last row;
for each of the to-be-filtered regions,
calculating a set of correlation values of pixels for the respective to-be-filtered region, and
determining an in-loop filter from a filter set comprising an edge offset filter and a band offset filter for the respective to-be-filtered region, wherein the in-loop filter is determined from the filter set according to a rate-distortion optimization procedure, wherein values of a distortion or cost function associated with the rate-distortion optimization procedure are calculated based on filter parameters of different candidate filters in the filter set and the calculated set of correlation values for the respective to-be-filtered region shared b the candidate filters; and

applying the determined in-loop filters to the to-be-filtered regions to generate filtered regions.

2. The method of claim 1 , wherein the de-blocked reconstructed video data corresponds to de-blocked signal, or ALF (Adaptive Loop Filter) processed signal of the reconstructed video data.

3. The method of claim 1 , wherein the correlation values are associated with original video data and the deblocked reconstructed video data.

4. The method of claim 1 , wherein the correlation values are associated with original video data, prediction signal and recovered prediction error.

5. The method of claim 1 , further comprising a step of incorporating information of the in-loop filter in video bitstream.

6. The method of claim 1 , wherein the values of the distortion or cost function associated with the rate-distortion optimization procedure are calculated without applying the candidate filters in the filter set to the de-blocked reconstructed video data.

7. The method of claim 1 , wherein the in-loop filter is determined from the filter set according to the rate-distortion optimization procedure, and the rate-distortion optimization procedure is related to a modified distortion, wherein the modified distortion is derived from the distortion by removing a fixed term.

8. The method of claim 7 , wherein cost function associated with the rate-distortion optimization procedure is related to the modified distortion.

9. The method of claim 1 , wherein dividing pixels of the de-blocked reconstructed video data into the plurality of to-be-filtered regions is based on classification of the pixels of the de-blocked reconstructed video data according to intensity of the pixels.

10. The method of claim 1 , wherein a flag is used to indicate whether an edge intensity feature is used as a classifier for dividing the to-be-filtered regions.

11. The method of claim 1 , wherein the equal-sized to-be-filtered regions are adaptively merged according to the rate-distortion optimization process, wherein the rate-distortion optimization process computes costs associated with individual regions and the merged regions for all candidate filters in the filter et.

12. An apparatus for processing de-blocked reconstructed video, the apparatus comprising one or more electronic circuits configured to:
derive de-blocked reconstructed video data based on coded video data by applying a de-blocking filter to reconstructed video data comprising video data that was previously encoded;
divide pixels of the de-blocked reconstructed video data into a plurality of to-be-filtered regions, wherein the to-be-filtered regions are formed by dividing the de-blocked reconstructed video data into equal-sized blocks until the blocks of all rows of a picture are of equal size or until the blocks of all of the rows of the picture are of equal size except for the blocks of the last row;
for each of the to-be-filtered regions,
calculate a set of correlation values of pixels for the respective to-be-filtered region, and
determine an in-loop filter from a filter set comprising an edge offset filter and a band offset filter for the respective to-be-filtered region, wherein the in-loop filter is determined from the filter set according to a rate-distortion optimization procedure, wherein values of a distortion or cost function associated with the rate-distortion optimization procedure are calculated based on filter parameters of different candidate filters in the filter set and the calculated set of correlation values for the respective to-be-filtered region shared by the candidate filters; and

apply the determined in-loop filters to the to-be-filtered regions to generate filtered regions.

13. The apparatus of claim 12 , wherein the de-blocked reconstructed video data corresponds to de-blocked signal of the reconstructed video data.

14. The apparatus of claim 12 , wherein the correlation values are associated with original video data and the de-blocked reconstructed video data.

15. The apparatus of claim 12 , wherein the correlation values are associated with original video data, prediction signal and recovered prediction error.

16. The apparatus of claim 12 , said one or more electronic circuits are further configured to incorporate information of the in-loop filter in video bitstream.

17. The apparatus of claim 12 , wherein the equal-sized to-be-filtered regions are adaptively merged according to the rate-distortion optimization process, wherein the rate-distortion optimization process computes costs associated with individual regions and the merged regions for all candidate filters in the filter set.

Assignees

• Tsai Chia-Yang
• Fu Chih-Ming
• Chen Ching-Yeh
• Huang Yu-Wen
• Lei Shaw-Min
• Hfi Innovation Inc

Inventors

• Tsai Chia-Yang
• Fu Chih-Ming
• Chen Ching-Yeh
• Huang Yu-Wen
• Lei Shaw-Min

Classifications

• H04N19/439

  using cascaded computational arrangements for performing a single operation, e.g. filtering · CPC title

• H04N19/117

  Filters, e.g. for pre-processing or post-processing (sub-band filter banks H04N19/635) · CPC title

• H04N19/182

  the unit being a pixel · CPC title

• H04N19/176

  the region being a block, e.g. a macroblock · CPC title

• H04N19/17

  the unit being an image region, e.g. an object · CPC title