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High Performance Deartifacting Filters in Video Compression

Summary

Image and video coding standards, such as JPEG, H.264/AVC, are widely used in industry. In these standards, block-based transforms are employed to compact signal energy. The transform coefficients are coarsely quantized. The quantization is the source error that causes coding artifacts, such as blocking and ringing artifacts. Non-local Kuan’s (NLK) filter was developed to restore the original coefficients from the quantized ones and it has achieved state-of-the-art performance on image postprocessing. Video compression standard H.264/AVC uses motion-compensated prediction and quantization is performed on the prediction residual of Integer Cosine Transform (ICT) coefficients. There are two main approaches in integrating deartifacting filters into video codec: post filters and in-loop filters. In-loop filters operate within the coding loop. That is, the filtered frames are used as reference frames for motion compensation of subsequent coded frames. We invented two in-loop filters Quad-tree based Empirical NLK (QENLK) filter and Quad-tree based Empirical Overcomplete NLK (QEOCNLK) filter. Empirical NLK and OCNLK filters are used to restore quantized residual transform coefficients. Restored coefficients are then projected onto designed quantization constraint sets (QCS). Quad-tree based technique is used to signal block control information which are transmitted to the decoder. Then the decoder will determine which blocks are filtered. The proposed two in-loop filters achieve on average 7.58% and 9.28% bit rate reduction for CIF sequence, 11.79% and 13.27% bit rates reduction for 720p sequence, compared with H.264 High profile. Experimental results also show that coding artifacts are effectively removed and the two methods can improve the visual quality of coded sequences significantly.

Supplementary Information

Inventor: Zhang, Renqi | Cham, Wai Kuen
Priority Number: US8630356B2
IPC Current: H04N000712
US Class: 37524029 | 348488 | 37524026 | 375241 | 375242
Assignee Applicant: The Chinese University of Hong Kong
Title: High performance loop filters in video compression
Usefulness: High performance loop filters in video compression
Summary: Video loop filter e.g. dual non-local kuan loop filter and over complete non-local kaun loop filter, for use during video compression to improve performance of video coding e.g. hybrid video coding such as H.264/advanced video coding (AVC) .
Novelty: Video loop filter e.g. dual non-local kuan loop filter, for use during video compression to improve performance of e.g. H.264/advanced video coding, has integer cosine transform unit applying cosine transform to restored coefficients

Industry

ICT/Telecom

Sub Category

Image Processing

Application No.

10/ENG/388

Others

Inventor(s): Professor Wai Kuen CHAM, Department of Electronic Engineering

Patent Status: Licensing Status: US Patent Pending Available for licensing

Country/Region

Hong Kong