Block artifact deteriorates the video subjective visual quality, so it is needed to take measures to reduce the effect of block artifact. Unlike MPEG series coding system, H.264 does not use post-processing filter but adds loop-filter in motion vector compensation loop. The most essential points in loopfilter are strength- a value which indicates the strength of block artifact- and filtering operators. But loopfilter in H.264 is not so satisfactory, especially in low bitrate. A new loopfilter algorithm is proposed to improve the performance of filtering. The value of strength is evaluated by coding modes (intra and inter), estimated motion vector, flatness of image region and QP. There are 4 different filtering operators in total. Every operator which is a one-dimension filtering window corresponds a non-zero strength. The experiments show that subjective and objective quality of video can be improved remarkably.
"A new de-blocking algorithm in video coding system", Proc. SPIE 5985, International Conference on Space Information Technology, 598502 (4 January 2006); doi: 10.1117/12.655640; https://doi.org/10.1117/12.655640