In-loop deblocking filter for block based video coding
Blocking artifacts are inherent and inevitable phenomena at low bit rates in current block-based video coding schemes. The paper proposes a deblocking technique to reduce blocking artifacts and improve visual quality. Different from the post-processing technique adopted in MPEG-4, the proposed technique is directly applied to the reference image for effective motion prediction instead of just for display purposes. In other words, the deblocking filter is introduced into the motion compensation loop in the video coding. Because of the negative effects of the deblocking filter, such as blurring the details of the image, not every block boundary needs to be filtered. It has to be determined whether the boundaries between two blocks should be filtered or not. Therefore, we also propose a decision-making criterion based on the available motion information (vector and mode). Experimental results show that the proposed deblocking method can improve image quality both in subjective and objective aspects. It also outperforms the post-processing technique in MPEG-4.