Context-based adaptive variable length coding of transform coefficients

摘要

In image and video coding VLC (Variable Length Coding) technique for transformed coefficients is widely adapted to reduce statistical redundancy. Each value of coefficients is assigned to a code-number by referring to a look-up table, and a variable length code is assigned to each code-number. Coding efficiency of VLC depends on the structure of the look-up table that should be suitable for the look-up table that should be suitable for the appearance probability of the coefficient values. In this paper, we propose a new VLC method that updates the look-up table adaptively to match the appearance probability of the transformed coefficients. This method has two techniques: context-based table optimization and inverse order scanning. We apply the proposed method to H.264/AVC codec, and confirm that the proposed method can improve coding efficiency about 5%.