Adaptive quantization by soft thresholding in HEVC

The High Efficiency Video Coding (HEVC) reference encoder includes a Uniform Reconstruction Quantization (URQ) method. This block level quantization technique does not take into account the importance of transform coefficients in terms of signal reconstruction. In this paper, we present a transform coefficient level quantization technique based on a soft thresholding approach, in which the quantization parameter (QP) of a transform coefficient is altered according to its importance in the signal reconstruction process and according to the overall energy of the corresponding Transform Block (TB). The proposed method attains important coding efficiency performance gains as measured by the Bjøntegaard Delta Bitrate metric (BD-Rate). In comparison with reference encoder HM 16, our technique produces both luma and chroma BD-Rate improvements in all JCT-VC test sequences, particularly for sequences in Class E using the Low Delay B and Low Delay P configurations, with BD-Rate reductions of up to 5.5% (Y), 13.2% (Cb) and 11.7% (Cr).