Pixel-based averaging predictor for HEVC lossless coding

This paper presents an intra-frame prediction scheme designed for lossless coding using HEVC. The proposed coding method comprises a pixel-wise prediction based on original samples. It is realized as a separate intra prediction mode, which replaces the PLANAR mode. In order to perform the prediction, a four-sample template around the pixel that is to be predicted is compared to the respective template of a four-pixel neighborhood. For each reference template, the sum of absolute differences (SAD) is determined. A table look-up of the SAD value gives the respective weighting factor for each neighborhood pixel. The predictor for the current pixel is calculated as the weighted average of the neighborhood pixels. In comparison to the unmodified HEVC Test Model HM-9.1 configured for lossless coding by disabling/bypassing transformation, quantization, and in-loop filters, the proposed method provides average bitrate savings up to 10.88% for intra-only coding at similar computational complexity.