Sample-based edge prediction based on gradients for lossless screen content coding in HEVC

The amount of generated screen content sequences has recently increased due to the high popularity of multimedia services such as videoconferencing and cloud video gaming. Screen content sequences are characterized by a high number of sharp edges and repeating patterns, which are difficult to compress using current video coding tools. This paper proposes improvements to lossless compression of these sequences using HEVC intra-prediction. Specifically, the paper proposes SAP-G (sample-based angular intra-prediction with gradient-based edge prediction), which is a DPCM-based intra-prediction method that combines angular prediction with a low-complexity edge predictor and a DPCM-based DC predictor. The edge predictor, which replaces the current PLANAR mode, is based on the computation of gradients along four main directions using the adjacent pixels to the pixel to be predicted. Simulation results show that SAP-G can attain average bit-rate reductions of 15.44% over current HEVC intra-prediction for a variety of screen content sequences. Results also show that SAP-G outperforms other state-of-the-art DPCM-based intra-prediction methods without increasing encoding/decoding times.