Spatial intra prediction has been added recently to the latest video coding standard H.264/AVC. In the intra prediction of H.264/AVC, there are 9, 9 and 4 prediction modes for 4×4, 8×8 and 16×16 blocks, respectively. Prediction signals are generated by using one or several reference pixels. The value of a reference pixel is copied as the prediction value. In some prediction modes, we calculate a weighted mean by averaging several pixels. The same prediction value is copied to several of the pixels lying in the prediction direction. However, if original image has patterns like gradations, the residual energy could increase which would result in low coding efficiency. In this paper, we propose a new intra prediction that generates prediction signals with a spatial gradient to deal with this problem. Simulation results show that it improves the picture quality and reduce the bit-rate by about 0.14 dB and 1.0 % on average for CIF sequences, respectively. It is also confirmed that our method is effective at high bit-rates.
Standardization of a new video coding standard, HighEfficiency Video Coding (HEVC version 1), has been completed and its compression ratio is twice as much as that of H.264/AVC under the condition of the same subjective quality. In HEVC, many coding tools contribute to the improvement of the coding efficiency. One example is the intra angular prediction mode that has finer prediction directions compared to H.264/AVC. In this paper, we propose two modified intra angular prediction methods: (A) reference pixels that are closer to the predicted pixels than the original reference pixels are exploited, and (B) a blending filter similar to the filter used in the intra DC mode is enhanced and applied. In the proposed method, the predicted signals of the angular prediction mode are generated by blending the predicted signals of the selected angular prediction mode and those of the other mode which has the opposite prediction direction. The overall average coding gain against the HM9.0.1 RExt 1.0 anchor was about 0.5% for the combined method. The maximum coding gain was about 1.0%. The average encoding and decoding run-times were 104.1 % and 103.4%, respectively.
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