Selective intra prediction in HEVC planar and angular modes for efficient near-lossless video compression

Abstract

In the lossless mode of HEVC (high efficiency video coding), the coding gains of sample-based prediction algorithms are always better than the conventional block-based predictions within the HEVC anchor. Both block based and sample-based prediction strategies select the best prediction mode for the current prediction unit (PU), on the basis of a cost function evaluated at the PU level. Hence, the selected prediction mode for a PU may not be generating the best prediction at the pixel level. If the selection of the best prediction mode can be performed at the pixel level, the accuracy of prediction can be increased significantly. In this work, we propose two selective intra prediction strategies (SIP) which select the best prediction mode from the block-based and sample-based predictions at the pixel level. In the proposed SIP-A algorithm the SIP strategy is applied to only angular prediction modes while the combined SIP algorithm (SIP-C) employs the SIP strategy in both the angular and planar prediction modes. The proposed SIP-C algorithm enhances the performance of the current state of the art SIP algorithm in the literature by introducing better prediction strategies for both angular and planar predictions of HEVC intra prediction. To avoid the enormous overhead required to convey the choice of prediction from the encoder to the decoder, SIP algorithms utilise the least significant bit (LSB) piggybacking strategy. The experimental results provide significant improvements in coding gain and run time for the proposed near-lossless SIP algorithms.