Efficient HEVC intra-frame prediction using curved angular modes

Blending curved and straight lines on angular modes are proposed for intra-frame prediction in high-efficiency video coding (HEVC). All 33 angular modes in HEVC have received an offset-based displacement calculation to each predicted sample, so that the resulting prediction block models image regions with curved textures. The proposal includes a negligible overhead in the syntax elements of the encoded bitstream (up to 2.56%) to transmit the curvature parameter along with the angular mode of a predicted block. Results demonstrate increased prediction accuracy and consequent reduction in residuals. There is a fair trade-off between prediction accuracy and computational complexity even considering few curvature parameters. Further evaluations show an average reduction in Bjøntegaard delta rate of 3.19% for the HEVC test sequences.