Improving Intra mode coding in H.264/AVC through block oriented transforms

In an H.264 video encoder, the important task of intra coding is performed in the residual domain after a spatial transform has been applied to the block data. Although the intra prediction is very efficient and shows the ability to capture some orientations of the image, after this spatial prediction the intra residual may still show regular structures. To take this possible regularity into account, especially orientation, we propose a preprocessing stage that selects the best rotation to be applied to the block among a set of predefined rotations. To this end, we utilize a rate-distortion algorithm. We further propose to calculate the real orientation of the block to decrease the amount of computation. Experimental results show that compared to the standard intra-prediction mode of H.264, the proposed method can gain up to 1 dBs