Direction-adaptive partitioned block transform for image coding

We propose a direction-adaptive block transform that exploits the directionality in images to improve the compression performance. It can be viewed as a generalization of variable block-size transforms with the inclusion of non-rectangular partitions and directional transforms. As a block transform, it can be directly combined with block-wise intra and inter prediction in video coding standards. Experimental results show that the proposed transform outperforms the variable block-size 2-D DCT by up to 3 dB. It also outperforms a previously proposed direction-adaptive DCT by up to 2 dB. When combined with intra prediction, the proposed transform further provides a gain of 0.5 to 2 dB upon intra prediction with the 2-D DCT.