Achieving optimal rate-distortion performance in arbitrarily-shaped transform coding

In this paper, we present a simple but effective method to enhance the coding performance of shape-adaptive DCT (SA-DCT). By choosing the first processing direction (between horizontal and vertical) within each boundary block for doing the 1D transform, the proposed method guarantees to achieve optimal rate-distortion results and actually outperforms the existing SA-DCT algorithms significantly. The proposed method is also applicable to arbitrarily-shaped coding based on some padding techniques.