Lifting-Based Directional DCT-Like Transform for Image Coding

Traditional 2D DCT implemented by separable 1D transform in horizontal and vertical directions does not take image orientation features in a local window into account. To improve it, we propose to introduce directional primary operations to the lifting-based DCT and thereby derive a new directional DCT-like transform. A JPEG-wise image coding scheme is also proposed to evaluate the performance of the proposed directional DCT-like transform. In this scheme, each 8times8 block can be transformed along different direction in order to better adapt to local orientation properties of image. The experimental results show that the performance of the proposed directional DCT can dramatically outperform the conventional DCT up to 2 dB even without modifying entropy coding.