Generalized Zigzag Scanning Algorithm for Non-square Blocks

In the shape-adaptive compression algorithm, an image is divided into irregular regions instead of 8×8 blocks to achieve better compression efficiency. However, in this case, it is improper to use the conventional zigzag of JPEG to scan the DCT coefficients. For example, for a region whose height is M and width is N, if N is much larger than M, then the DCT coefficient in the location (0, b) is usually larger than that in (b-1, 0). However, when using the conventional zigzag method, (b-1, 0) is scanned before (0, b). In this paper, we propose new algorithms to perform coefficient scanning for irregular regions. The proposed methods are easy to implement and can obviously improve the coding efficiency of the shape-adaptive compression algorithm.