Boundary block-merging (BBM) technique for efficient texture coding of arbitrarily shaped object

We present an efficient texture coding method which enhances the coding efficiency of conventional discrete cosine transform (DCT) with padding techniques for arbitrarily shaped objects in object-based video coding where shape information is provided. The BBM (boundary block-merging) technique is applied to the boundary macroblocks of 16×16 pixels of a VOP (video object plane) which consist of both background and object pixels. A macroblock consists of four subblocks of 8×8 pixels. For boundary subblocks consisting of object and background pixels, padding is performed in the background region. For a pair of padded boundary subblocks in a macroblock of which alignment belongs to a predefined set, one subblock is rotated 180° and merged into another one if object pixels do not overlap. After merging, the boundary macroblock is coded using the conventional DCT coding. The merging process reduces the number of subblocks to be DCT coded, and high correlation between adjacent subblocks makes the number of DCT coding bits small. Experimentation has been done on various test sequences under different test conditions, and verifies significant coding efficiency improvement: reduction of coding bits for luminance boundary blocks by 5.7-11.9% at the same PSNR values compared with the padding-based DCT without BBM