Influence of Image Segment Size on Efficiency of SA DCT

In the paper influence of segments size on the efficiency of SA DCT is analyzed. Namely, it is shown that typical in image compression 8times8-pixel blocks are usually too small for obtaining the best PSNR values. Optimal block size depends on compression ratio, it grows from 12times12 pixels for low compression (more than 1 bit per pixel) up to 32times32 pixels or natural (non-rectangular) segmentation for less than 0.5 bits per pixel. The explanation is obvious, it is required that for a segment at least its DC component should be computed, while the number of blocks is inversely proportional to their size. The difference is also clearly seen when evaluating images subjectively