CORRELATION ANALYSIS OF DISCRETE COSINE TRANSFORM COEFFICIENTS OF IMAGE BLOCKS

Abstract

Task of lossy image compression based on discrete cosine transform (DCT) is considered. For image blocks having size 8x8 pixels (it corresponds to division of images on blocks in JPEG standard) presence of correlation between different DCT coefficients of the same block as well as between coefficients of different blocks is analyzed. Values of correlation coefficients are calculated and averaged for set of test images. It is shown that there is substantial correlation between absolute values of DCT coefficients of the same block, while correlation between signs of the coefficients is insignificant. It is shown also that correlation between DCT coefficients of adjacent blocks is smaller than the one for coefficients of the same block. At the same time there are noticeable correlations not only for absolute values but also for signs of coefficients. It is shown that position of DCT coefficient with maximum correlation with given coefficient can be effectively predicted using its indices.

Keywords

• дискретне косинусне перетворення, коефіцієнт кореляції пірсона, стиснення трафіку, стиснення зображень з втратами, jpeg.