Variable block-size image coding

Current algorithms for the efficient coding of images generally employ one of two techniques: Vector Quantization or Transform Coding. Both of these methods are based on block coding, and the traditional algorithms require the partitioning of the original image into a number of, usually square, regions of uniform size. This paper explores techniques where the size of these regions, or blocks, is varied according to the local detail of the image. By isolating regions of differing detail, using a quad-tree based segmentation algorithm to control the size of the blocks, the low detail areas can be encoded at substantially lower rates than is otherwise possible. Satisfactory quality coding results are achieved at rates between 0.35 and 0.4 bpp; the actual rate depends on the image being encoded.