ADAPTIVE TRANSFORM CODING OF IMAGES

Abstract

Numerous bandwidth compression techniques have been proposed in response to the continually increasing requirements for transmission and storage of high resolution imagery. Adaptive transform encoding based upon the statistics of the imagery data has proved to be very effective but introduces system complexity. An efficient adaptive encoding technique that achieves a successful compromise between complexity of implementation and performance is considered. This scheme makes use of discrete cosine transform. DCT sub-blocks are sorted into four classes according to level of image activity, measured by the total ac energy within each sub-block. Adaptivity is provided by distributing bits between classes, favouring higher levels of activity over'- lower levels. Excellent performance is demonstrated- in terms of mean square error and direct comparison of original and reconstructed images. Results are presented for various bit rates ranging from 0.4 to 1.75 bits/pixel. Tn every case the total bit rates include all overhead required for image reconstruction..