Context-Based Adaptive Variable Length Coding based Compression Scheme for Images

In order to achieve a high compression ratio, the Context-Based Adaptive Variable Length Coding (CBAVLC) standard has incorporated a large number of coding modes which must be evaluated during the coding process to determine the optimal rate-distortion trade-off. The coding gains of CBAVLC arise at the expense of significant coder complexity. One coder process that has been identified as having potential for achieving computation savings is the selection between skipping the coding of a macro block and coding of the macro block in one of the remaining coding modes. In low contrast images, a large percentage of macro blocks are “skipped”, that is, no coded data are transmitted for these macro blocks. By estimating and identifying macro blocks to be skipped during the coding process, significant savings in computation can be realized, since the coder then does not evaluate the rate-distortion costs of all candidate coding modes. The proposed scheme shows that this approach can result in a time savings of over 80% for lowcontrast images at a negligible decrease or, in certain cases, a slight increase in quality over a reference codec.