IMPROVED CHEN-SMITH IMAGE CODER

A new transform coder based on the zonal sampling strategy, which outp erforms the JPEG baseline coder with comparable computational complexi ty, is presented. The primary transform used is the 8- x 8-pixel-block discrete cosine transform, although if can be replaced by other trans forms, such as the lapped orthogonal transform, without any change in the algorithm. This coder is originally based on the Chen-Smith coder, therefore, we call it an improved Chen-Smith (ICS) coder. However, be cause many new features were incorporated in this improved version, it largely outperforms its predecessor, Key approaches in the ICS coder, such as a new quantizer design, arithmetic coders, noninteger bit-rat e allocation, decimated variance maps, distance-based block classifica tion, and human visual sensitivity weighting are essential for its hig h performance. Image compression programs were developed and applied t o several test images. The results show that the ICS performs substant ially better than the JPEG coder.