Optimal variable quantization for JPEG extensions

We present optimal variable quantization techniques for the newly proposed JPEG extensions from ISO/IEC 10918-3 (ITU-T Recommendation T.84). Variable quantization for each block is necessary to transcode from any video compression format (e.g. MPEG). It also gives increased subjective quality and efficient utilization of the channel bandwidth. The selective refinement extension is useful for selecting a part of an image for further refinement. In our experiments, we compare the reconstructed image obtained by variable quantization to that of the JPEG baseline system