Low level switched model-based coder for low bit-rate applications

Switching a model-based coder to a standard transform coder during times of poor modelling can exploit the favourable attributes of an MBC whilst maintaining the image integrity. Previous investigations have employed switching where the entire frame is interchanged between a modelled image and an H.261 coded image according to a bit-rate/quality metric. This contribution explores the use of switching only in selected regions at a macroblock level and demonstrates that the subjective quality and PSNR are improved, particularly for scenes containing large translational and rotational motion.