Hybrid video coding for low bit-rate applications

This paper proposes a hybrid DCT/quadtree coding technique to compress motion compensated difference (MCD) images for video conferencing applications. The hybrid scheme is developed primarily to eliminate the visually annoying "corona" effect caused by the traditional DCT coding of subimage blocks containing edge components. In this coding framework, the quadtree segmentation scheme is selected to compress edge blocks because of its ability to describe geometrical structures accurately. For quadtree coded blocks, each segmented subregion is represented by its associated sample mean, which is quantized and transmitted along with the segmentation pattern information to the receiver for reconstruction. The remaining subimage blocks are coded using the DCT. Simulation results demonstrate that this hybrid coding system provides a subjectively superior video quality than traditional DCT coding systems: the corona effect is significantly reduced and the visible difference is most noticeable at low bit rates. >