Single-Frame Prediction for High Video Compression

In this abstract, we present a novel technique to encode video sequences, that performs a region-based motion compensation of each frame to be encoded so as to generate a predicted frame. The set of regions to be motion compensated for a given frame has been obtained through a quadtree segmentation of the motion field estimated between a single reference frame (representing a typical projection of the scene) and the frame to be encoded. This way, no DPCM loop in the temporal domain is introduced, avoiding the feedback of the quantization errors. Under the assumption that the projection of the scene on the image plane remains nearly constant, only slight deformations of the reference frame occur from one frame to the next, so that very limited information needs to be coded: (1) the segmentation shape; (2) the motion information. Temporal correlation is used to predict both types of information so as to further reduce any left redundancy. As the segmentation may not be perfect, spatial correlation may still exist between neighboring regions. This is used in the strategy designed to encode the motion information. The motion and segmentation information are estimated on the basis of a two stage process using the frame to be encoded and the reference frame: (1) a hierarchical top-down decomposition, followed by (2) a bottom-up merging strategy. This procedure can be nicely embedded in a quadtree representation, which ensures a computationally efficient but rather robust segmentation strategy. We show how the proposed method can be used to encode QCIF video sequences with a reasonable quality at a 10 frame/s rate using roughly 20 kbit/s. Different schemes for prediction are compared pointing the advantage of the single reference frame for both prediction and compensation.