Adaptive post-processing algorithms for low bit rate video signals

A new adaptive post-processing algorithm to enhance the quality of a noisy video sequence is presented. This algorithm employs motion compensated frame averaging to improve picture quality. A classification algorithm divides sub-blocks of pixels in the averaged frame into 4 classes: edge, smooth, non-smooth with motion and non-smooth without motion. Spatial algorithms that perform multilevel median filtering, double median filtering and median filtering are used for pixels belonging to edge, smooth and non-smooth with motion categories. Pixels in the nonsmooth, unmoving category are left unfiltered to preserve corresponding image texture. In a simpler version of this 4-class system, the motion cues and motion compensated frame averaging are eliminated, and the purely spatial filtering is based on a 3-class algorithm. When used at the output of a 3-D subband coder at 384 kbps, the spatial postfilter was shown to provide a consistent gain in subjectively evaluated picture quality. Twenty-five viewers participated in an experiment involving three coded sequences. In a pairwise comparison of postfiltered and unfiltered sequences, the postfiltered version was judged to be better in 63 out of 75 instances