Very low bit rate video coding using H.263 coder
Recently, ITU-T established a draft standard, H.263 to he used as a possible standard for very low bit rate video coding at less than 64 kb/s. It is based on the ITU-T H.261 standard for videoconferencing. This paper provides an analysis of the performance of H.263 coder with the aim of establishing its operational parameters and limitations when operating at very low bit rates. Its performance is then optimized by selecting the desired set of operational parameters. The H.263 coder suffers from "blocking" effects when operating at very low bit rates. To improve the subjective quality of the coded images, the discrete cosine transform (DCT) coefficients are weighted using a visual quantization matrix before quantization. Simulation results showed that the proposed method increases the peak signal-to-noise ratio (PSNR) values at all bit rates tested, but more importantly, the perceived visual quality is improved significantly by reducing the annoying "blocking" effects.