Enhancement of image quality for low bit rate video coding

The authors propose a number of improvements based on the RM8 algorithm aimed at enhancing the visual quality of the reconstructed images, especially at the low rates of 64 and 128 kb/s. RM8 is a novel approach to defining a coding standard for video communications at p ×64 kb/s. Methods studied include reducing the quantizer step size, randomized scanning of the macroblock, and/or nonuniform quantization of the transform coefficients. Reducing the quantizer step size did improve the codec performance, but only marginally. Nonuniform quantization coupled with randomized scanning of the macroblocks was found to be effective in improving the image quality, both objectively and subjectively. Improvement is particularly marked in the initial 20 frames of a sequence