ENHANCEMENT OF IMAGE QUALITY FOR LOW BIT RATE VIDEO CODING

CCITT Recommendation H.261 on coding for visual telephony is applicable to bit rates of p X 64 kbits/s, where p = 1,2,..., 30. It generally performs well over the intended bit rates. However, at the very low rates of 64 and 128 kbits/s, it suffers from visual degradation due to coarse quantization. In this paper, we studied the various approaches or combinations of them to improve the image quality. Methods studied include reducing the quantizer step size, randomized scanning of the macroblocks, and/or nonuniform quantization of the transform coefficients.