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Abstract
A color video image hybrid coder is investigated for digital picture telephony at a very low transmission rate of 64 kbit/s. At first, the coder parameters are adjusted to obtain improved performance at this data rate. To improve the efficiency further, a dual blocksize concept is introduced in the scheme. Also, a hierarchical blockmatching algorithm for improved motion estimation is employed and the motion vector components are differentially coded with an efficient variable word length coding table. Finally, the interfield correlations between predictor modes are investigated for efficient predictor mode coding. Simulation results on CCITT color video test sequences arc presented.