A HYBRID CODING METHOD FOR DIGITAL HDTV

Digitally transmitted video images suffer from sudden degradation in p icture quality at high channel noise levels. This is due to the variab le length coding and the large synchronization blocks used. To remedy that, we propose encoding the DCT coefficients by a hybrid fixed and v ariable length coding compression scheme. This method improves the com pression ratio by approximately 20% and increases the system's resista nce to channel errors. To fortify the transmitted bits against channel noise we then use a synchronization method which restricts the effect s of an error to a 32x16 pixel picture block. The resulting combined s cheme 1) significantly improves the error resistance characteristic of the system, 2) eliminates the abrupt picture degradation, and 3) does not alter the original data transmission rate.