A hybrid coding method for digital HDTV

Digitally transmitted video images suffer from sudden degradation in picture quality at high channel noise levels. This is due to the variable length coding and the large synchronization blocks used. To remedy that, we propose encoding the DCT coefficients by a hybrid fixed and variable length coding compression scheme. This method improves the compression ratio by approximately 20% and increases the system´s resistance to channel errors. To fortify the transmitted bits against channel noise we then use a synchronization method which restricts the effects of an error to a 32×16 pixel picture block. The resulting combined scheme (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