A hybrid coding method for digital HDTV signals

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 lengths compression scheme. This method improves the compression ratio by approximately 20% and increases the system´s resistance to channel errors. We then combine this hybrid algorithm with an error protected synchronization method which uses small blocks of size 32×16 pixels. The resulting combined schemes 1) significantly improve the error resistance characteristic of the system, 2) eliminate the abrupt picture degradation, and 3) does not alter the original data transmission rate