HIGH COMPRESSION DPCM BASED SCHEME FOR PICTURE CODING.

A new gray-scale image coding technique is presented in which an extended DPCM approach has been combined with entropy coding. The technique has been implemented in a freeze-frame video conferencing system which is now operational at IBM sites throughout the world. Following image pre-processing, the two fields of the interlaced 512 by 480 pixel video frame are compressed sequentially with different algorithms. The reconstructed image quality is improved by subsequent image post-processing. The image processing and compression algorithms are described in this paper. Typical grayscale video images compress to about a half bit/pixel, the reconstructed images being almost indistinguishable from the original images.