Patrick Devaney

Segmentation-based image compression for video cassette recorders

Studio-quality video cassette recorders used for editing need intraframe compression schemes that can compress/decompress an image many times without appreciable degradation. They also require fast-forward playback of a low-quality image using only a small part of the compressed data. A system with these features is reported, based on image segmentation. A segmented approximation to the original image is losslessly encoded and a residual image is created. The lossless coding scheme is motivated by examining the constraints caused by channel errors and trick play modes. The residual image is coded by a conventional data compression technique. By preserving the main image features with a lossless code, the multi- generation performance is stabilized. Because segmentation is shift-invariant, edits that include x-y shifting between generations do not degrade performance. This paper reports a new segmentation algorithm. It has high resolution, obtained in part by a newly designed edgeness measurement. Using this, images are segmented to pixel accuracy by an algorithm which is only O[n] in complexity. Multi-generation simulations of sequences with 4:1 compression ratios are presented at both normal and shuttle speeds, using both sub-band and DCT residual coders.