Designing a videocodec involves a four-way tradeoff among computational complexity, data rate, picture quality, and latency, Rapid advancement in very large-scale integration technology has provided CPU's with enough power to accommodate a software-only videocodec, Accordingly, computational complexity has resurfaced as a major clement in this tradeoff. With a view toward significantly reducing computational complexity relative to standards-based videocodecs, we introduce a pixelwise conditional differential replenishment scheme to compress video via perception-sensitive decomposition of difference frames into a facsimile map and an intensity vector. Our schemes, which apply techniques from facsimile, are transform free. Some of them also involve no motion compensation and hence are completely free of block-based artifacts and particularly computationally economical, The fusion of our facsimile-based video-coding schemes and spatio-temporal perceptual-coding techniques facilitates powerful software-only video conferencing on today's medium- and high-end personal computers. Indeed, assuming that a frame-capture driver has been provided, our motion-compensation-free approach has yielded a software-only, full-duplex, full-color videoconferencing system that conveys high-quality, CIF/Q-NTSC-sized video at 30 frames per second on 200-MHz Pentium PC's sending less than 300 Kbps in each direction, We also present new spatio-temporal compression techniques fur perceptual coding of video. These techniques, motivated by the classical psychological experiments that led to formulation of the Weber-Fechner law, allow videocodec systems to capitalize on properties of the human visual system. Some of our spatiotemporal perceptual techniques not only apply to our proprietary pixelwise conditional differential replenishment schemes that we describe For video conferencing but also can readily be incorporated into today's popular video standards.
