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The rapid development of wired and wireless networks tremendouslyfacilitates communications between people. However, most of thecurrent wireless networks still work in low bandwidths, and mobiledevices still suffer from weak computational power, short batterylifetime and limited display capability. We developed a very lowbit-rate bi-level video coding technique, which can be used invideo communications almost anywhere, anytime on any device. Thespirit of this method is that rather than giving highest priorityto the basic colors of an image as in conventional DCT-basedcompression methods, we give preference to the outline features ofscenes when we have limited bandwidths. These features can berepresented by bi-level image sequences that are converted fromgray-scale image sequences. By analyzing the temporal correlationbetween successive frames and flexibilities in the scenepresentation using bi-level images, we achieve very high ratioswith our bi-level video compression scheme. Experiments show thatin low bandwidths, our method provides clearer shape, smoothermotion, shorter initial latency and much cheaper computational costthan do DCT-based methods. Our method is especially suitable forsmall mobile devices such as handheld PCs, palm-size PCs and mobilephones that possess small display screens and light computationalpower, and work in low bandwidth wireless networks. We have builtPC and Pocket PC versions of bi-level video phone systems, whichtypically provide QCIF-size video with a frame rate of 5-15 fps fora 9.6 Kbps bandwidth.

As the Internet and wirless networks are developed rapidly, the demand of communicating anywhere, anytime on any device emerges. However, most of the current wireless networks still work in low bandwidths, and mobile devices still suffer from weak computational power, short battery lifetime and limited display capability. We developed portrait video phone systems that can run on Pcs and Pocket Pcs at very low bit rates through the Internet. The core technology that portrait video phones employ is the so-called portrait video (or bi-level video) codec. Portrait video codec first converts a full-color video into a black/white image sequence and then compresses it into a black/white portrait-like video. Portrait video processes clearer shape, smoother motion, shorter initial latency, and cheaper computational cost than MPEG2, MPEG4 and H.263 for low bandwidths. Typically the portrait video phone provides QCIF-size video with a frame rate of 5-15 fps for a 9.6 Kbps video bandwidth. The portrait video is so small that it can even be transmitted through an HTTP proxy as text. Experiments show that the portrait video phones work well on ordinary GSM wireless telecommunication networks.