Video Compression Using Fax Techniques

We have implemented approaches to compressing and decompressing a sequence of head-and-shoulders images that trade off the data rate, picture quality, computational complexity and latency. All these approaches are transform-free and pixel-based; some of them also involve no motion compensation and hence are free of block-based artifacts. We compare the magnitude of the intensity of each pixel site in the difference frame to a threshold. If the intensity at a pixel site is above the threshold, that pixel is a survivor; otherwise, that pixel is a casualty. We zero the intensity at each casualty pixel and leave the intensity intact at each surviving pixel. A bi-level frame is formed to represent the location map of the survivors and casualties. We gather the intensities at the surviving pixels into an intensity vector. The zeroed difference frame is therefore decomposed into a bi-level frame and an intensity vector. We modified the Group 3, Group 4 or JBIG facsimile standards to compress the bi-level frame and can achieve further compression by applying scalar quantization to each element of the intensity vector. Forming the difference frames by direct subtraction of the previous decompressed frame from the current input frame permits softwareonly realization of the compresssor and decompressor on today’s home and office computers for large(CIF or Q-NTSC) full-color formats at 30 frames per second for head-and-shoudlers video at under 1.0 Mbps with PSNR > 38db, assuming provision has been made for A/D converted camera output to be pipelined into the computer CPU in real time. Motion compensation can be used to lower the compressed bit rate at the expense of increased computational burden. This is useful for applications in which data rate is the principal limitation, such as when video is sent over POTS, ISDN, cellular or PCS.