Facsimile-based video compression method and system

Abstract

A method and system for compressing and decompressing video image data in real time employs thresholding and facsimile-based encoding to eliminate the need for computationally intensive two-dimensional transform-based compression techniques. The method operates first by forming a difference frame which contains only information pertaining to the difference between a current video image frame and a computed approximation of the video image frame. The difference frame is fed to a thresholder which categorizes each pixel in the frame as being either in a first set having intensities above or at a preset threshold, or a second set having intensities below a preset threshold. A facsimile-based compression algorithm is then employed to encode the first set of above or at threshold pixel locations. To compress the intensity data for each above or at threshold pixel, a quantizer and lossless encoder are preferably employed, with the quantizer serving to categorize the intensities by groups, and the lossless encoder using conventional coding, such as Huffman coding, to compress the intensity data further. Various techniques may be employed with the embodiments of the invention to adjust the actual amount of compressed data generated by the method and system to accommodate communication lines with different data rate capabilities.