Methods for performing 2-dimensional maximum differences coding and decoding during real-time facsimile image compression and apparatus therefor

摘要

Compression and decompression methods for transmitting facsimile images in which the facsimile image is compressed in both vertical and horizontal directions are implemented using two dimensional maximum differences algorithms. Asymmetrical and fractional image compression are provided by controlling the number of lines, i.e., rows or columns, being compressed and by controlling the bit segment length used during each differences determination. The compressed facsimile image is decompressed by selecting a reference bit in the decompressed facsimile image and expanding the bit in both vertical and horizontal directions in accordance with a binary value of bits near the selected reference bit. A transmission channel adapted to serially perform the encoding and decoding functions is also described.