Facsimile Coding by Skipping White

Abstract

The white block skipping (WBS) method of coding binary facsimile images consists of breaking each scan line into <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> picture-element (pel) blocks, then using "0" as the code word for all-white blocks and "1" followed by the binary pattern in the block for non-all-white blocks. In the first part of this paper, we derive (based on a first-order Markov source model) the optimum block size <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> and its corresponding minimum bit rate as functions of the average white and black run lengths of the image. In the second part of this paper, we propose a modified coding scheme where all-white scan lines are essentially skipped. This modified scheme is found to be as efficient as run length coding for transmitting texts.