Adaptation of Ordering Techniques for Facsimile Pictures with No Single Element Runs

Coding of two-tone facsimile pictures is gaining considerable importance. Many sophisticated algorithms which use the two-dimensional correlation present in the facsimile pictures have been developed. Most of these code the picture in such a way that an exact reproduction of the picture is possible at the receiver. Considerable bit-rate reduction is possible, however, by approximating the original picture by another picture which can be coded more efficiently than the original. Success of such schemes will depend upon the type of approximation used. Approximations that introduce the least visible distortion in the picture but reduce the bit rate significantly are the most desirable. Problems of picture modification and evaluation of their advantages for two-level facsimile signals have recently begun to receive some attention. 1 " 5 We present a simple method of picture modification and then evaluate its advantages with respect to ordering techniques. 6 Pictures 857 are modified so that runs of single "white" (="0") or "black" (="1") elements along a scan line are suppressed. At high resolution of 200 dots/inch, such a modification does not degrade the picture significantly. This preprocessing allows us to modify our earlier published ordering techniques 6 " 8 in an advantageous way by treating even and