ADAPTIVE BINARY STATE DECISION SYSTEM

Means for quantizing the continuously varying analog signal output of a facsimile photodetector into a two level binary signal respectively characteristic of detailed black and white areas of a sheet being scanned. The quantizing means provides for later compression of the binary signal by limiting the level shifts in the binary signal to occur only when the analog signal clearly represents a change to the opposite characteristic as determined when the analog signal crosses two separated threshold levels that continuously or discretely adjust in response to the levels of the analog signal representing black and white.