CONVERSION TO A TWO-VALUED VIDEO SIGNAL

A system for converting an analog video signal obtained by scanning an original image to be processed into a two-valued video signal such as an input portion of a facsimile machine includes a peak/valley extracting circuit for extracting peaks and valleys in the analog video signal before thresholding the analog video signal so as to determine an optimal threshold level to be used in thresholding. The peak/valley extracting circuit includes peak and valley thresholds in addition to the threshold to be used in thresholding the analog video signal to produce a two-valued video signal. The peak/valley extracting circuit is so structured to supply a peak/valley extraction signal if an extracted peak or valley also satisfies the condition that it is equal to or higher or lower in level than the peak or valley threshold.