Method and apparatus for generating a digital facsimile signal

Abstract

A facsimile transmitter detects dark-light variations in an illuminated document by means of a photodetector. After amplification, the output from the photodetector is applied to a threshold detector generating a multilevel digital signal. When the magnitude of the amplified photodetector signal is greater than one fixed threshold level, one level of the digital signal is generated. When the magnitude of the amplified photodetector signal is less than another fixed threshold level, another level of the digital signal is generated. When the magnitude of the amplified photodetector output lies between the two threshold levels, one level of the digital signal is generated when the peaked, amplified photodetector signal is greater than the unpeaked amplified photodetector signal and the other level of the digital signal is generated when the peaked amplified photodetector signal is less than the unpeaked, amplified photodetector signal. The threshold detector output is utilized to control a carrier modulator which generates signals for transmission to a remotely located receiver through a communications link.

Dependencies are inferred from the claim text.