Telecopier transmitter with automatic contrast control - compares photoelectric signal with reference and amplifies it to preselected level in preamplifier

摘要

In the telecopier the dynamic range of a photoelectric signal produced by scanning a document the information on which is to be transmitted is compared with a reference and amplified to a preselected level in a preamplifier. The signal is then applied to a contrast control circuit which adjusts the mean value of the signal. The signal amplitude is also adjusted where necessary to maintain the dynamic range of the signal within preset limits. This ensures that when received and decoded the various greys of the reproduced document compare favourably with the transmitted document information.