Video signal regulating apparatus

Abstract

A sensor (S.sub.1) is provided in a reflector (23) which reflects light from a lamp (21) to illuminate an original document (24) for scanning. A light image of the document (24) is scanned by an optoelectronic scanning array (28) which produces video signals corresponding thereto. The sensor (S.sub.1) is so located as to receive light both directly from the lamp (21) and reflected from the document (24) so as to produce an output signal corresponding to a combined function of the background density of the document (24) and the intensity of the lamp (21). This sensor output is used to control the amplification factor of an amplifier (29) which amplifies the video signals so as to maintain a constant average level of the output thereof. The background level is removed from the video signals by a peak hold circuit (32) and an operational amplifier (34) which subtracts the video signals from the output of the peak hold circuit (32). The peak hold circuit (32) also combine the video signals with a reference value. A variable voltage divider (37) is connected to the output of the operational amplifier (34) and is manually variable to compensate for various types of document patterns such as hairlines, handwritten characters and the like.