Picture signal quantizing circuit

Claim 1

A picture signal quantizing circuit for quantizing with respect to multiple levels an analog picture signal representative of a picture which is read from a document, comprising: a background level detector for detecting and holding a peak value of the analog picture signal to generate a background level voltage indicative of a background level of the document; a reference voltage generator for dividing the detected and held background level voltage to determine a highest level and a lowest level for quantization to generate a first reference voltage and a second reference voltage corresponding to the highest level and the lowest level respectively; a reference voltage divider comprising a series circuit having 2 n ladder resistors connected serially to generate different output voltages from junctions between said resistors, a first tap led out from one end of said series circuit, a second tap led out from the other end of the series circuit, and a third tap led out from a predetermined position between said first and second taps; halftone reproducibility accentuating means for, when quantizing an analog picture signal by comparing the signal with a reference voltage, non-linearly dividing the reference voltage so that a halftone portion of the analog picture signal, and thereby a halftone of a reproduced picture are accentuated; a comparator circuit comprising (2 n -1) comparators for respectively comparing the output voltages from the junctions between the resistors of the series connection with the analog picture signal; and an encoder for generating a digital signal in response to outputs of said comparators, said digital signal being an n-bit binary code; the halftone reproducibility accentuating means comprising a first resistor having a predetermined resistance and connected between the second and third taps; the resistance of the first resistor being R/2, where R is a total resistance of the series circuit of the reference voltage divider; the halftone reproducibility accentuating means further comprising a first switch connected in series to the first resistor, a second resistor connected to the first tap, a second switch connected in parallel to the second resistor, a third resistor connected between the second tap and ground, and a third switch connected in parallel to the third resistor.