JPS57203179A - Initial value setting circuit for white level follower - Google Patents

Abstract

PURPOSE:To set easily an initial value at the leading edge of a form, by selecting the maximum value of a white level following width as the reference of quantization and quantizing a picture input signal with a rough gradation of a white level follower and comparing a white level initial value with the current picture signal. CONSTITUTION:The electric signal obtained from a photoelectric transducer 4 by scanning of a form 2 is applied to an A/D converter 11 and is compared with a white reference level, and its binary signal is applied to an encoder 12. A prescribed bit multilevel signals encoded by this encoder 12 is applied to one input of a following circuit 13, and the current white level stored in a memory 15 is inputted to the other input of the circuit 13, and a new white level is determined in the circuit 13 on a basis of these two inputs. In this case, the input signal has a limited value which follows a small change of the white level and is increased by +1 or decreased by -1 for a large change of the white level or appearance of black in accordance with a prescribed algorithm, thus generating a white level accurately. The output of the circuit 13 is applied to a memory 14 and a converting circuit 16 through a register 14.