shie - deingu amendment manner and its device null which prevent the influence of noise

摘要

PURPOSE:To prevent the occurrence of a noise and the deterioration of a picture quality by making a picture signal and a shade correction signal be different levels at a timing except the effective period of the picture signal. CONSTITUTION:The picture signal obtained by an image pick-up element 17 is converted into a digital signal in an A/D converter 19 via a buffer 18, and is written in a 1-line memory 20 as a reference voltage, and is used as a first reference voltage for the A/D conversion of the picture signal of a subsequent original. A reference voltage switching circuit 21, in the case of the A/D conversion of the information of a reference density plats 10, impresses a full-scale value from a full-scale generating source 22 on the A/U converter 19 through a D/A converter 23 as a second reference voltage, and in the case of the A/D conversion of the picture signal, impresses the first reference voltage stored in the 1-line memory 20 on the A/D converter 19 via the D/A converter 23. Thus, the occurrence of the noise is prevented and the picture quality is improved.