1. An image processing circuit of an image input device which performs a predetermined image processing of an image photographed by an image pickup device in said image input device, said circuit comprising: a real time processing unit configured to sequentially input a pixel data in the image photographed by said image pickup device and configured to perform a predetermined general image processing of the pixel data by real time processing; a main memory that stores a pixel data outputted from at least said real time processing unit, in image frame units; a central control unit configured to execute exceptional image processing as a software program processing with respect to the pixel data stored in said main memory; said real time processing unit includes a selector configured to select one of said pixel data in the image photographed by said image pickup device and said pixel data stored in said main memory; said pixel data outputted from said real time processing unit and said pixel data stored in said main memory include four color component data and each of the components in the four color component data includes a predetermined data length; and said selector is further configured to select only one component of the four color component data as a selected color component and selectively output and store the selected color component in said main memory.