DIGITAL IMAGE PROCESSOR

Pattern data is generated in accordance with horizontal and vertical synchronizing components of a video signal. The pattern data and the video signal are stored in a memory. The video signal is written in an effective image period, while pattern data is written in other periods. Write and read addresses for the memory are generated in accordance with the horizontal and vertical synchronizing components of the video signal. Thus, pattern data is written over the video signal corresponding to the position at which display is required. Whether the output read from the memory is a video signal or pattern data is discriminated by a signal discrimination circuit in accordance with the read address. Pattern data and the video signal are individually signal-processed. In accordance with a result of the discrimination performed by the signal discrimination circuit, the output from a pattern data processor and the output from a video signal processor are switched and displayed by a monitor.