Video processing circuit for telephone line transmission - uses microprocessor and comparator to determine difference from previous image for transmission of difference signals

摘要

The video signal is applied to a fast A/D converter (1) whose output is sampled in time periods for application to a dynamic RAM (4). The cycle time for the RAM is less than the sampling period. A line and frame sync. separating circuit (3) operates in conjunction with an interface (9) for the memory to ensure that the memory is refreshed and that the sampling clock is controlled. A microprocessor based processing circuit (5) with peripheral units reads the memory registers corresponding to the different areas of an image and determines which have varies more than a predetermined level compared with a previous image. This process is aided by a comparator (7) and an authorisation system (8) which selects and accumulates data for the areas for comparison. The differences only are transmitted through a matching interface for the telephone line.