| abstract |
A picture overlay system assures proper size and placement of picture overlays in simultaneous picture displays. The system comprises a video memory (350, 356, 358) and a control circuit (300) for writing and reading information from a video signal into and out of the video memory, the information relating to video data and field type. A reading circuit (680) supplies information from the video memory synchronously with a display for another video signal. An interpolator (337) selectively compresses and expands the information read from the reading circuit. The field type information undergoes the compression and expansion together with the video information. A decoding circuit (310) decodes the field type information to identify first and second types of fields and an absence of valid video data. A multiplexer (312) combines the video signals for simultaneous display, operating responsive to the decoding circuit. The reading circuit can comprise an asynchronous line memory for the information read from the video memory, having a write port operable synchronously with the reading of the video memory and a read port operable synchronously with the display for the other video signal. |