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Abstract

A video multiplexing system for superimposition of scalable video data streams upon a background data stream and having a video decoder to extract a first luminance signal, an A/D converter to convert the first luminance signal to digital form, a three-port video memory for storing digitized luminance signal, a D/A converter for receiving the stored digitized luminance signal and converting it to analog form, a mixing or multiplexing means, having one input coupled to the D/A converter output, at least one other luminance signal source as an input and controlling inputs for directing the selection of one of the input luminance signals as an output, and a control means such as a microprocessor for controlling the various components. The write operations to the video memory are synchronized to the incoming luminance signal, and the read operations from the video memory are synchronized to the display device. This video multiplexing architecture provides the ability to open a viewport of arbitrary size at any position within a larger display. Scaling of the digitized luminance signal to fit in a viewport of arbitrary size is achieved by varying the frequency of the A/D converter clocks so as to expand or shrink the resulting image.

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First Claim