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Abstract

A method and system for combining digital data signals representing digitized images to implement a DSK operation in one mixing stage. The system requires only one mixing circuit, rather than two as in conventional DSK systems. In preferred embodiments, the DSK operation processes an input video signal having pixels a.sub.k, an input video signal having pixels b.sub.k, a stream of single-color pixels B, and a fade control signal .beta., to generate a stream of output pixels u.sub.k =(1-.beta.)v.sub.k +.beta.B, where v.sub.k =(1-.alpha.)a.sub.k +(.alpha.)b.sub.k, and .alpha. is a key signal which can have a different value for each pixel a.sub.k. The value of .alpha. can be constant for an entire frame of input pixels a.sub.k or can have a different value for each individual pixel a.sub.k. Typically, the value of .beta. is constant for each frame of input pixels a.sub.k. Preferred embodiments of the system employ a single mixing circuit, which receives five input data streams: first pixels a.sub.k, second pixels b.sub.k, a third stream of scaled pixels .beta.B, first key signal c.sub.v =(1-.beta.)-.alpha.(1-.beta.), and second key signal c.sub.g =.alpha.(1-.beta.). Preferably, the system includes a look-up table which outputs one value of the second key signal c.sub.g in response to each input pixel b.sub.k, or in response to each pixel of an external key video signal, and the system includes simple circuitry for processing each value of the second key signal c.sub.g to generate a corresponding value of the first key signal c.sub.v.

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