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Abstract

A chroma key generation method and apparatus are provided (for both composite and component video) in which an operator selects a reference portion of a color television image to identify it as the background of the image, and a strobe signal is then generated whenever the video data that is presently passing through the keyer is within the reference portion of the color video image. This strobe causes the video data corresponding to that portion of the image to be stored. A microprocessor then determines attributes of the video in the reference portion of the color image from the stored video data, these attributes including a reference hue, .alpha.. The image hue .THETA. at each pixel in the color image is correlated with the reference hue .alpha. to produce a correlation signal that has a first range of values for points of the color image at which the image hue matches the reference hue and a second range of values for points of the color image at which the image hue does not match the reference hue. After further processing, this correlation signal becomes a chroma key signal. The attributes of the video in the reference portion of the image are employed via the microprocessor to process the video signal and associated chroma key signal in several ways, including background suppression matte generation, shadow clip level input to the shadow comparison circuitry and the gain of the key signal variable gain comparator.

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First Claim