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Patent Title: Method and apparatus for overlaying two video signals using an input-lock

Assignee: IBM
Patent Number: US5592236
Issue Date: 01-07-1997
Application Number:
File Date:06-01-1995

Abstract: Disclosed is a method and apparatus for combining first and second video signals to produce a composite video signal for display. First and second video sources generate first and second video signals. A chroma key circuit is included for comparing each pixel of the first video signal with a preselected color and generating logic signals indicating whether or not each pixel matches the preselected color. An input lock map stores each of the logic signals when field data is in a first state and provides the logic signals on an output line thereof when the field data is in a second state. A frame buffer selectively receives (1) a complement of the logic signals when the field data is in the first state and (2) the logic signals when the field data is in the second state. The frame buffer is operative to store the composite video signal which is comprised of (1) a plurality of selected pixels from the first video signal which have corresponding logic signals that indicate they do not match the preselected color and (2) a plurality of selected pixels from the second video signal which have corresponding logic signals that indicate they correspond to pixel locations of the first video signal which matched the preselected color.

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