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Controlling the combining of video signals

  • US 5,046,165 A
  • Filed: 01/24/1990
  • Issued: 09/03/1991
  • Est. Priority Date: 04/07/1989
  • Status: Expired due to Term
First Claim
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1. Apparatus for controlling the combining of video signals, so as to produce a composite picture in which a first picture represented by a first video signal is inserted into a second picture represented by a second video signal with such composite picture having a plurality of horizontal scanning lines, and each of said scanning lines including a row of pixels, said apparatus comprising:

  • generating means for generating edge data defining respective edges of a polygon which correspond to edges of said first picture;

    line rate microprocessor means responsive to said edge data to generate information for each horizontal scanning line of said composite picture in which the row of pixels corresponding to the respective scanning line is intersected by edges of said first picture, said information representing horizontal locations of first and second start pixels, said first and second start pixels being pixels in which first and second edges, respectively, of said first picture start to intersect said row of pixels corresponding to said respective scanning line;

    gradients of said first and second edges; and

    a start key value for each of said first and second start pixels which is equal to a proportion of said first picture to said composite picture contained in said first and second start pixels, respectively; and

    key value generator means responsive to said information for each horizontal scanning line of said composite picture to generate a respective key value for each successive pixel in the respective row of pixels in which the key values for pixels preceding said first start pixel are zero, said key values for pixels following said first start pixel are incremented by an amount per pixel determined by said gradient of said first edge until the key value reaches a value of unity; and

    said key values for pixels following said second start pixel are decremented by an amount per pixel determined by said gradient of said second edge until the key value reaches zero.

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