Exclusion

-- result := a + b - (a*b SHR 7);
on exclusionBlendMode (image1, image2)
  -- using the source image for the width and height
  -- you can add your own code here to determine how
  -- you want to handle this.
  theWidth = image1.width - 1
  theHeight = image1.height - 1
  theImage = image(theWidth + 1, theHeight + 1, 32)
  theDivisor = 127.0
  -- running through each pixel in theImage
  repeat with x = 0 to theWidth
    repeat with y = 0 to theHeight
      theColour1 = image1.getPixel(point(x,y))
      theColour2 = image2.getPixel(point(x,y))
      theRed = theColour1.red + theColour2.red - ((theColour1.red * theColour2.red) / theDivisor)
      theGreen = theColour1.green + theColour2.green - ((theColour1.green * theColour2.green) / theDivisor)
      theBlue = theColour1.blue + theColour2.blue - ((theColour1.blue * theColour2.blue) / theDivisor)
      theNewColour = color(theRed, theGreen, theBlue)
      theImage.setPixel(point(x, y), theNewColour)
    end repeat
  end repeat
  return theImage
end