Negation

-- the true "opposite" of Difference Blend Mode
--result := 255 - abs(255-a-b);
on negationBlendMode (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)
  -- 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 = 255 - abs(255 - theColour1.red - theColour2.red)
      theGreen = 255 - abs(255 - theColour1.green - theColour2.green)
      theBlue = 255 - abs(255 - theColour1.blue - theColour2.blue)
      theNewColour = color(theRed, theGreen, theBlue)
      theImage.setPixel(point(x, y), theNewColour)
    end repeat
  end repeat
  return theImage
end