Overlay

--if a < 128 then
--  result := (a*b) SHR 7
--else
--  result := 255 - ((255-a) * (255-b) SHR 7);
-- ****** this is hard light mode in photoshop ******
on overlayBlendMode (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))
      if  theColour1.red < 128 then
        theRed = theColour1.red * theColour2.red / theDivisor
      else
        theRed = 255 - ((255 - theColour1.red) * (255 - theColour2.red) / theDivisor)
      end if
      if  theColour1.green < 128 then
        theGreen = theColour1.green * theColour2.green / theDivisor
      else
        theGreen = 255 - ((255 - theColour1.green) * (255 - theColour2.green) / theDivisor)
      end if
      if  theColour1.blue < 128 then
        theBlue = theColour1.blue * theColour2.blue / theDivisor
      else
        theBlue = 255 - ((255 - theColour1.blue) * (255 - theColour2.blue) / theDivisor)
      end if
      theNewColour = color(theRed, theGreen, theBlue)
      theImage.setPixel(point(x, y), theNewColour)
    end repeat
  end repeat
  return theImage
end