Imaging lingo utility
Imaging utility

  Imaging lingo utility
From: "James Newton" <>
To: <>
Subject: Re: <lingo-l> Imaging lingo utility

> I've written a utility that will import the screen grabs, compare
> them against a key image, and crop each so that only the changed
> pixels remain.  Now I'm looking to optimize it.

Hi Kurt,

Thanks to Macromedia's Werner Sharp, here is a handler that will
calculate the difference between two images.  It takes roughly 
750 ms to treat an 800x600 pixel image on a Pentium II at 400 MHz.

Hats off to Werner!



on isolateDifferences(image1, image2) --------------------------------
  -- Returns an image which represents the differences between
  -- <image1> and <image2>.
  -- PARAMETERS: <image1> and <image2> are expected to be images of
  -- identical size, shape and color depth
  -- This handler was generously sponsored by Werner Sharp.
  -- Determine dimensions
  imageRect = image1.rect
  -- 1. create copy of image1
  delta = image1.duplicate()
  -- 2. isolate different pixels as non-white
  delta.copyPixels(image2, imageRect, imageRect, [#ink: #reverse])
  -- 3. create 1-bit mask image and fill with solid black
  theMask = image(imageRect.width, imageRect.height, 1)
  theMask.fill(imageRect, rgb(0, 0, 0))
  -- 4. copy only non-white pixels over to destination but at the
  --    same time make them white so we're left with only white and
  --    black pixels.  The white ones are the different pixels, the
  --    black pixels are the same.
  options = [ \
#ink:       #backgroundTransparent, \
#color:     rgb(255, 255, 255), \
#bgcolor:   rgb(255, 255, 255) \
  theMask.copypixels(delta, imageRect, imageRect, options)
  -- 5. invert the 1-bit mask
  theMask.copypixels(theMask, imageRect, imageRect, [#ink: #notCopy])
  -- 6. use theMask to copy only the different pixels over from image2
  delta.fill(imageRect, rgb(255, 255, 255)) -- recyle delta
  delta.copyPixels(image2, imageRect, imageRect, [#maskImage:theMask])
  return delta
end isolateDifferences

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