brightness & contrast

David Tremmel david.tremmel at
Mon Jul 29 14:23:00 EDT 2002

I played around with this a bit (before Ken came out with his excellent
tutorial), but never looked for formal algorithms because I found that
manipulations took so long for my 640 x 480 images (at least on my old G4
400 Mac running OS X).

However, I did come up with a way to mimic brightness adjustment using the
blendLevel command.  I set up a horizontal scrollbar to control the
brightness level; in this case the start and end points are 0 and 200. I
also placed a graphic (BackRect in the example) the same size and location
as the image in a layer behind the image.  Using 100 (the midpoint of the
scroll) as the breakpoint between lightening and darkening, I used the
following script in the scrollbar:

on scrollbardrag
  get round(the thumbPosition of me,0)
  if it < 100 then
    set the backColor of graphic "BackRect" to black
        # This sets the background black for darkening
    get 100 - it
    set the backColor of graphic "BackRect" to white
        # This sets the background white for lightening
    get it - 100
  end if
  set the blendLevel of image "TestImage" to it
end scrollbardrag

This works pretty well, and the results are seen in real time.

Dave Tremmel

> With ColorIt on the Mac I can adjust Brightness & Contrast of images.
> Is there any way I can do either or both of these with Rev?
> atb
> sims
> --__--__--

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