# Re: Adjusting contrast and brightness

William L. Sebok (wls@astro.umd.edu)
Thu, 3 Dec 1998 12:05:08 -0500 (EST)

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I said:
> Actually, automatically choosing brightness, contrast and gamma from
> a selection on the preview is exactly the feature on the windows
> driver for my Umax S12 that I miss most in sane. That and being
> able to zoom the preview window to make a decently precise
> selection.

David Fox:
> Having the software actually select the contrast and brightness and
> gamma is a lot trickier, with subjective elements. Its one of those
> problems, like the travelling salesman problem, that are impossible in
> theory but solved in practice every day. Are the algorithms for doing
> this proprietary, or are there no image processing experts here? I
> know about image synthesis, but not much about image processing.

One of the things the Umax S12 software sets automatically is the dark and
brightest pixels. This is fairly easy to measure and is usually what I want
to do anyway (of course how it maps into the backend controls is another
matter). It does indeed show the effect of the adjustments on the preview
without rescanning. However I don't really think it gets it right, showing
the preview as lighter than the the scanned image looks. I suspect the problem
is a disagreement with photoshop and the gimp over monitor gamma.

Oliver Rauch <oliver.rauch@Wolfsburg.DE> said:
> Will all be included into my new frontend.
> Online gamma/contrast/brightness-changes already work,
> automatic contrast/brightness is easy to implement.

> I think I will make a pre-alpha-version available next week!

Great! Is zooming of the preview window present in this alpha version?
I would love to alpha test it as lack of these features has kept me preferring
to keep using the windows software.

Bill Sebok Computer Software Manager, Univ. of Maryland, Astronomy
Internet: wls@astro.umd.edu URL: http://www.astro.umd.edu/~wls/

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- Next message: David Fox: "Re: Adjusting contrast and brightness"
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- Maybe in reply to: David Fox: "Adjusting contrast and brightness"
- Next in thread: Matthias Fleischer: "Re: Adjusting contrast and brightness"
- Next in thread: Jon Knight: "Re: Genius scanners"