OT Anybody got underexposed digital photos?

phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org
Fri Oct 21 00:43:44 UTC 2005



Back when photography was done with film, selectively correcting
under/over exposure used to be done by 'dodging'. At the print stage, the
negative is projected onto print paper using an enlarger. The photographer
would put various objects in the beam of the projector to reduce the
exposure in the area that had been over-exposed on the negative.

Or you could block the areas that were exposed properly and run the
exposure longer to give the under-exposed areas some extra light.

If you were building a graphical user interface to this operation, you
could have a paddle or wand that you would wave in the area that was
over-exposed. I suspect there are lasso tools in gimp etc that do similar
things.

Peter

>   Or even more of a nightmare, digital photos where one section is
> properly exposed, and the rest is underexposed?  I mentioned recently
> that I was using FreeBasic for a pet project.  That pet project was to
> try and salvage underexposed digital photos.  Like most consumer
> cameras, my Panasonic FZ5 is a great daylight camera, but has major
> problems in low-light situations.
>
>   ImageMagick is an Open Source set of commandline image manipulation
> utilities.  One of the things it can do is convert an image to a text
> file with one line describing each pixel.  A 5 megapixel image comes out
> to approx 150 megabytes but, hey, disc space is cheap.  It can also
> convert the other way.  What I did was to write and compile a FreeBasic
> program that reads the text file representing an image, does some number
> crunching, and outputs a modified text file representing an enhanced
> image.  The modified text file is then converted to an image by
> ImageMagick.
>
>   The process is clumsy, and should really be done using graphics
> libraries, but I'm not that good a programmer.  I like structured
> programming, but my version of "OOPS programming" involves hitting the
> {DEL} key at the wrong time.  Structured FORTRAN and BASIC are just
> right for my abilities.
>
>   Anyhow, I like what I see from my program, and I'll probably post on
> ImageMagick (mailing list) and Gimp (usenet group) to see if anyone can
> implement the algorithms directly.  I'd like to try other people's
> underexposed (or partially underexposed photos) and hear their reactions.
> Preferably via some form of file transfer, as my current inbox limit is
> 10 megs, and I subscribe to a few lists.  I never thought I'd need it,
> but if someone has a GMail invite to spare, this would be the time.  I
> find that bzip2 does much better compression than zip on TIF files.
>
> --
> Walter Dnes <waltdnes-SLHPyeZ9y/tg9hUCZPvPmw at public.gmane.org>
> An infinite number of monkeys pounding away on keyboards will
> eventually produce a report showing that Windows is more secure,
> and has a lower TCO, than linux.
> --
> The Toronto Linux Users Group.      Meetings: http://tlug.ss.org
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-- 
Peter Hiscocks
Professor Emeritus,
Electrical and Computer Engineering,
Ryerson University
416-465-3006
www.ee.ryerson.ca/~phiscock

--
The Toronto Linux Users Group.      Meetings: http://tlug.ss.org
TLUG requests: Linux topics, No HTML, wrap text below 80 columns
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