> The images I edit are usually around the 3500x2800
> or so mark at 30 bits
> depth.  I've recently tried Gimp on such images and
> have found it to be
> lacking to put it mildly.

thats odd. that size should be fine. i work in film
res all the time (4kx3k) at 32bpp (yes, i know film
should be done at 48 or 64 bpp to prevent banding, i
only work this res for testing)
> It wouldn't even load 30-bit TIFF files, I had to
> truncate them to 24-bit,
> so losing three quarters of the range of each colour
> component, not much
> of a problem until you start messing around with
> levels, contrast, and
> other such things --- 1024 levels gives me much more
> headroom than 256!

yes, though using curves can sometimes lose less color

> Being as the scanner already loses masses of
> dynamics from a scanned
> processes so it's not a
> problem with RAM.

look at your prefernces, whats your tile cache set to?
> Preview mode in other similar operations (e.g. gamma
> curve changes) is
> preview, but not the
> 10 minutes or so that gimp takes.
> I'm trying to find out what's going on here, am I
> doing something wrong,
> or is there a fundamental performance problem with
> the levels tool and
> other such tools? If there is, does anyone know of
> any alternative
> programs that can preview contrast, gamma changes
> and levels changes on
> large images in near-realtime?

your monitor is as real time as it gets. i wrote a
little utility for gamma correction,
but it only works with certain X servers (hopefully
later releases of XFree86-4 will fix the situation)

other than that, the gimp should have no problem with
this. you could also try xv or ee (electric eyes)
> Please don't unhelpfully suggest as someone else in
> a newsgroup did, that
> I break out emacs and start to code, I'm no coder,
> I'm a photographer, and
> not very good at that either ;-)

c is not as difficult as it looks. if youve never
programmed before and it scares you, try python, which
you can script the gimp with. 
> Thanks for your time.

anyway, for what your doing, your better off with
photoshop monitor calibration is better in windows and
mac (way better in mac), and photoshop can deal with
16bit images, and a better set of color correction
toys. the fact that photoshop uses LAB colors
internally helps.

another alternative is to try http://film.gimp.org

gimp 2 will support deeper color depths and have
better support for converting between color spaces. i
think well quickly have better color correction tools
to with all that.

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