Re: Minolta 5400 or Coolscan V
- From: Kennedy McEwen <rkm@xxxxxxxxxxxxxxxxxx>
- Date: Sat, 16 Jul 2005 20:55:41 +0100
In article <f97id1dpe1u3u181krkpqfn7ilaorjmc0a@xxxxxxx>, Don <phoney.email@xxxxxxxxx> writes
However, the problem with this approach in general is that it relies on post-processing
As does all applications of gamma corrections to CCD scans.
, while my goal has been to scan raw
So, your stuffed - looking to achieve the impossible. You just can;t do what you are looking for *and* apply a raw scan.
and have this raw scan either reflect what's on the film faithfully
Err... you don't like a faithful reproduction of what's on the film, its too blue (and gets bluer in the shadows, as the characteristic curve shows).
Don, if you haven't got enough elbow room using your technique to extend the linear range of scan to about 20 bits or so then there isn't any hope!without introducing artifacts (preferred option, but virtually impossible), or failing that, at the very least extract maximum dynamic range (without any further corruption of data) so when I do get down to proper post-processing I have enough elbow room.
Seriously, your raw scans ought to have more than enough "elbow room" to implement this as a post scan process without the slightest hint of an artefact. We are only looking at a slope for the red layer that is 3% higher than that of the green or blue in the linear region - and that is the gamma difference that is needed. I suspect that the gamma variation between the channels of your monitor or printer will swamp this - although in the case of the monitor it probably isn't a gamma variation but a mis-set black point.
In the toe region, deep in the shadows, it is a bit more significant, and in the opposite direction, with the red being flatter than the green and blue channels by about 40%, but I suspect that you don't really need to worry too much about that if you get the exposure balance correct for the shadows.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
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