On Mon, 11 Jun 2001 18:45:13 -0400 Dave King (email@example.com)
> Sorry Tony, but I don't agree with this. Neg films vary primarily in
> the mask layer.
But that seems to be a variable, since mask density appears to vary
according to processing.
> Processing is standardized by manufacturers, and good
> labs use the same technology to insure consistency with C-41 as they
> do with E-6. In my experience, neg film of one type is as consistent
> as chrome film. If you shoot under controlled conditions in the
> studio and use a good lab for processing, you'll see this when you get
> to the darkroom. Exposure is another story, but the manufacturer or
> lab can't be faulted for that. But even here color negs vary less
> than chrome films.
It's true I don't see a lot of variation in C41 films of the same type,
but it's not the film which varies, it's the image. The scanning task is
quite different from scanning slide. With slide, you have a fixed
reference, with neg it's interpretive.
The source of difficulty here is the latitude of C41 and ability to
produce uncorrected results across a wide range of colour temperature and
exposure which you sort out later. With slide, you have next to no
tolerance. If it's screwed on the film, you aren't going to be able to do
a great deal with the scan as the wide OD range occupies all, or nearly
all, of the dynamic range of the scan.
If you always shoot colneg under more or less controlled conditions, and
place exposure on the same part of the curve (conditions more or less
imposed by slide) then, yes, I would believe profiling could be done with
reasonable precision - given a consistent lab.
But the utility of colneg is the amazing ~10stop range, which enables
exposure to be located however you want on the curve, and allows enormous
liberties to be taken with illuminant colour, including mixed sources.
In this scenario, the colneg is only a waypoint on route to the final
image which exists nowhere except in your head. You absolutely don't want
a mechanical, invariant translation as you would with slide+profiles. It
will look horrible, say, to get a 'straight' scan of an image taken under
flourescent without filtration.
You have a lot of freedom to muck about with values, as most images leave
plenty of headroom once scanned.
DH's suggestion of a ring-around of profiles seems like it maybe a handy
shortcut from the info locked up in the neg to an image which approximates
what you were after, at least part of the way - by mapping response for
film under a variety of conditions.
To restate St Ansel for the C21st 'The negative is the score, the print is
the performance, and profiles are pianola rolls' :)
I'm sure you know all this stuff anyhow, and do it anyhow ('I am the
colour management' :-) All I'd add is : isn't it curious how much colour
correction can vary from one neg to the next, even when taken in the same
place and same time.
http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner
info & comparisons