While reading the cropping thread, which has varied into general
image-manipulation software (such as IrfanView and FastStone), it has
occurred to me that there is something that is increasingly needed: a
slider for restoring faded colour photographic material. Let's say
mainly prints, as they're likely to be the commonest material that's
going to need it. (Films also.)

I'm sure IV, FS, PhotoShop, PSP, and the others _can_ all be used to
restore the degradation that colour material undergoes, but it would
require skill and knowledge. The main reason is that the various colour
dyes used in such material tend to fade *at different rates*; the end
condition being, usually, a more or less monochrome image consisting of
mostly the green dye, which is probably non-recoverable, but there can
be intermediate stages where some of the other colours are still
present, but in different levels to the green.

What I'm envisaging is a single slider control that would apply the
necessary corrections in their correct and differing proportions as the
slider is varied. (It might have to be a two-dimensional control with
the other axis being just overall brightness and/or contrast.)

I can see _lots_ of difficulties: the biggest probably being either:
different overall casts (colour, brightness, contrast) being caused by
different scanners, or: different fading characteristics due to
different chemistries involved. But I can't help feeling that _some_
common set of parameters might be usable across the _majority_ of
material: certainly, when I see old colour prints that have faded
(especially where only slightly - you could say "faded" isn't quite the
right description; initially just "colours changed"), there does seem to
be a common track the _majority_ of the material follows as it degrades.

For the different chemistries, different presets (Kodak, Kodachrome,
Agfa, Perutz ...) might be relevant (especially for movie film), but I
envisage that as being the more specialist end of the user base; I think
a large proportion of the material is likely to fall close to the "main
sequence" as astronomers would call it. (Would that be, in effect,
"Kodak and its clones"?)

What does anyone think - is it _possible_ that such a slider could
become a common control in image manipulation software, or is it just
too difficult (too many variables)?
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

No sense being pessimistic. It wouldn't work anyway.
- Penny Mayes, UMRA, 2014-August