Re: proper way to convert from linear gamma negatives?

On Tue, 12 Jul 2005 22:32:00 +0100, Kennedy McEwen
<rkm@xxxxxxxxxxxxxxxxxx> wrote:

>>BTW, what do you think of the procedure in general (i.e. comparing a
>>few scans and creating a generic curve out of that - also, see below)?
>>
>If you used a Q60 or IT-8 slide, I would call it a film profile. ;-)

It wouldn't be the first time I "invented" something that has already
invented... ;o)

However, I found the above "image comparison" (whereby I extract a
curve needed to convert from one into the other) very revealing in
many other instances and it's one of my main tools now!

>>How would you "boost" such a curve? Just lift the middle of each
>>channel or change the ratio in some way?
>>
>If you just lift the middle then you will only change the colour balance
>in the middle of the density range. If you want to change the balance
>across the density range then you have to change the overall ratio - and
>you could do that with the analogue gain though.

That's actually why I asked because after all the many (and elaborate)
wild goose chases I always keep getting back to analog gain which is
where I came in 3 (!) years ago... :-(

I found recently that boosting analog gain of a positive scan and then
setting the gray point (hence the "lifting the middle" reference
above) produces much better images than setting the gray point of a
Nikon's "Kodachrome mode" scan!

Upon closer inspection the Nikon's Kodachrome mode graypoint adjusted
scan actually has a moderate red tint! The analog gain corrected and
graypoint adjusted scan, by comparison, is much purer and much truer
to the original.

The catch, however, is jamming the "square peg" of linear analog gain
into the "round hole" of a non-linear characteristic film curve. :-/

Don.
.

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