[Tig] Scans from different scanners

Kevin Wheatley kevin.j.wheatley at gmail.com
Mon Nov 24 09:44:34 GMT 2014


On Sun, Nov 23, 2014 at 2:35 PM, Jim Houston via Tig <tig at colorist.org> wrote:
> You could also use one APD transform for all negatives, but it is just an average performance
> of all of the negative stocks (print stocks being quite different). Generally speaking,
> a certain class of film (like Vision3) can use the same APD calibration since they
> were designed to operate with each other — the negs often have the same Printing Density.

for anybody going down this route, you might want to use different
targets for base measurements, else you'll get colour casts in the
scans. In fact even with a per stock calibration you will probably
benefit from specific offsets for base. This will allow you to scan
negatives and place a grey card reasonably close to the ideal and be
approximately neutral. This  was most useful when sending VFX vendors
scans as it means they didn't immediately reject scans for being
coloured :-)

What we did was to determine code values for each of the three records
that represent neutral in the printing density space, for example
'445, 445, 445' from that we would calculate where on the specific
negative stock a typical grey card exposure would be, then determine
an amount above base that this would be, and use that to give RGB
targets for the scanned base. The pragmatic approach is to shoot an
actual gray card and adjust until you get what you want, but if you do
it non-analytically you should use an average of several grey card
shoots.

> But most times the exactness of a per negative class conversion isn’t needed,
> and it is a lot of work, no longer justified by the market.

That is for sure

Kevin



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