[argyllcms] Re: Profile input white not mapping to output white

  • From: Iliah Borg <ib@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 23 Nov 2012 19:43:10 -0500

Dear Ben,

> I need to expose another not-quite stop brighter in-camera, thus (almost) 
> doubling the linear data

That is where RawDigger helps - select the target and make sure that your 
whitest patch is close to saturation in the green channels (watch the red too 
if shooting under incandescent light). When you shoot the target without 
blowing background out it is just simpler. When I shoot (always using dark grey 
as a background to reduce flare and colour reflexes) I make sure white patch is 
completely blown out (blinks on camera LCD) and then decrease the exposure 
until it is not. That is especially important if one is trying to profile from 
gamma 1 data - because that helps to fill the whole dynamic range, without 
stretching or extrapolation. You may still want to try excluding the black trap 
from profile calculation and compare the results.

There is also a sort of two-stage approach possible, to reduce the noise. Make 
a matrix profile, and follow it with Lab-to-Lab correction profile.
Iliah Borg

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