[argyllcms] Re: Profile input white not mapping to output white
- From: Iliah Borg <ib@xxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 26 Nov 2012 12:21:26 -0500
Dear Gerhard,
> one of the problems with applying the profile after white-balancing is of
> course that the profile is not applied to the full raw RGB cube
I guess it is better to take into account how CFA is designed and what are the
intended mechanisms to deal with raw data. One of the things is - it is RG1G2B,
and even if G1 filter has the same colour as G2 they still are often rotated
slightly differently to minimize optical cross-talk and thus have different
efficiency. Sometimes we deal with non-RGB CFAs; and multi-spectrum sensors are
coming too (5 to 7 different types of filters in CFA).
The "body" of the capture for RGGB-type Bayer is asymmetrical for a normal
un-filtered exposure. In overwhelming majority of cases spectral transmissions
of R, G, and B channels are not independent and overlap, and what looks like an
RGB cube is not RGB (hard to call yellow green) and not a perceptual cube.
Making 4 or 3 exposures for each channel to reach "to the right" condition and
recombining to get rid of white balance results in essentially the same profile
as from one exposure normalized for a green channel to nearly reach the
saturation point and with white balance applied (only the dispersion is less
with recombination).
--
Iliah Borg
ib@xxxxxxxxxxx
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