[argyllcms] Re: Digital Camera Profiling from ColorChecker 24
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 20 Jan 2021 11:10:52 +1100
graxx@xxxxxxxxxxxx wrote:
“Profile check complete, peak err = 8.409639, avg err = 2.301651“
Hi Roger,
note that this is a "self fit" error. Many things have an influence
on this error in regard to a linear input sensor, not least being the fact
that the sensors spectral sensitivities are probably not the same
as the standard observer. This means that there can probably not be a perfect
fit between the sensor RGB values and the XYZ observer values, even
if all other effects (i.e. flare, flat fielding, sensor linearity and
zero etc.) are removed.
Iliah Borg wrote:
As to how Argyll processes a non-linear TIFF to produce a matrix profile with
gamma 1, Graeme
is the authority; I simply put a question here hoping he could answer.
Depending on the
internal workflow in a converter, you may not even want the gamma 1 profile.
It's just a fit to the data. Of course you want more data points that free
variables
if it is to mean anything, particularly if the data points have random
measurement
errors. Things like flare can unduly affect gamma estimation if the dark data
points
end up with sufficient weight. From the gamma number produced, it appears that
this is not
a linear RGB output that Roger is using for the profile.
Cheers,
Graeme Gill.
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