[argyllcms] Re: Metameric Mismatch
- From: "Brad Funkhouser" <brad.funkhouser@xxxxxxxxxxx>
- To: <argyllcms@xxxxxxxxxxxxx>
- Date: Sat, 11 Oct 2014 09:01:42 -0500
I'm not really talking about the metamerism issue of matching prints to an
original when displayed under different illuminants, though that's a whole
other interesting problem as you point out.
> Ben said: "If your profiling process is good, prints will match when
compared in the same light as you photographed the original." <===
Actually, they'll match under D50, right? They'd only match under the same
light you photographed them if you explicitly define your illuminant in the
profile rather than the standard D50, correct?
And I'm not really thinking about fluorescent, iridescent or metallic issues
in this case.
What I'm grappling with is determining whether there's a way to pre-compute
the metameric defects caused by camera's spectral response curves in
conjunction with my lighting and profiling targets on colors coming into D50
Lab.
In a dream I have 72 equal wattage lasers spaced every 5nm (380 to 730) from
which Argyll can compute my camera's spectral response curves.
Then Argyll can to take existing D50 spectral art color data (say from
spectrashop), transform it using the measured spectral illuminant data for
my actual lighting, and feed it through the computed camera's response
curves to get predicted RGB values.
From there I can send the RGB values through the inkjet target generated
camera profile to get D50 Lab values for comparison with the known D50 Lab
values of the art colors.
This would show me how well my inkjet targets serve as a proxy for any set
of art colors for which there is available spectral data.
So, is there any realistic way to approximate my camera's spectral response
curves? Can some fancy color science math utility take RGB values for a
measured ptfe white patch shot under 4 or 5 significantly different measured
illuminants and somehow glean a close approximation? If this is possible,
is there a utility to feed D50 spectral color data through an illuminant
then through a set of response curves to get expected RGB values?
Thanks.
- Brad
-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-bounce@xxxxxxxxxxxxx]
On Behalf Of Ben Goren
Sent: Friday, October 10, 2014 4:27 PM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Metameric Mismatch
On Oct 10, 2014, at 12:25 PM, Brad Funkhouser <brad.funkhouser@xxxxxxxxxxx>
wrote:
> Seems like there should be some
> significant metameric failure in that instance.
Well, the problem is that it's all illuminant-dependent. If your profiling
process is good, prints will match when compared in the same light as you
photographed the original, but could potentially be radically different when
viewed under various other illuminants.
If the object you're photographing has any metameric tendencies, or has any
sort of fluorescent or iridescent or metallic or other color-shifting
properties, you're not going to be able to reproduce it save by duplicating
the material itself or restricting viewing conditions to the same as when
you photographed it.
(There're some sophisticated multi-spectral techniques that could be applied
to create prints that matched arbitrary illuminants, but it would again be
one print per illuminant...and that sort of thing is, not to put too fine a
point on it, way out of your league and mine as well.)
Fortunately, most artists don't work with those sorts of materials, and the
ones who do understand the limitation; if they're looking for copy work,
it's either for something "good enough" or as a base upon which they'll
hand-apply the special materials.
That leaves you with traditional artist pigments, which tend to be
reasonably stable, such that you generally only have to get a decent shot
under standard photographic lighting equipment with a good profile. You
<i>can</i> get a not-miserable profile out of an inkjet-only print, but
you'll do much better if you add in a bunch of other pigments as well.
Cheers,
b&
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