[argyllcms] Re: Support for ColorSavvy Mouse 2 spectrophotometer

> --- Ursprüngliche Nachricht ---
> Von: Mikolaj Tutak <mtutak@xxxxxxxx>
> An: argyllcms@xxxxxxxxxxxxx
> Betreff: [argyllcms] Re: Support for ColorSavvy Mouse 2 spectrophotometer
> Datum: Tue, 02 May 2006 11:49:46 +0200

> Hard to answer, but maybe You can add 'profile' switch/option to change 
> WB up/down in Kelvin degree. It is possible?

Hmm, I'm not sure, whether just changing the "white balance" is really what
you want, since it would basically affect ALL colors (including white!), and
one consequence would be, that a "white" color in the source image (e.g.
sRGB [255,255,255]) would no longer map to unprinted paper.

(Or to overcome the latter issue, the profiler would additionally need to
"cheat" a bit and to bend the perceptual gray axis towards paper white at
the "upper end").

> My other findings is that I can change illuminant in spectrophotometer 
> >from D50 (default) to D55/D65/D75/A/C/F2/F7/F11/F12. It's not possible 
> to change it with scanner workflow. BTW changing illuminant from D50 to 
> D55 and remeasure pinted chart makes new profile "warmer" than profile 
> made with D50 illuminant, am I right? So still I can't get "cooler" 
> profile?!

That's actually not the goal of the illuminant setting.

You have probably also noticed, that the same print usually looks different,
if viewed under different light sources (tungsten, daylight, fluorescent
lamp, etc.). If for instance a printed gray ramp appears neutral under one
light source, it may show a noticeable color cast when viewed under a
different light source. This is due to metamerism effects, caused by the
interaction of the different light source spectra with the reflectance
spectra of the print. Basically there is not much one can do to overcome
this problem, you can only optimize the profile for one particular viewing
light source, but for other light sources the colors will still be wrong.
And that's where the illuminant setting of the spectrometer comes in the
play - to optimize the profile for a particular viewing light source
spectrum. If you intend to view your prints generally under e.g. tungsten
light, then select Illuminant A when you make the measurements, and create
the profile from these measurements. Printing with the resulting profile
should now give you correct colors, if you view the print under illuminant
A, but under different viewing light sources, the colors may still be off.

So this is also an important general issue to consider, when you judge the
prints visually. If the profile was made for D50, then you should also judge
the print under a D50 light source, and not under a different one.

Btw, if your .ti3 file contains not just XYZ and/or L*a*b* measurements, but
spectral ones, then you can alternatively select the illuminant with the -i
option of the profile command (i.e. if -i is specified, then "profile"
ignores the XYZ/Lab columns in the .ti3 file and computes them from the
spectral reflectances in the .ti3 file according to the given
illuminant/observer).

Regards,
Gerhard

-- 
Gerhard Fuernkranz
nospam456@xxxxxx

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