[argyllcms] Re: Fluorescence

Gerard,

> yes, in this case the measured spectral radiance factors should be the
> same as you'll observe them in your actual viewing environment.

Ah!! I have to try to confirm this experimentally as this will be an
important starting point for in the development of a "Reflectance model with
fluorescence" as Graeme calls it in his article.

> Regarding your statement "And that I should observe a color match?",
> it's not clear to me, what colors you want to compare, and how.

Well, let us say I have some press sheets that were printed on a fluorescent
paper stock. All I want to do is match those press colors I measured onto my
inkjet printer paper.

> Independent from the fluorescence issue, if you intend to view the print
> under illuminant A, then you also should create the profile for an
> illuminant A spectrum (i.e. "profile -iA -o1931_2 ...") and not for a
> D50 spectrum, 

Right. I need to create the Source profile intended for illuminant A (i.e.
"profile -iA -o1931_2 ...") and not for the regular PCS D50 illuminant.

> which implies that media white is the color of the
> unprinted paper under illuminant A.

Yes. The media white of that press profile will encode the  XYZ of the press
unprinted paper integrated for Illuminant A.
 
> Btw, keep in mind that Argyll records the mediaWhitePointTag in the
> "traditional way", i.e. *not* adapted from the viewing illuminant to
> D50. 

Oh??

> Thus, if you use a printer profile generated with "profile -iA ..."
> for proofing with ICC-absolute intent, you may not get, what you expect,
> if your expectation is an *illuminant relative* reproduction, as the
> term ICC-absolute is interpreted by the ICC.

OK.

> In order to get the ICC
> desired behaviour, you need to patch the mediaWhitePointTag and
> mediaBlackPointTag accordingly in the Argyll generated profile.

Patch? You mean after the profile is generated? I wonder if ProfileMakerPro
does that? I'll have to look.

> On the 
> other hand, you should not use the patched profile in conjunction with
> the gamut mapping modes of icclink, since the conversion to/from
> CIECAM02 requires the "true" absolute XYZ numbers, which can no longer
> be reconstructed from the patched profile. If necessary, keep two
> profiles (unpatched and patched) and use the appropriate one for each
> particular purpose.

I'll have at what icclink does? Do I need to use that to convert from Source
to Destination?

> (To avoid a misunderstanding, this ambiguity only applies, if the
> desired viewing illuminant is different from D50, and if the profile is
> thus created for the desired viewing illuminant.

OK.

> Once V4 profiles (or V2
> profiles with CHAD tag) are supported by Argyll, this should also no
> longer be an issue.)

Why? Are V4 profiles "illuminant independent"? Please excuse my ignorance.

Mfg,

Roger Breton  |  Laval, Canada  |  graxx@xxxxxxxxxxxx
http://pages.infinit.net/graxx

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