RE: Correlating Tappi Brightness
RE: Correlating Tappi Brightness
- Subject: RE: Correlating Tappi Brightness
- From: Roger <email@hidden>
- Date: Wed, 05 Aug 2009 14:13:45 -0400
Mike,
I was under the impression that those instruments built from the group up
for Tappi Brightness testing, such as the Zeiss ElRepho, had a physical
light source that closely mimics illuminant C.
(not long ago, one such sold for $150 on eBay -- couldn't believe my eyes)
My 530 also offers a function to approximate Tappi Brightness. I once spoke
to X-Rite about it and all they do is to report reflectance at 452nm. Better
than nothing.
Roger
> -----Message d'origine-----
> De : Mike Eddington [mailto:email@hidden]
> Envoyé : 5 août 2009 12:55
> À : Roger
> Cc : ColorSync
> Objet : RE: Correlating Tappi Brightness
>
>
> >>Tappi uses an illuminant C type of light source,
> >>unlike the tungsten light source used in an EyeOnePro, for instance.
>
> I believe that the illuminant "C" is mathematically equated from the
> tungsten illuminant of the measurement device, rather than a true "C"
> illuminant in the measurement device. At least that's how it has to be
> for our Xrite 938 that measures Tappi brightness. Yes, there would
> definitely be a discrepency correlating brightness using illuminant C
> to
> D50 CIELab, which is why I indicated that the measurement device (0/45)
> and illuminant would ideally be he same.
>
> >>Personally, I never tried to relate the two measurements
> >>mathematically, in Excel, for instance. I live with 72
> >>Brightness corresponding to L89 for
> >>SWOP5 and 88 Brightness corresponding to L92 SWOP3. I know,
> >>far from perfect.
>
> I think brightness on the whole is far from perfect myself. I'm not
> really sure why one would even want to correlate brightness to L*a*b*,
> jut wondered if it were mathematically possible.
>
> Thanks Roger,
>
> Mike
>
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