Re: ISO 12647-3 measurement (IT8.74 or ECI 2002) Lab data list---black backing and white backing
Re: ISO 12647-3 measurement (IT8.74 or ECI 2002) Lab data list---black backing and white backing
- Subject: Re: ISO 12647-3 measurement (IT8.74 or ECI 2002) Lab data list---black backing and white backing
- From: Roger Breton <email@hidden>
- Date: Wed, 12 Jul 2006 23:11:49 -0400
> I have seen 3 definitions in ISO standards for backing: white, black, and
> multiple sheets of the same paper stock. If the paper stock is identical
> between two systems you are trying to match, there should be no problem
> using any of the above. If you are doing absolute rendering for proofing on
> different paper stocks or performing virtual proofing on a display, then you
> will observe significant differences of appearance, particularly between
> very thin and very thick paper stocks.
How, then, could you compare thin paper stocks among themselves, on color?
If measured on a black backing, they could appear (some #5 coated grades I
know) very neutral, with a* and b* close to zero. On the other hand, if
measured on a white backing, like the Spectroscan table, the same paper
shows a negative b* value, typically around -3, again for some papers I'm
familiar with. As a consequence, I can hardly tell unequivocally what is the
"color" of a thin paper stock. Lately, before loosing my mental sanity, I
started measuring over "nothing": I place the paper one inch away off the
surface of my desk so there is no backing behind it, just the space between
the top of my desk and the floor, about 30" or so. Then I measure, with my
SpectroEye, holding the paper from underneath between my fingers. It works.
But it's not an ISO standard :(
> In our work with Matchprint Virtual, we have confirmed that the best result
> occurs when a neutral gray backing is used such as Munsel N7 or N8.
You don't mean to use an N8 backing to measure paper?
> This is
> actually pretty logical -- N7 or N8 is about a 50% neutral reflector and is
> the color of every light booth I have ever seen -- never seen a light booth
> that is black or white!
Well, I once stumble upon a light cabinet maker, in France, (I can dig out
their URL if you're interested) that offered a complete of black viewing
booths. Isn't the internet "eye-opening"?
> Regards,
> Dr. Christopher J. Edge
Regards,
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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