Re: Spectrophotometer measurements
Re: Spectrophotometer measurements
- Subject: Re: Spectrophotometer measurements
- From: Dan Reid <email@hidden>
- Date: Wed, 10 Jul 2002 12:10:22 -0600
on 7/9/02 8:57 PM, bruce fraser at email@hidden wrote:
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At 5:00 PM -0600 7/9/02, Dan Reid wrote:
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>
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> My understanding is the black table of a SpectroScan was designed to for
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> thin papers like newsprint. If you have the white table instead you
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> definitely need blank sheets OTW your L* will be off. On the flip-side
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> lighter colors and highlights may measure in accurately too because of the
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> black backing. I think the black table is based on an ISO standard, Henrik
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> may have words on this. Have you tried building a profile with a black
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> table?
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>
Standards organizations like to measure over a consistent background
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so that they can compare measurements. The problem is that when you
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measure thin papers over black, you get a lower white point than the
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viewer typically sees (unless the other side of the paper is covered
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with black ink). It's not a huge problem on the output side, but it
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really screws up the device-to-PCS tables and gives you an even
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nastier soft proof than the accurate one would.
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>
Measuring over a stack of blank sheets doesn't let me compare the
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press data with FOGRA or SWOP standards, but it produces a profile
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whose soft-proof is closer to the experience of the viewer than one
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measured over black, without having to do a ton of profile editing.
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>
> Lining up printed sheets together may give you inaccurate measurements since
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> you're measuring through 2 or more thin papers will ink applied. I think the
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> saturation will be off. You should be able to easily *measure* this with the
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> Gretag MeasureTool as you've said.
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>
Saturation and lightness both. It's not a good idea!
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> I always, if given the option, use several sheets of the same paper taped to
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> the SpectroScan table. Best if they can send some blank sheet too instead of
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> kludging it.
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>
Me too, unless I'm trying to compare a press to a published standard
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that was measured over black.
Thanks for the clarification. So if you want to compare Apples to apples for
FOGRA and SWOP conformance then you should measure the sheets with the black
table. Makes sense for sheets printed on both sides.
Do you know if the TR001 recommends measuring sheets with the black table?
--
Dan B. Reid
RENAISSANCE PHOTOGRAPHIC IMAGING
http://www.rpimaging.com | email@hidden
Toll Free: (866) RGB-CMYK
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