Re: RelCol Mapping of Middle Gray
Re: RelCol Mapping of Middle Gray
- Subject: Re: RelCol Mapping of Middle Gray
- From: Ray Maxwell <email@hidden>
- Date: Tue, 08 Mar 2005 09:26:43 -0800
Steve Upton wrote:
I'm not an authority but doesn't reflective density depend on paper
white and 100% solid? It would seem like that value would vary as well
In Lab, 50,0,0 IS middle gray by definition. So this is one of the values that would NOT change.
Hi Steve,
Instruments that measure density (densitometers and spectrophotometers)
can be set to measure density "relative to paper" or "absolute".
Densities specified in the SWOP standards are "absolute", Status T,
paper dry, and non polarized. Slowly SWOP is moving from density to
colormetric readings (TR001).
A few other instrument and measurement tidbits:
Spectrophotometers are much more accurate in measuring density than
densitometers. Filter's and light sources' spectral characteristics can
vary and the calibration procedures most manufactures recommend for
densitometers do not correct properly for these variations.
Spectrophotometers on the other hand can normalize out these variations
by using the white calibration technique.
Effective dot area measurements are made relative to paper white and
Maximum density of the solid. Warning, the filter Status has an effect
on these readings. This means that you do not get the same readings if
you change from Status T to Status I. This again is due to spectral
characteristics.
Now I have a question.
I know that reflective Lab readings are absolute measurements. However,
what is the reference when making emissive readings?
Thanks,
Ray Maxwell
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