Re: was: Brightener in Epson Premium Glossy
Re: was: Brightener in Epson Premium Glossy
- Subject: Re: was: Brightener in Epson Premium Glossy
- From: Graeme Gill <email@hidden>
- Date: Thu, 03 Oct 2002 15:19:13 +1000
Roger Breton wrote:
>
As a matter of fact, a SpectroCam operated in "Spectral Camera" mode behaves
>
like a Spectroradiometer!
I found that to use it this way successfully, you had to read the
fine print, and use a white reflective surface to bounce the
illuminant into the spectrocam. White polystyrene foam worked
the best (it has a flatter response in the short wavelengths
than paper). Note that the spectrocam software lets you calibrate
the effects of the reflector out of the readings.
>
And, for my money, I believe it is the best prescription for measuring
>
fluorescent papers as the Xenon light source excites more of the UV than an
>
incandescent light source. This will yield, in my experience, measurements
>
that are more closely related to D50 viewing conditions. Just so that I
>
don't get the napalm, when a substrate has no OB, I don't use a SpectroCam
>
but when it does, well, my experience shows that I get better profiles by
>
using it than any other spectros out there -- x41, DS and EyeOne. Some
>
people report good results with UV filters on their instrument, my
>
experience contradicts this. What can I say?
After a little discussion with Marc Levine, and some though, I think
I may have arrived at a possible reason why some people get improved
results using UV filter instruments, and some might not.
What's important in the instrument is not the amount of UV it puts out
compared to its overall output, but the balance of light at the wavelengths
where the whitener is stimulated (UV) to where the whitener emits (blue).
Without fluorescence, the shape of the instrument illumination spectrum
is irrelevant, because the instrument divides the illumination out of
its readings in computing the reflectance of the sample.
By assuming a stimulation and response spectra for typical
FWA (Fluorescent Whitener Additive), I've concocted an
illuminant "Normalized UV factor" for four light sources
I happen to have the spectra of. What this represents is the
relative energy of the UV wavelengths compared to the energy
at the blue wavelengths. The bigger the number, the more the FWA
will affect the resulting instrument readings, and the
bluer they will appear:
Illuminant NUVF
A 14.3
D65 30.8
D50 fluoro sim 1 3.9
D50 fluoro sim 2 8.5
What this seems to mean is that if you have an instrument
that measures under illuminant A, and you view your profiles
in a simulated fluorescent tube D50 or D65 viewing booth,
the results will look too yellow, because the instrument was
getting more FWA activity than your viewing booth is.
If you switch to an instrument that has a UV filter, then
its NUVF will be much lower, better matching the NUVF that
your viewing booth has.
If you are viewing your results outside, or in a real D50 or
D65 viewing conditions, your results will look too blue, because
you are getting more FWA activity than the instrument was getting.
If you switch to an instrument that uses a real D65 illuminant,
then its NUVF will better match your viewing environment, and
you will get better looking results.
It would be interesting to see if this theory holds water
in other peoples experiences.
Graeme Gill.
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