Re: Questions on optical brighteners, uv and fluorescence
Re: Questions on optical brighteners, uv and fluorescence
- Subject: Re: Questions on optical brighteners, uv and fluorescence
- From: Marcelo Copetti <email@hidden>
- Date: Mon, 30 Sep 2002 08:16:45 -0300
Good morning,
I have some questions about papers with witheners.
Can I profile papers with and without whiteners with UV filters?
Can I have distortions with UV filters in papers that has no whitener?
UV filter has the same problem that polarization filter? Lens usually
has color and this can deviate readinds.
Could you explain in details the method that you talked about read deep
blue, UV and compute the whitener stimulation.
Thanks dor all
On segunda-feira, set 30, 2002, at 04:35 Brazil/East, Graeme Gill wrote:
>
neil snape wrote:
>
>
> I'll try to re-phrase although it's rather exploration into areas I
>
> know
>
> nothing about even if it exists.
>
> At some point ink can be covering the surface of the paper in a way
>
> that can
>
> be cumulative or subtractive of the uv and fluorescence issues. Could
>
> the
>
> inks then filter the qualities of the uv characteristics of the
>
> paper as
>
> the inks could modify these issues.
>
>
OK, assuming that you're not talking about spatial effects (ie. not
>
talking about edges of dots etc.), then I think in general it's right
>
to assume that yes, inks will have a filtering effect on the deep blue
>
and UV wavelengths, the very wavelengths that are absorbed by the
>
whitener
>
and re-emitted at longer wavelengths (visible blue).
>
>
This translates to meaning that the effect of an ink on a paper
>
with fluorescent whiteners, is not simply modelled by multiplying
>
the spectral absorbency of the ink by the spectral reflectance of
>
the paper.
>
>
The model I use for compensating for Fluorescent Whitener effects
>
in profiling certainly takes the view that I need to measure the
>
absorbency of the ink in the deep blue and UV, to compute how
>
much stimulation the whitener is getting, and then filter the
>
resulting re-emitted light by the ink absorbency at the
>
emission wavelengths. This relatively simple model had a
>
very pleasing agreement with reality, in the verification checks
>
I've made.
>
>
> Could applying absolute colorimetry be
>
> used in a significant way to modify the behaviour of the base paper
>
> to mask
>
> uv brighteners?
>
> For example uv doesn't pass through glass well at all. Does uv pass
>
> through
>
> the inksets we use or which colors?
>
>
I don't see that "masking" the effects of brighteners is at all
>
desirable. The brighteners are active and present in the real world.
>
Measuring and modelling the effect of ink on paper as if they weren't
>
there, isn't going to get results that are useful in the real world
>
(if this is what you meant by "masking").
>
The best we can do is more accurately measure and model the effects
>
of brightners, and compensate for the different measurement
>
conditions that exist between an instrument, and a viewer in the
>
real world.
>
>
The measurement instruments that are fitted with UV blocking
>
filters, do seem to suppress the action of the fluorescent paper
>
whiteners, and therefore measure color in an even more unrealistic
>
way compared to a human viewer. This also means that it's then not
>
possible to estimate the quantity of whitener in a paper by examining
>
the spectral readings from such an instrument.
>
>
Graeme Gill.
>
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[demime 0.98b removed an attachment of type image/jpeg which had a name of Logo Image Pixel web.jpg]
Marcelo Copetti
Image Sistemas/Pixel Systems
Gerente de Suporte/Support Manager
Rua Francisco Nunes, 1739/ 1739 Francisco Nunes st
Curitiba - PR - Brasil
CEP/ZIP: 80215-000
Tel(Phone): 55 41 333-7778 ext 43
Fax: 55 41 333-5222
Celular (Cell): 55 41 9968-3032
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