Re: MonacoPROFILER and UV
Re: MonacoPROFILER and UV
- Subject: Re: MonacoPROFILER and UV
- From: Robin Myers <email@hidden>
- Date: Fri, 8 Sep 2006 19:29:21 -0700
On Sep 8, 2006, at 3:56 PM, Marco Ugolini wrote:
I am not a scientist, so what I am going to say here is pure
conjecture
based on inductive reasoning (or is it deductive...?).
But here it goes: a UV filter is a physical object of a given
shape, color
and texture, made to fit a given condition created by FWAs
(Fluorescent
Whitening Agents). So, if the conditions change (a type of FWAs with
different visual characteristics), it would seem to follow that the
type of
filter would have to change too.
(How am I doing so far...?)
Not completely correct. The UV "blocking" filter (it is important to
note that it "blocks" the UV component of the light as opposed to a
UV filter that transmits UV light) is a pale yellow filter that
transmits the visible spectrum and blocks the UV portion of the
spectrum. So it is not designed for a particular light source or a
particular FWA. It blocks ALL the UV light thus inhibiting the UV
induced fluorescence of the FWA. Most FWAs exhibit UV induced
fluorescence, so they all are affected by the UV blocking filter.
So the question is: do FWAs come in just one "flavor"? Meaning: do
they
always produce one and the same given set of effects on the visible
spectrum, or is there a range to how they look and the effects they
have on
the paper to which they are applied?
No, FWAs come in several "flavors", but they all work in a similar
manner as noted above. Their spectral effects differ, but their goal
is the same, to counteract the natural yellow appearance of paper and
make it look bright and white.
The paper manufacturers use FWAs for two main reasons; to make whiter
white papers for marketing reasons and to produce consistency from
batch to batch for a given paper product. This last reason may be a
bit confusing, but each batch of paper has its own particular color.
To make the same paper product, for example Epson Glossy inkjet
paper, it is necessary for each batch to get a different amount of
FWA to make each batch hit the target whiteness for Epson Glossy.
If the answer is that they come in different "flavors," then how
can it be
maintained that *any one* given UV filter does the most appropriate
job
possible in filtering *any* given set of FWAs?
Explained above. The UV blocking filter simply cuts off ALL UV
wavelengths, thus defeating the fluorescence effect.
If FWAs do come in different "flavors," then it would seem logical
that
software corrections have the obvious advantage of being far more
flexible
and adaptable to the specifics of the case at hand.
Software corrections have to assume a particular amount of UV light
in the viewing environment or the colors will not match. Not all the
colors, but the ones where the paper component is most visible, such
as whites and pale colors.
Also, the software has to assume a known amount of UV in the
spectrometer's light source or the software may under or over
compensate for the FWA.
These two items were noted by Mr. Graeme Gill and Dr. Danny Rich in
their papers in the proceedings of the Color Imaging Conference a few
years ago.
Now, just to make your head spin, it turns out that some FWAs are
also excited to some degree by visible light, i.e. longer wavelengths
than 400 nm. UV blocking filters that cut off all light shorter than
400 nm will not block this visible light excitance. But, the good
news is that this effect with most FWAs is extremely small, so it can
usually be ignored.
The BIG problem with FWAs is that the amount of UV is usually never
known; either in the measurement or in the viewing environments. This
make UV compensation in color management an extremely difficult to
solve issue. At the moment, there are only two packages that offer
software UV compensation; ProfileMaker and possibly Graeme Gill's
Argyle. I do not know for sure about the latter, but it makes sense
because he published a paper on software UV compensation a few years
ago.
The absolute best thing to do with FWA papers is to say NO! Refuse to
buy them, refuse to recommend them, make certain to buy the non-FWA
papers so the manufacturers will quit this nonsense. It is the only
way to have controlled measurement and viewing environments where the
images have a good chance of matching.
Or, the user must relax their requirements for matching to allow for
variance in the images due to uncontrolled UV.
Or, a standards committee must decide exactly how much UV must be in
the measurement and how much must be in the viewing.
One last note, for all of you that are engaged in fine art printing,
FWAs lose their ability to fluoresce after a few years with a
subsequent yellowing of the paper and undoing all your initial color
management work compensating for the FWA. Using inks that will not
fade for decades or hundreds of years is for nought if the paper is
not equal to the task.
Mr. Henry Wilhelm has good information on FWAs in his book "The
Permanence and Care of Color Photographs: Traditional and Digital
Color Prints, Color Negatives, Slides, and Motion Pictures".
Robin Myers
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