Re: On the effect of florescence
Re: On the effect of florescence
- Subject: Re: On the effect of florescence
- From: Robin Myers <email@hidden>
- Date: Tue, 1 Mar 2005 15:38:57 -0800
On 1 Mar, 2005, at 10:19, John Wickham wrote:
On Monday 1, March, 2005, Robin Myers wrote:
I test the printer paper before making any target measurements. If an
FWA is present, I use a UV Cut filtered instrument. Although it is
possible for software to guess that an FWA is present and remove some
of the effects from the measurements, it is also possible for the
software to misdiagnose certain colors (e.g. blue-grays) and apply
correction where none is needed, producing a wrong result. Using a UV
Cut filter removes these ambiguous situations from the measurements,
making the software work better.
Robin, are you saying, if there is no FWA present leaving the UV Cut
filter
on could cause an unreliable reading?
No. Leaving the UV Cut filter on does not adversely effect the printer
target measurements, regardless of any FWA. If there is an FWA present,
the readings are more consistent between paper stocks with the UV Cut
filter on. Using the UV Cut filter also means that the profiling
software does not have to compensate for the FWA.
Paper manufacturers put FWAs in the paper to make their paper appear
whiter and brighter by adding extra energy into the blue area of the
spectrum, which counters the natural yellowness of paper fibers (and
fabrics). FWAs make your clothing "whiter than white", your teeth look
brighter (yes, FWAs are in your toothpaste), but they can be a problem
with prints.
The issue with FWAs is the amount of UV excitation available in the
print viewing environment is usually unknown and uncontrolled. Prints
viewed in illuminations low in UV light will not have the same look as
viewed in conditions with higher UV light. Also when comparing prints
made on different paper stocks, the amount of FWA in each paper will
give each a different appearance. Using the UV Cut filter puts all the
paper measurements to the same reference point.
I do not believe there is any ASTM standard on this since the type and
amount of UV blocking filtration would depend on the instrument's
light
source (e.g. tungsten-halogen, xenon flash tube).
I have been under the assumption that xenon flash, because of it's
color
temperature? did not need a UV Cut filter. Could you comment on this?
Color temperature has no correlation with the amount of UV energy
present in the illumination. Xenon lamps produce spectral power
distributions from the UV to the infrared, so there is more than enough
energy present in a xenon lamp spectrophotometer to excite FWAs. In a
quick search, there were several pages on the Web discussing methods of
UV curing adhesives and other compounds using Xenon lamps, flash and
continuous.
Color temperature is a metric for comparing the color of a light source
to a black body radiator at a specified temperature. So, if the xenon
lamp has a color temperature of 6500 K, then the color appearance
should be similar to a black body radiator at a temperature of 6500 K.
Robin Myers
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden