Re: UV Filter
Re: UV Filter
- Subject: Re: UV Filter
- From: email@hidden
- Date: Thu, 11 Oct 2001 17:13:41 +0100
On Thu, 11 Oct 2001, Robin Myers wrote:
>
If you are only measuring paper output for ICC profiling, leaving the UV
>
blocking filter on the Spectrolino will not hurt anything. The only situation
>
you may want to watch out for is one where the paper is glossy and without a
>
brightener, then you may want to switch to the polarizing filter.
>
Since glossy materials reflect approximately 4% of the illuminant back to the
>
sensor for a 45/0 degree geometry (i.e. Spectrolino and many other devices),
>
the polarizing filter reduces this 4% significantly, letting the
>
spectrophotometer make more accurate readings of the color.
My experience with the Spectrolino and its Pol filter led me to believe
that the Pol filter effectively cuts off UV, too. To find out the influence
of optical brighteners, I usually take measurements with the Spectrolino or
Spectroeye and compare b* with the D65 filter and the U (= No) Filter. But
once I tried also the UV and Pol filter and found only small differences.
At first, I created all profiles with the Pol filter mounted. It seemed
especially necessary for the black ink in the sheet-fed press which "gleamed"
a little even if the paper was matte. Without Pol filter I got L* values
corresponding to a density of 1.2-1.3 instead of around 1.8-2.0 as measured
with Pol filter (and standard densitometer). So I used the Pol filter to
prevent my proofs from looking grayish.
However, Lab measurements are more saturated with the pol filter, even if the
surface has not much gloss. To my eye, proofs appeared ok when using "Pol"
profiles for both proof and press, but mixing Pol and non-Pol was really bad.
When you give Pol press profiles to other people this can be dangerous. There
may exist situations where Pol profiles work, but in general I doubt that Pol
and non-Pol profiles are really compatible.
(And there is this gut feeling that the slightly greenish appearance of the
Pol filter glass somehow disturbs color fidelity - even if the device
compensates
by measuring the white tile: and shouldn't the L* a* b* values for the tile
below
be the same for all filters?)
Some measured values of whites can be found below. Enough layers of paper were
used to have no background shining through. (They are best viewed
with an 8 character tab jump... sorry if it looks bad for you...)
material filter L* a* b*
white ref tile UV 96,2 -0,3 +1,5
U 96,2 -0,3 +1,5
D65 96,1 -0,3 +1,4
(Pol 97,2 -0,2 +1,7)
Proofer materials:
------------------
Iris Semimatte UV 94,5 -1,2 -0,8
U 94,6 -1,1 -1,3
BestGlossy 5150 UV 93,4 +0,8 +0,1
(Epson proofer) U 93,4 +2,3 -5,4
D65 93,7 +3,6 -9,8
(Pol 92,9 +1,5 -0,4)
Book cover materials (cardboard, 240 - 300 g/m2)
--------------------
Invercote-G UV 96,7 -0,2 +2,7
(Sulfatkarton) U 96,6 +0,9 -1,7
Galerie Card UV 94,3 +0,1 +3,5
(Chromokarton) U 94,1 +0,6 +1,5
Parilux UV 95,7 -0,6 +7,8
(yellowish) U 95,5 -0,5 +7,2
D65 95,6 -0,4 +7,1
Starline UV 95,4 -0,4 -0,4
(glossy coated) U 95,2 +0,4 -3,5
(135 g/m2) D65 95,5 +1,2 -6,0
Web offset paper for b&w book content (< 80 g/m2):
--------------------------------------
Werkdruckpapier UV 94,6 -0,2 +15,2
gelblich-wei_ U 94,5 -0,1 +14,3
(yellow-white) D65 95,0 -0,2 +14,2
Werkdruckpapier UV 94,8 +0,3 +7,7
bldulich-wei_ U 94,8 +0,4 +7,6
(blue-white) D65 94,8 +0,4 +7,7
Other:
------
Igepa Copy UV 95,5 +0,7 -1,1
(xerox paper U 95,7 +2,8 -8,3
really glows) D65 96,1 +4,6 -13,8
Kodak Ektacolor UV 92,3 -0,4 +0,4
U 92,4 -0,0 -1,3
D65 92,5 +0,2 -2,3
Kodak Ektacolor UV 95,7 -0,2 +1,4
(after remov. U 95,7 +0,7 -1,8
glossy coating) D65 95,9 +1,4 -4,2
Cheers,
Hanno