Re: UV filtered vs. non UV filtered spectros
Re: UV filtered vs. non UV filtered spectros
- Subject: Re: UV filtered vs. non UV filtered spectros
- From: Terry Wyse <email@hidden>
- Date: Tue, 29 May 2007 19:04:32 -0400
On May 29, 2007, at 4:25 PM, Todd Shirley wrote:
You say the standard data is "by definition" with UV-included. This
is only relevant if the paper the characterization data was taken
from has optical brighteners, right?
In commercial and even some publication printing, what papers DON'T
have at least some optical brighteners? I would say if your paper
measures -2 b* or greater (numerically), you've got OBs at play. In
the offset printing world, ISO paper types 3 and 5 are about the only
two papers that don't include some OBs.
And when I said "by definition" standard characterization data is UV-
included, that's because that's the standard. In other words, if
you're dealing with standard characterization data in a proofing
RIP, you'll likely have an easier time matching that data using a UV-
included spectro than anything else in my opinion, regardless of
whether the paper has OBs or not. OBs is not JUST about the paper, it
can also affect the ink readings as inks can also have florescent
brighteners added.
The thing about the iSis, as I understand it, is that in order to
take UV-included measurements it actually takes 2 readings of each
patch, using different illuminants, and then does some sort of
averaging to come up with the Lab value. This has the effect of
making the whole device run at half the speed that it runs in UVcut
mode, where it is only making one measurement of each patch. It
also means, in my limited testing, that the UV-included
measurements are somewhat different than the UV-included
measurements off the i1pro, which is only taking one measurement
with no filter, but with a different illuminant.
Yes, that's right. The iSis in "UV-included" mode scans 2 rows at
time with the normal "white" LED illumination and then goes back and
rescans these same 2 rows with the normal illumination off and with a
special UV-emitting LED illuminant turned on. If all you're looking
for is one-or-the-other measurements (UV/non-UV) it takes twice as
long but if you use Measure Tool, at the end of the measurements it
will give you BOTH sets of data that you can save. If you're in the
habit of taking both UV-cut and UV-included measurements, this can
actually save you some time.
I believe the DTP70 (which I don't have) simply has a mechanical
switch for using the UV filter, which means it runs at the same
speed in both modes and just seems to make more sense than the iSis
method. Of course they don't make the DTP70 anymore! The
Spectrolino also seems more logical, in that you just mechanically
change filters. Also no longer in production! And of course your
solution of buying 2 Eye-Ones does has the nasty side-effect of
doubling the price. So you just can't win!
Well, nobody said these decisions would be easy! :-)
But seriously, at least buying two Eye-Ones is cheaper than either an
iSis, DTP70 or Spectrolino.
I was doing some testing just last week (only my second GMG install
using an iSis) and I found that the paper white simulation was fully
5 dE off, most of that in the b* value, when measured with my
unfiltered GMB SpectroEye as compared to the GRACoL2006_Coated1 data
set (paper white 95/0/-2). Fortunately with GMG I was able to apply a
"target value correction" to the original paper white Lab values to
effectively lie to the iSis. After this correction and a couple more
iterations, the paper white simulation was perfect. The point here is
that 1) you need a good UNfiltered spectro to use as a "reference"
instrument to measure and correct for the effects of the UV-cut
measurements and 2) if you're doing proofing, you need a proofing RIP
and/or profile editor that allows you to correct for these effects.
Regards,
Terry
_____________________________
WyseConsul
Color Management Consulting
G7 Certified Expert
email@hidden
704.843.0858
http://www.wyseconsul.com
http://www.colormanagementgroup.com
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