Re: Question: Measuring Delta E from two different spectrophotometers (odd problem)
Re: Question: Measuring Delta E from two different spectrophotometers (odd problem)
- Subject: Re: Question: Measuring Delta E from two different spectrophotometers (odd problem)
- From: <email@hidden>
- Date: Fri, 25 Aug 2006 14:27:05 -0400
Hello Richard,
I have seen the exact same phenomenon when measuring
yellow, orange and red BCRA tiles with five different
instruments (including a NIST traceable one). Some
instruments gave errors in the 7-8 DeltaE range (CIELAB)
relative to the NIST traceable measurements, while others
were in the less than 1 DeltaE range.
All these colors have very sharp cut-off slopes, and this
spectral characteristic makes the mesured color very
sensitive to small spectrometer wavelength calibration
shifts.
First, get away from CIELAB. You will measure smaller, by
a factor of two plus, and more realistic, compared to
visual assessment, color differences using CIE94 or
CIEDE2000. Still, you probably will not achieve the less
than 1 DeltaE target.
You may want to look at an inter-instrument calibration
solution, such as netprofiler from GMB, but this one in
particular may not be compatible with the instruments you
have.
I have also done inter-instruments matching on my own,
using from 8 to 30 samples, and have improved matching in
all cases (a factor of two improvement is not uncommon).
The Xenon vs LED may also be the cause of the problem
since the Xenon is likely to generate more fluorescence.
Can you try a UV filter on the Datacolor?
Danny Pascale
email@hidden
www.BabelColor.com
On Fri, 25 Aug 2006 12:40:21 -0500
Richard Brackin <email@hidden> wrote:
We have supplied identical (or as close as it can get)
color standards to some manufacturers.
We are all measuring L*a*b* values of a series of films
against those standards, (Green, Blue, Red, Purple, Gray,
and Orange, etc.).
We, as well as their color laboratories, are taking
measurements on these very specific pigmented colors and
we're all using different measuring devices.
In discussing the issue with the head of color matching
at one lab, we are seeing similar (not extremely close,
but similar) L*a*b* measurements for the standard.
However, we're all seeing color variances of approx 1
delta E on all of the colors except this particular
orange.
While they are seeing 1 delta E comparing the orange to
the standard, we're seeing 13 delta E.
We're measuring Delta E (CIE 1976) D50 at 10 degrees.
(CIE 1994 Graphics shows approx 6 delta E but we've been
asked to use CIE 1976).
What are some factors that would make one color show up
so differently?
Should we be using a different color model for
measurement?
The standard probably has a variance of 0.5 delta E
across the surface.
They are using DataColor SF600 Plus and we're using
BYK-Gardner ColorGuide Sphere.
The Data Color uses Xenon, the ColorGuide uses LED.
Could the pigments used to make their orange color cause
such a drastic difference in measurement between the two
light sources?
many thanks
Richard
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