Re: Accuracy of instruments
Re: Accuracy of instruments
- Subject: Re: Accuracy of instruments
- From: Mike Strickler <email@hidden>
- Date: Thu, 1 Nov 2007 23:09:56 -0700
Wow, I've gotta get ahold of those glasses you're wearing because
you're reading someone else's thought's in my little paragraph. The
point of course is that the degree of accuracy in measurement you
seek must bear some reasonable relationship to the purpose at hand.
It is not simply the case that more and more accuracy/consistency is
always useful. When the final measure of color is the human visual
system, which has extremely poor repeatability AND interinstrument
agreement (should we also talk about viewing conditions and THEIR
consistency?), there are limits to the usefulness of accuracy of your
spectrophotometers for this application. Perhaps someone could
address what those limits really are. We know this is a complicated
question, and the answer depends on what colors we're talking about,
the degree of variability between observers, ability to control
viewing conditions, and so on. But there is inevitably a point at
which increasing an instrument's accuracy becomes statistically
meaningless. (To give a crude example, you don't need a micrometer to
frame a house.) Perhaps this can be approached empirically: Can
anyone demonstrate a noticeable and objectionable variability in
printed color that can be traced to the performance of any recent
model of spectrophotometer that has passed its manufacturer's
certification process? This is the key: With all of the variables in
play, some with high degrees of randomness, you need to establish
that the instrument was a problem before accusing manufacturers of
indifference to quality.
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Message: 8
Date: Thu, 1 Nov 2007 09:27:03 -0400
From: Terry Wyse <email@hidden>
Subject: Re: Accuracy of instruments
To: "'colorsync-users?lists.apple.com' List"
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Which means...what exactly? That we should let the manufacturers off
the hook for providing better inter-instrument agreement? I believe
that we have very good repeatability these days but I'm not convinced
accuracy is all that good. I've done a few informal comparisons
between my SpectroEye, EyeOne and iSis and suffice it to say that I'm
NOT impressed with their inter-instrument agreement. I've even been
told that my SpectroEye, via NetProfiler, is only certifying itself to
another SpectroEye, not any kind of absolute standard.
Regards,
Terry
On Oct 31, 2007, at 11:26 AM, Mike Strickler wrote:
This comment does not exactly address Roger's complaint, but it may
bear on its relevance. Even if we could achieve higher accuracy in
spectrophotometers, which is problematic for reasons that Robin and
Tom have outlined, let's remember that the standards we're talking
about here are not in the end spectrally-based, but VISUALLY-based.
So we're harnessing a lot of spectral measuring power to get the
most accurate conversion to L*a*b, LCH, XYZ, etc., all of which are
based on some thing far vaguer: the "average" human visual response.
Does anyone have figures for (deltaE) variability between THOSE
instruments?
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