perception and measurement [was: G7 press calibration, best press conditions or average?]
perception and measurement [was: G7 press calibration, best press conditions or average?]
- Subject: perception and measurement [was: G7 press calibration, best press conditions or average?]
- From: Klaus Karcher <email@hidden>
- Date: Fri, 07 Nov 2008 11:52:41 +0100
Paul Foerts wrote:
The eyeballs are used for comparing color and more.
Human vision is the most important element in the evaluation of the
printing process.
Graeme Gill wrote:
I have always found human vision to be the most unreliable of
ways of evaluating color in many situations, a characteristic
common to all the human senses.
hmm ... this might be a bit philosophic, but I think we should not
forget that color is a human sensation by definition.
IMHO the ultimate authority for all those troublesome attempts to turn
color into something physical, measurable, objectively comparable,
absolute, ... must be "the" human perception (which one of the 6.7
billion? under which conditions?).
If a quantity loses touch with perception it is a useless number. It
might still be useful to specify a physical stimulus or property, but it
is no "measure of color".
Our senses are all too easily influence
by moods and expectations (aka biases, and responsible for things like
the placebo effect), and some of the worst possible "instruments"
for doing absolute "measurement".
Yes, but even then our senses are right, but maybe the quantities and
models to quantify the sensations are wrong or inappropriate.
It is very well know and
accepted for instance that human vision tends to adapt to the perceived
white of scene, not something that one would expect of a reliable
instrument.
... but a marvelous gift anyway :-)
While human senses can be very good at comparative judgement,
at times exceeding the sensitivity of instruments in this task,
they are still subject to the bias of expectations, something
that can only be guarded against by using elaborate procedures
such as double blind testing. So the reality is that eyeballs and
instruments need to work together in achieving good color reproduction,
checking each other, used where they have strength, and compensating
for each others weaknesses.
You are perfectly right of course as soon as it comes to repeatability
and comparability, but there are many things to consider when choosing
the quantities. Density for example might be a good measure for certain
physical properties like ink film thickness, but there are definitely
better measures and models to quantify perception.
For creating a repeatable and tight tolerance process though, I certainly
wouldn't rely on eyeballs - they are subject to the frailties of their
owners, and simply aren't consistent enough to be relied on as a reference.
I totally agree.
Klaus
--
Klaus Karcher * Eichenallee 18
26203 Wardenburg * Germany
Tel. +49 441 8859770
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