Re: The DeltaE 2000 color difference formula [was: Evaluation of Color Difference Formulas]
Re: The DeltaE 2000 color difference formula [was: Evaluation of Color Difference Formulas]
- Subject: Re: The DeltaE 2000 color difference formula [was: Evaluation of Color Difference Formulas]
- From: "dpascale" <email@hidden>
- Date: Fri, 20 Jul 2007 10:04:01 -0400
This is the idea!
You mean, why I described is more or less the theory, but the practice is
an
altogether different thing?
No, this was simply a nice description of it!
I am a bit rusty on which differences we humans perceive more readily. I
think the ranking is that we perceive lightness differences first,
saturation second, hue third. Correct?
Maybe. My comment was based on my experience making a lot of these
comparisons. I do not have a handy reference to propose to justify it except
that I suspect the human detection process is faster for lightness than for
chroma or hue. Some of the stuff we see is processed directly in the eye,
other stuff requires the brain; this certainly has an effect on where we
place our priorities and what we "see" first.
They may well first notice the lightness difference and think the other
two
are less in error. They may not realize that they should look at steps in
discernable differences of individual parameters (lightness, chroma,
hue).
Expressed otherwise, they probably "expect" (wrongly) that a 2 deltaE
difference in lightness "looks" similar to a 2 deltaE in hue and, because
they do not look similar, say that these two differences are not the
same.
An observer untrained in color science and unfamiliar with its terminology
may (or not) actually possess an actually sophisticated sense of color
difference. But it's confusing to most, when asked to distinguish among
differences in lightness, hue or saturation, to actually do so effectively
and with a degree of precision without considerable effort. It just
doesn't
come easy.
Agreed, this is why it is difficult to judge of overall match when looking
at many color pairs simultaneously.
To those of us with "average" color vision, a color difference is
perceptible before we are able to describe it, and it's perceived as a
*composite* effect. Its component parts are not easily discernible or
described. Sometimes hue and saturation differences are extremely
difficult
to separate in their effects. It takes training and study for that.
Agreed again, this is why we should transfer some (not all!) of this
responsibilty in the "measured numbers" themselves, which are based on
equations derived from very carefully measured experiments.
Of course, only our customers would do such mistakes, and not us, since
we
know better...
Oh, not at all. I do struggle when I try to describe a color difference
that
I directly perceive with my eyes. And sometimes I struggle when trying to
perceive what others say they are seeing. I know that I have good color
vision, because I tested it, so I do trust my visual perceptions. But I
still struggle a fair bit with the language when describing to others what
I
see (and certainly not because English is a second language for me).
I wanted to be polite since many "non-customers" reading these threads are
more susceptible than you are ;-)
The important thing is that we should all acknowledge that we do not know
everything in color, because:
i- it is a large science field, which mix many specialties. The scientific
expert will rarely have the knowledge require to properly calibrate a
real-life press, and the press expert will often be challenged to explain
why there are different parameters for the CMC or CIE94 formulas.
ii- it is a relatively immature science, which is being improved/challenged
on a daily basis. What was true yesterday may not hold for tomorrow, but may
still be enough for many purposes. CIECAM is an evolution of CIELAB; CIECAM
is being improved; CIELAB is still used (and useful); these are moving
sands!
iii- Numbers are one part of the end result.While they may be sufficient in
many fields, think QC for a manufacturing plant, they cannot characterize
everything we do in color. For example, you may well have a G7 approved
supplier but the output can still look bad for your customer. You still need
that "artisan" touch (and I am not talking of the display here!), which
comes with trial and error, and training, i.e. experience.
On the other hand, we need more than "knowing better" to explain to a
customer that What You Think You See Is Not What You Really See!
(WYTYSINWYRS)
It also boils down to the issue of quality standards. Which in turn has to
do with power struggles as well. *We* as color professionals may wish to
point out to our clients that this or that item doesn't match, but if the
clients are setting the quality threshold low due to their own deliberate
choices (cutting costs being paramount), there is not much we can do. If
they don't care to raise the quality, that's that.
Very true.
Danny Pascale
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