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: Marco Ugolini <email@hidden>
- Date: Thu, 19 Jul 2007 21:45:39 -0700
- Thread-topic: The DeltaE 2000 color difference formula [was: Evaluation of Color Difference Formulas]
In a message dated 7/19/07 9:08 PM, dpascale wrote:
> Marco,
>
> This is the idea!
You mean, why I described is more or less the theory, but the practice is an
altogether different thing?
> Now, in practice, if you would ask your customer to judge three color pairs,
> each with, lets say, a 2 deltaE difference, but each from a different
> parameter (i.e. 2 deltaE due to lightness, or 2 deltaE due to saturation
> (chroma), or 2 deltaE due to hue) will he/she recognize that these are
> differences of the same amount?
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?
> 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.
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.
> 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).
> 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.
Marco Ugolini
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