Re: Metamerism vs Color Inconstancy, again
Re: Metamerism vs Color Inconstancy, again
- Subject: Re: Metamerism vs Color Inconstancy, again
- From: Marco Ugolini <email@hidden>
- Date: Mon, 21 Jun 2010 21:47:31 -0400 (EDT)
Graeme Gill wrote:
>Marco Ugolini wrote:
>
>> "Related to metamerism is COLOR CONSTANCY, the tendency of an object to
>> maintain its color despite changes in illuminating conditions. Each object
>> forming a metameric pair has a different DEGREE OF COLOR INCONSTANCY. For
>> example, the right-hand square [of two squares viewed under one illuminant
>> -- MU] will turn pinkish when illuminated by incandescent illumination,
>> whereas the left-hand square tends to remain grayish. Although both samples
>> match under daylight and are thus a metameric pair, only one sample of the
>> pair exhibits objectionable color inconstancy. If both formulations [both
>> specimens -- MU] are candidates as a color standard, the sample that
>> minimizes the degree of color inconstancy would be preferred."
>>
>> Roy Berns, "Billmeyer and Saltzman's Principles of Color Technology", Third
>> Edition, Wiley & Sons, 2000, page 29
>>
>> It's all there: the distinct notions of metamerism vs color
>> constancy/inconstancy, and their correlations too.
>
>I think you are reading far too much into this.
Berns is too, apparently. Shouldn't we tell him?
>Color constancy is not related solely to metamerism, but is a far wider topic,
>mainly to do with human vision and perception.
Do we really need to make things more complicated than they need to be for the topic at hand? Whatever else is tied to this concept, in the quote Berns talks about color inconstancy IN THIS CONTEXT, not in that of discounting the illuminant and so forth.
Can we please just stay on topic and not divert the topic, specially when this "wider" meaning does NOT invalidate the meaning presented here?
>Naturally a color that
>remains close to a metameric match under different lighting
>conditions is going to be more perceptually constant in color
>(which is what Roy Berns is saying above), but the reverse is not
>necessarily the case.
I really fail to grasp your meaning ("the reverse" of what?). Berns is saying that a highly color-inconstant sample will tend to differ from a far more color-constant reference sample more markedly upon a change in illuminant (the left-hand square - the reference - remains grayish, whereas the right-hand square - the match/non-match - turns pinkish under incandescent).
>You may well have a situation in which a
>change in lighting induces large metameric failures (compared
>to the target colors), but perceptually remains a constant color.
But that would be because the reference is color inconstant as well, wouldn't it, whereas Berns makes the case of a (relatively) color-CONSTANT reference sample (from one illuminant to another).
>So to say that a failure of a color to match a target due to a
>change in lighting conditions is "color inconstancy" is not
>being very specific as to the cause. Color inconstancy can be
>due to many other things than metameric failures.
But color inconstancy is NOT due to metameric failure. The latter is not its CAUSE: metameric failures occur because one or both samples present a degree of color inconstancy.
>"Metameric failure" is being specific, and isn't confusing
>the situation by dragging in unrelated phenomena.
"Specific"? "Unrelated phenomena"? How is color inconstancy "unspecific" or "unrelated"? Care to expand?
>For a broader view on color constancy, take a look at the
>work of some of the primary researchers in this area, e.g.
>McCann <http://web.me.com/mccanns/Color/Color_Constancy.html>.
>You'll notice that the emphasis is on many aspects of vision,
>but has little directly to do with metamerism.
How does this work on color constancy negate or make invalid the meaning of color INconstancy explained by Berns? (...which is the meaning that I have been trying to expound upon, against rationally unexplainable opposition on this forum, seemingly more interested in finding reasons to counter it, however elaborately strange these reasons may be, rather than in conceding this quite uncomplicated point of distinguishing conceptually between "metamerism" and "color inconstancy".)
The fundamental reason for this opposition eludes me, since, to me, so far the rational argument for distinguishing color inconstancy from metamerism has not been proven either invalid or inappropriate in any persuasive manner.
Marco Ugolini
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