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[Physltest] [Phys-L] Re: overloaded terms (was: color)



At 01:26 PM 1/29/2005, you wrote:
Frohne, Vickie wrote:
... "Blue" is not, and as far as I know, never has been
a technical term in physics,

John D responded:

Those with wider experience might disagree. This includes
-- Joint Photographic Experts Group (the authors
of the widely-used JPEG standard)
-- Commission Internationale de l'Eclairage (CIE)
-- Society of Motion Picture and Television Engineers (SMPTE)
-- International Color Consortium (ICC)
-- Pantone (the almost de-facto standard for what
inks and process colors are supposed to look like)
-- the "xcolors" utility on my computer

I personally discount the consensus of those with "wider experience"
when it amounts to taking a democratic view of correctness in science.

But this is not John's position, I don't suppose. Rather, he is pointing
to worthy technological institutions who perceived a desperate need
to quantify the usual subjective responses to lights and dyes in respect
to their perceived color.

The physicist notes that the human optical response to color is due to
three broadband light receptors. If she considers two receptors with
overlapping frequency responses, she will acknowledge the possibility
of providing an identical color perception by one low intensity narrow
band stimulus on the peak frequency of receptor A and one high
intensity narrow band stimulus on the far skirt of receptor B's spectral
response.
All the same, she will concede that a medium intensity stimulus off-peak
frequency of receptor A, and a medium intensity stimulus off-peak
frequency of receptor B chosen judiciously, could have the same effect.

Sadly, this multiplicity of stimuli is often unhelpful to the person who
needs to implement color technology: he doesn't want to know of dozens
of ways of invoking a color response; he wants to use a frugal method
of specifying color and its attributes, and this is what he settles for!

Frugality encourages no more color specifiers than the human has
receptor types (fortunately, the animals who feature four receptor
types are not polled for their preference), and economy can encourage
as few as two color poles, if some perceived color degradation is allowed.

In summary, physicists can legitimately specify color in terms of
intensity and wavelength for any number of components and expect
that these objective values are held to be non-negotiable.

But a person working with devices intended to provide a uniform
subjective color response across many users can specify the required
color in terms of quantities in a tri-stimulus diagram of any kind,
even though he knows that the color response is indeed negotiable.
These values are not given [most usefully] in terms of color names
but in number triplets as opaque as the physicist's frequency/intensity
value sets.

I conclude that folks who insist on a definition of blue or magenta or
what ever color as a well-defined physics quantity are mistaken.
They know that there is a line position on a spectrogram of visible light
which can PERFECTLY describe some colors in the objective sense - but
the subjective color sensation can be replicated in many different ways,
and that's what causes arguments, it seems.



Brian Whatcott Altus OK Eureka!
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