Re: [Phys-l] experiments with dyes (was: happy equinox)

[chuck britton <britton@ncssm.edu>]

What (limited) colors DID the pointillists use????

I suspect that SOME of our non-understanding comes from 'symmantics'  
while other some comes from our mixing the two (valid) viewpoints  
that color represents.

Color sometimes is used to 'describe' the spectral colors 'of the  
rainbow'.
Each of these can be precisely defined by a single wavelength or  
frequency.
Physics classes typically dwell on this 'meaning' of color.

Color is also used in a more widely accepted sense as the PERCEPTION  
of color that results from the stimuli of the cones in the human retina.
The human eye is often considered to be an extension of the human  
brain in that much signal processing is done before the optic nerve  
dumps its information into the 'brain'. PERCEPTION of color indeed  
arises from the stimulation of the 'red', 'green' and 'blue' cones  
and the wavelengths of each receptor overlap with the wavelengths of  
the others.

Anything related to the brain is WAY too important and too  
complicated for any physicist to pretend to understand, yet we must  
pretend sometimes.

Color theorists have been known to state things such as:

	ANY three wavelengths of light can be chosen to represent 'color  
space' as long as two of the 'colors' are additive and one is  
subtractive.

I have no clue as to the relevance or usefulness of this theorem.



On Mar 24, 2008, at 1:08 PM, Michael Porter wrote:

> On Mar 24, 2008, at 12:23 PM, Marty Weiss wrote:
> > Renoir ... must have known
> > a lot about color mixing and while he probably did not *think* about
> > primary colors, like an accomplished pianist does not *think* about
> > *how* to hit the chords on the written score, and race car drivers do
> > not have to *think& about the gears in their trtansmission, and the
> > like, he had to know what to mix to give him the shades he needed  
> > when
> > he went outside.
>
> No argument from me on that -- the suggestion that I took issue with
> was that Renoir et al were claiming that red, yellow, and blue
> specifically were the three primary colours.
>
> ---
> Michael Porter
> Colonel By Secondary School
> Ottawa, Ontario, Canada
>
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