Darren New <dne### [at] sanrrcom> wrote:
> On 9/17/2011 18:21, Tim Cook wrote:
> > On 2011-09-17 08:47, Darren New wrote:
> >> I think asking whether it's the eyes or the brain doing the
> >> interpretation is an over-simplified question. :-)
> >
> > Well, was thinking more about the reception of the direct input from the
> > rods and cones, separate any other processing. Sort of a..."is the colour I
> > see as 'blue' the same colour you see as 'blue'?"

> The different rods are definitely responding to different wavelengths. 
> Whether the same wavelengths correspond to the same colors is a different 
> and so-far-unanswered question.  I.e., "blue" is the same wavelength for 
> everyone, but "blue" is a subjective experience.

  It becomes even more complicated when you consider that combinations of
different wavelengths may look the same to the human eye, yet may have
different physical properties (eg. when reflecting from surfaces).

  For example, a light consisting of one single wavelength, pure yellow,
may look to the human eye the exact same color as another light with two
wavelengths, a certain amount of pure red and a certain amount of pure
green. While these two types of light are, physically speaking, completely
different, they may look exactly the same to the human eye (ie. the second
light also looks pure yellow even though it has no yellow wavelength in it
at all).

  (The reason why we are able to see a pure yellow wavelength even though
we don't have "yellow" receptors is that the red and green receptors also
receive wavelengths from around those two wavelengths, including yellow.)

  Even though the two lights look the same color, they may illuminate
surfaces in different ways. That's because surfaces may reflect different
wavelengths in different ways. For example, if we had a surface that
reflected only the pure yellow wavelength, it would look yellow under
the first light but almost black under the second light. (That's the
reason why some lights make everything look "spooky" and unreal. This
is usually because they are composed of a combination of sharp wavelength
curves, rather than being an about evenly-distributed white light that
emits all visible wavelengths almost equally. "White" leds are a good
example of this.)

  Also, there's the fact that the human eye can perceive more colors than
a normal RGB monitor can emit (which means in practice that not all
photographs can be accurately presented with an RGB monitor).

-- 
                                                          - Warp

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