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Only 3 colours?

Stephen H. Westin westin*nospam at graphics.cornell.edu
Mon Mar 25 10:10:54 EST 2002

"Neil" <neil_delver at hotmail.com> writes:


> The point I want to make is how interesting it is that we experience
> those "fundamental looking" colors, which don't "appear" mixed with
> something else. That is what the names really refer to, and they
> presumable would come from stimulating only that one cone type - so
> it seems the old names were right after all in the sense that
> counts.

No, it's very hard, in fact, to stimulate the L and M cones
separately. Most of their sensitivity overlaps. See, for example,
<http://www.yorku.ca/eye/specsens.htm> or
<http://aris.ss.uci.edu/cogsci/courses/psych9b/lectures/lec4notes.html#spectral_sensitivity>. The
two peaks are only 30nm apart.

> Indeed, from that point of view, we really have four primary
> colors since yellow doesn't look like it's made of red and green -
> we don't call any colors "reddish-green" etc.

But from a mathematical point of view, three dimensions are sufficient
to describe normal human color perception, since it all is mediated by
three kinds of cones.


-Stephen H. Westin
Any information or opinions in this message are mine: they do not
represent the position of Cornell University or any of its sponsors.

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