[Tutor] How do you make yellow?

[Magnus Lycka]

Since it's Saturday, I allow myself to get a bit off topic. ;)

At 17:40 2002-11-22 -0500, James M Lang wrote:
>While trying to figure out how to change colors from the example on the 
>livewires package, I was wondering how a TV would create yellow, 
>considering that it only has red, green, and blue. It's been mystifying me.

First of all, colours in nature is normally indicators of
various wavelengths of electromagnetic radiation in the
range from roughly 400 to 700 nano metres, or 0.0004 to
0.0007 millimetres. See
http://imagers.gsfc.nasa.gov/ems/visible.html
http://www.howstuffworks.com/light.htm/printable

The short answer is that the TV *can't* create yellow. A TV
only shows red, green and blue fields on the screen. It makes
you imagine that you see yellow by performing a trick based on
an understanding of how the eye is constructed. With the right
mix of red and green sufficiently close to each other, the eye
will imagine that it sees yellow. If you look really closely at
your TV you will see these red, green and blue fields. (For a
computer screen I think you need a magnifying glass to see these
fields.) See http://www.howstuffworks.com/tv.htm/printable

The eye has four kinds of light receptors, three of which are
sensitive to different colours, with maximum sensitivity at
red, green and blue. It's the proportion of signal strength in
these colour sensitive receptors that determine how the brain
imagines colours.

See http://www.cecs.csulb.edu/~jewett/colors/index.html
http://www.cis.rit.edu/mcsl/faq/faq1.shtml
http://www.yorku.ca/eye/toc.htm (Chapter 6)
http://www.brunel.ac.uk/~castjjg/hndcfund/material/graphics/graphics.htm



-- 
Magnus Lycka, Thinkware AB
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