Color and CRT's
If you have a beam of light of one wavelength (say green)
and another beam of another wavelength (say red), they appear yellow to
our eyes but a computer would detect green and red. Is there a way to
combine the wavelenths so that a computer would see green or red or
yellow but never green and red?
The problem isn't in "combining wavelengths", it is just that, for most
computers, yellow simply doesn't exist.
Most graphics hardware in use in computers, define all colors in terms of a
red, green, and blue, component. This system allows a broad range of colors
to be represented, and is called the RGB color space.
Because a computer using the RGB color space only sees red, green, and blue,
it is not possible to have it recognize yellow, even if it is a "pure"
yellow wavelength. In order for the computer to deal with it, it must first
be converted to the RGB color space.
There are a number of different color spaces in use throughout the world.
There are a number of reasons for computers to use the RGB color space. I
think its popularity is due to its simplicity. It is easy (therefore cheap)
to build hardware and software which uses the RGB color space. Since the
RGB color space can represent almost all the colors we can perceive, it has
been a reasonable compromise.
It would be quite possible to make a computer that uses a different color
space, and so is capable of using yellow. In fact, publishing equipment and
printers, are usually designed around the CMYK color space or Cyan, Magenta,
Yellow, and Black, and is just the opposite of the RGB color space. RGB is
designed around turning a light on against a black background. CMYK is
designed around subtracting colors from a white background, which is perfect
for printing ink on white paper.
Anyway, this isn't a direct answer to your question, but I hope it helps.
What the computer 'sees' will depend on the detector that is used. If the
detector is not wavelength specific it will just see an intensity that is the
combination of the intensity from the red and green light.
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Update: June 2012