### Re: Why sixteen million colors?

Date: Thu Oct 14 23:05:42 1999
Posted By: Matthew B. Weyerich, Technical Coordinator,ES&R Dept., CPI Corp.
Area of science: Engineering
ID: 939160578.Eg
Message:
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Hi, Brent!

Can our eyes do better than the 16 million colors of "true color"? You bet,
but not for the reasons you may think!

First of all, your screen isn't really working with 16 million colors. It's
using THREE: red, green, and blue. If you perceive yellow on your screen,
you're actually looking at red and green phosphor dots. This is an example
of the principle of additive color. (There's no "yellow-wavelength" light

The "16 million figure" has more to do with your computer than your
monitor, or, your eye. Computers only understand "on" and "off", or, 1 and
0. If you want a computer to work with an advanced concept like "yellow",
you have to describe this in terms of ones and zeros, or "bits". How best
to do this?

We know our monitor works with three colors, red, green, and blue. If we
represent each color with eight bits (one byte), we'd be working with a
total of 24 bits. Each bit can be on or off, so we have 256 possible
combinations of on/off for each byte/color (8 bits) and a grand total of
16,777,216 possible combinations of 1's and 0's. There's nothing "magic"
to divvy up the visible spectrum, using additive color and different
saturations and intensities of red, green, and blue. (In other words, there
should be 16.7 million different shadings and intensities in 24-bit color.
There aren't that many actual wavelengths used.)

16.7 million is a pretty good sampling of anything, but it turns out not to
be good enough. Your monitor simply can't display some colors. The color
gamut of most monitors is smaller than that of photographic film, and
certainly smaller than that of the human visual system. (A color gamut is
often plotted on a CIE color diagram. The CIE colorspace was developed from
human descriptions of perception of color, so we see all the colors.) So,
the human eye DOES do much better than 24-bit color.

The visible electromagnetic spectrum is usually considered continuous, so
there should be an infinite number of possible wavelengths and colors.
However, I've seen good argument for 300 trillion as a ballpark figure for
the number of possible colors.

There's still a great deal to learn about the perception of color, because
no one knows exactly what happens after the light strikes the back of your
eye. We have some idea of the mechanics, but we're a long way from figuring
out how we get "yellow" (as a concept) out of this.

I've placed some links you may find useful below. They'll teach you more
about all of this. (There are more. E-mail me if you need references.)

I hope I've helped with your questions!

-Matt
mwnet@swbell.net

True Color definition

How many colors?

MOST EXCELLENT SITE TO LEARN ABOUT COLOR
(I  very lucky to get to work with those good folks all the time! Learn
from the true masters, my friend!)

Color "slides"

A colorful site

What the journalists are saying

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