Computer
monitors are based on cathode ray tubes (CRTs). CRTs comprise an electron
"gun" which beams electrons on to a surface coated with phosphorescent material
(the screen). When the electrons hit the the screen the phosphors glow,
if no electron strikes the screen the phosphors remain dark. The beam zigzags
across the screen while it also moves from top to bottom. The combination
of these movements and the alternation of light and dark dots produce the
image. Modern colour monitors work on the same principal but use three electron
guns to produce the illusion of full-colour. Because they use light to produce
an image their colours fall into the additive colour gamut.
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Computer
monitors project beams of red, green and blue light through a mesh to form
tiny pixels (or picture elements) on the screen. To control the colour of
each pixel on the screen the computer's operating system must dedicate a
small amount of memory to each pixel. The simplest computer display will
dedicate a single bit of information to each pixel. A memory bit can only
be positive or negative (0 or 1) thus such a system can  only
produce two colours (black or white) for each pixel.
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The
simplest computer display will dedicate a single bit of information to each
pixel. A memory bit can only be positive or negative (0 or 1) thus such
a system can only produce two colours (black or white) for each pixel.
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When
eight bits of information are dedicated to each pixel a computer monitor
can display 256 colours. 256 is the maximum number of unique combinations
of 0's and 1's achievable with eight bits of information. These colours
are referenced to a "palette" or "index" and are sometimes called indexed
colours. These colours are those used by HTML and GIF-format graphics so
are particularly important in web design. |
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A computer
can obtain nearly photographic colour by dedicating 24 bits of information
to each pixel; eight each for the red, green and blue components. Such
displays are called "True-colour" or "24-bit colour" and can show millions
of colours simultaneously.
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are limitations when using computers to design for print. These come about
because RGB colours and CMYK colours are created differently, and have their
own characteristics. Each is incapable of producing certain colours that
exist in the other spectrum. The colours that exist in each spectrum are
known as the "colour space" or "gamut", and may be refered to as the RGB
gamut or CMYK space. |
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References:
An Introduction to Digital Colour Prepress -Agfa Educational Publishing,
USA, 1997
Yale Style
Manual: Colour
display guide
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and graphics: John Bleaney and Shiralee
Saul 2001 |
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