Graphics Programs Reference
In-Depth Information
RGB model
A large percentage of the visible spectrum can be represented by
mixing red, green, and blue (RGB) colored light in various pro-
portions and intensities. Where the colors overlap, they create cy-
an, magenta, yellow, and white.
Because the RGB colors combine to create white, they are also
called
additive
colors. Adding all colors together creates
white—that is, all light is transmitted back to the eye. Additive
colors are used for lighting, video, and monitors. Your monitor,
for example, creates color by emitting light through red, green,
and blue phosphors.
CMYK model
The CMYK model is based on the light-absorbing quality of ink
printed on paper. As white light strikes translucent inks, part of
the spectrum is absorbed, while other parts are reflected back to
your eyes.
In theory, pure cyan (C), magenta (M), and yellow (Y) pigments
should combine to absorb all color and produce black. For this
reason, these colors are called
subtractive
colors. But because all
printing inks contain some impurities, these three inks actually
produce a muddy brown, and must be combined with black (K)
ink to produce a true black. (K is used instead of B to avoid con-
fusion with blue.) Combining these inks to reproduce color is
called four-color process printing.
Identifying out-of-gamut colors
Colors on a monitor are displayed using combinations of red, green, and blue light
(called RGB), while printed colors are typically created using a combination of
four ink colors—cyan, magenta, yellow, and black (called CMYK). These four
inks are called process colors because they are the standard inks used in the four-
color printing process.
Most scanned photographs contain RGB colors within the CMYK gamut, so chan-
ging them to CMYK mode converts all the colors with relatively little substitution.
