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Subtractive Theory
A printer's output reflects light. It usually begins with white (paper)
and creates color by laying down inks that absorb (or subtract out)
specific proportions of red, blue, and green light. Cyan ink subtracts
out all red, magenta subtracts out all green, and yellow subtracts out
all blue. Adding all three inks in equal quantities, theoretically
creates black. However, manufacturing limitations prevent the inks
from creating a true black, so most printing systems add a black ink
to the three primary subtractive colors. Using Cyan, Magenta,
Yellow, and Black inks to subtract out red, green and blue
wavelengths is referred to as CMYK printing.
Ink Density Variables
When you print in color, the ink density as well as the reflection and
absorption capabilities of the media can affect the output. (See
"Media Variations" later in this chapter for more details.)
To compensate for density, ink/media differences, and printer
conditions XANTÉ created special color rendering dictionaries
(CRDs) and a Transfer Curve feature for use with the Accel-a-
Graphix CT4.
CRDs
Color Rendering Dictionaries convert the RGB data produced by
scanners, monitors, and photo CDs to CMYK data used by color
printers These files define the creation of specific colors in various
ink, printer, and media environments.
XANTÉ CRDs cover some of the most commonly used
combinations of printers, inks, and media. These CRDs should
suffice for most jobs when the corresponding ink, printer, and media
are used. To further fine-tune the output, use transfer curves to
compensate for environmental conditions and individual printer
differences. See "Media Variations" and "Printer Variations" later in
this chapter and "Color Management" in chapter 8 for additional
information.
7-6 Imaging Basics _______________________________________
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Troubleshooting
