CHAPTER 12 HOW COMPUTERS AND PRINTERS CREATE PHOTOGRAPHS^189
In conventional color printing, four colors are used
to produce the rainbow of the spectrum under a
scheme called CMYK, for cyan (a blue-green),
magenta (a purplish red), yellow, and black(Bis
already taken by blue). These are the colors used
on all printers, although some printers designed
especially for photo printing now have other colors,
such as green and light shades of pink and blue to
increase their gamut, or the range of colors they
can produce.4
Photo printers create images by one of two ways.
Some lay down tiny dots of ink thickly or thinly,
depending on how dark a shade they need to
reproduce. The printers might employ different pat-
terns of dots called ditheringto disguise the fact
that a color is changing from one shade to
another. The newest inkjet printers are capable of
varying the sizes and shapes of the dots they pro-
duce to more effectively produce gradations and
shades of color. Other printers produce
continuous tone, which more closely resembles
airbrush work in that there is no perceptibly abrupt
change from one color to another.5
To mix inks to create different colors, a continuous tone printer lays
down its inks or dyes on top and overlapping one another. In conven-
tional color printing (such as a printing press) and in most types of
laser printing, CMYK inks and toners can’t be varied continuously in
an image. Instead, the printer usually simulates the color variations
withhalftoning. It prints CMYK ink dots of varied sizes in overlap-
ping grids that are laid out at different angles so all the dots don’t print
directly on top of each other. The always accommodating human eye
completes the job of blending the dots into a single perceived color.6