CHAPTER 13 HOW PHOTO-QUALITY PRINTERS WORK^199199
A microprocessor accepts the digital data that make up the photograph, along with any
instructions generated at the onboard controls. The processor applies the changes to the
photo data. It might, for example, add an equal value to each of the digital pixels to
lighten the photograph. With the adjustments made, the processor translates the color
information from the pixels into mixtures of cyan, magenta, yellow, and black needed to
reproduce the digital picture.3
A paper feeder draws a
small sheet of photo
paper from a stack and
starts it traveling down a
paper trainof rollers
that keep the paper mov-
ing at a steady pace.4
The train takes the paper
beneath the path of a long
roll of thin film that is coated
with repeating rectangles of
black, yellow, cyan, and
magenta dyes in a solid form.
Rollers keep the film moving
in precise step with the paper.5
The dye-covered film and the photo paper pass
beneath aprint head made of hundreds of tiny
heating elements poised fractions of an inch above
the traveling roll of dyed film. (This stage is why dye
subs are sometimes called thermal printers.) The
microprocessor, armed with its digital description of
the photograph, sends bursts of electricity to the heat-
ing elements. They instantly soar to precise tempera-
tures. The heat causes the dye to sublimate, changing
it from a solid to a gas without going through the nor-
mal, intervening liquid stage. The clouds of dye fall
on the photo paper and solidify instantly. Depending
on how hot the heating element becomes, the cloud
of dye gas produced is smaller or larger, allowing
the printer to produce subtle tones.6