Transcript Document

Printing Digital Images
Two Ways to Obtain Prints
• Print them yourself
• Use a printing service
– Local
– Online
Doing Your Own Prints
• Three type of printers available
– Inkjet
– Color Laser
– Dye Sublimation
How Color Images Are Printed
• Color printers create images by dividing a
page into thousands, or even millions, of
tiny dots, each of which can be addressed
by the computer.
• As the printer moves across and down the
page, it can print a dot of color, print two or
three colors on top of each other, or leave
the spot blank (white).
The Two Basic System for
Creating Color
• The two basic system for creating color are
– additive
– Subtractive
• Additive color is used by color displays to
create the images you see.
• Additive color uses red, green and blue
added together in various amounts to
create all of the colors
Additive Color
• Additive color is used by color displays to
create the images you see.
• Additive color uses red, green and blue to
create color images on the screen.
Subtractive Color
• Color printers use the subtractive color
system
• The primary subtractive colors are cyan,
magenta, and yellow.
• By using one or more of the subtractive
primaries on a dot eight different colors can
be produced.
Colors from Subtractive
Primaries
Color 1
White
Cyan
Magenta
Color 2
White
None
None
Color 3
White
None
None
Combined
White
Cyan
Magenta
Yellow
Cyan
Cyan
None
Magenta
Yellow
None
None
None
Yellow
Blue
Green
Magenta
Cyan
Yellow
Magenta
None
Yellow
Red
Black
• A black ink is added to the subtractive
printing system.
• This provide a deeper black then can be
created by the combination of cyan,
magenta and yellow alone
• The name for this color system is CYMK, K
being the black component.
Halftones and Dithers
• On most printers (dye-sub is an exception), each
printed dot has the same density of color.
• If the printer only combined these solid colors, it
would be limited to the eight primary colors for
reproduction.
• To get the millions of colors in a photograph, the
printer has to "fake" the colors by generating a
pattern of small dots that the eye blends to form
the desired shade.
• This process is called halftoning or
dithering and is controlled by the printers
software.
• designing printer software that does
halftoning well is as much art as it is
science.
• Halftoning is done by arranging the
printable dots into grid-like groups, called
cells
• then using these larger cells as a single
unit to print pixels with
• Each cell may be 5 by 5 or 8 by 8 dots in
size.
• The primary colors are combined in a
pattern of dots in these cells, and the eye
perceives them as intermediate hues.
• For example, to print purple the printer
uses a combination of magenta and cyan
dots. For less saturated hues, the printer
leaves some dots unprinted and hence
white in color.
Inkjet Printers
• There are two types of inkjet printers that
can print photographs
• The standard inkjet printer that uses four
inks, cyan, magenta, yellow and black
• Photo inkjet printers that can have seven or
more inks including cyan, light cyan,
magenta, light magenta, yellow and black.
Part of an Inkjet Printer Print
Head Assembly
• Print head - The core
of an inkjet printer,
the print head
contains a series of
nozzles that are
used to spray drops
of ink.
• Ink cartridges - Depending on the
manufacturer and model of the printer, ink
cartridges come in various combinations,
such as separate black and color
cartridges, color and black in a single
cartridge or even a cartridge for each ink
color. The cartridges of some inkjet printers
include the print head itself.
Print head stepper motor
• A stepper motor
moves the print head
assembly (print head
and ink cartridges)
back and forth across
the paper.
Paper Feed Assembly
• Paper tray/feeder Most inkjet printers
have a tray that you
load the paper into.
• Rollers - A set of rollers pull the paper in
from the tray or feeder and advance the
paper when the print head assembly is
ready for another pass.
• Paper feed stepper motor - This stepper
motor powers the rollers to move the paper
in the exact increment needed to ensure a
continuous image is printed.
Control Circuitry
• A small but
sophisticated amount
of circuitry is built into
the printer to control
all the mechanical
aspects of operation,
as well as decode the
information sent to the
printer from the
computer.
Printer Quality
• Determined by the dots per inch that can
be printed by the print head.
• Also depends on how many tones or colors
can be generated in each cell
How Droplets Are Created
• Link to flash movie
Color Laser Printers
• Are more expensive the Inkjet printers
• Supplies are more expensive
• The quality of photos approach the quality
of a good photo inkjet printer
• Have a problem producing glossy prints.
Dye Sublimation Printers
• Where picture quality is very important,
dye-sublimation printers are best.
• The "dye" in the name comes from the fact
that the process uses solid dyes instead of
inks or toner
• Sublimation" is the scientific term for a
process where solids (in this case dyes)
dyes are converted into a gas without going
through an intervening liquid phase.
Materials
• Dye sub printers have their colored dyes in
a transfer roll or ribbon. This roll contains
consecutive page-sized panels of cyan,
magenta, yellow and black dye.
• These printers require special paper that's
designed to absorb the vaporous dye on
contact
How it Works
• During printing, separate passes are made
across the print for each of the four
colors—cyan, magenta, yellow, and black.
• A thermal print head, consisting of
thousands of heating elements, contacts
the media being printed on and vaporizes
the solid dyes.
• What makes these printers unique is that
the heating elements on print head can be
set to any one of 256 temperatures.
• The hotter the temperature, the more dye is
transferred to the paper.
• This precise control of the amount of dye
that's vaporized controls the density or
intensity of the resulting dot on the paper
and produces continuous-tone images.
• Because the dyes are transparent, a cyan
dot may be printed on top of a magenta dot
to make a blue dot.
• By varying the amount of C, Y, and M, any
color within the printer's color range may be
produced.
• Because they can vary the density of each
color, dye-sub printers are the only ones
that don't have to use halftoning or
dithering to create a wide range of colors
Printing Your Own Pictures VS
Printing Services
• Printing your own pictures advantages
– Quicker turnaround
– Control over result
• Printing your own pictures disadvantages
– Cost
– Convince
• Photo Service Advantages
– Cost
– Ease of printing
– Size of prints
• Photo Service Disadvantages
– Instant gratification
– Control