Printing Digital Images

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Printing Digital Images
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Two Ways to Obtain Prints

• Print them yourself
• Use a printing service
• Local
• Online

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Doing Your Own Prints

• Three type of printers available
• Inkjet
• Color Laser
• Dye Sublimation

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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).

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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

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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.

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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.

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Colors from Subtractive Primaries
Color 1
Color 2
Color 3
Combined
White
White
White
White
Cyan
None
None
Cyan
Magenta
None
None
Magenta
Yellow
None
None
Yellow
Cyan
Magenta
None
Blue
Cyan
Yellow
None
Green
Magenta
Yellow
None
Red
Cyan
Magenta
Yellow
Black
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• 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.

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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.

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• 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.

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• 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.

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• 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.

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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.

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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.

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• 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.

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Print head stepper motor

• A stepper motor moves the print head assembly
  (print head and ink cartridges) back and forth
  across the paper.

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Paper Feed Assembly

• Paper tray/feeder - Most inkjet printers have a
  tray that you load the paper into.

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• 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.

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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.

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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

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How Droplets Are Created

• Link to flash movie

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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.

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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.

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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

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How it Works

• During printing, separate passes are made across
  the print for each of the four colorscyan,
  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.

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• 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.

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• 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

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Printing Your Own Pictures VS Printing Services

• Printing your own pictures advantages
• Quicker turnaround
• Control over result
• Printing your own pictures disadvantages
• Cost
• Convince

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• Photo Service Advantages
• Cost
• Ease of printing
• Size of prints
• Photo Service Disadvantages
• Instant gratification
• Control