PAPER : PRINTING AND SCANNING

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PAPER PRINTING AND SCANNING

• Presented by
• Nazia
• Mohammed
• Anil

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Printing

• Computer systems have made it easier to produce
  paper documents as it is easy to print out many
  copies in order to get the final copy looking
  just right.
• Older printers had a fixed set of characters
  available on a printhead these varied from the
  line printer to golf-ball and daisy-wheel
  printers.

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continued

• All of the popular printing technologies, like
  screens, build the image on paper as a series of
  dots.
• It enables any character set or graphic to be
  printed, limited only by the resolution of the
  dots.
• This resolution is measured in dots per inch
  (dpi).

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Types of dot-based printers

• Dot-matrix printers
• Uses an ink ribbon, like a typewriter, a line
  of pins are used, each which strike the ribbon
  and result in dotting the paper.
• Ink-jet and bubble-jet printers
• Operate by sending tiny blobs of ink from the
  printhead to the paper. The ink is squirted at
  pressure from an ink-jet, whereas bubble-jets use
  heat to create a bubble.

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continued

• Laser printer
• Uses similar technology to a photocopier
• - dots of electrostatic charge are placed
  on a drum
• - which then picks up toner (black powder)
• - it is then rolled onto the paper and cured by
  heat
• - Curing is why laser printed documents come
  out warm
• Dot-matrix printers have a resolution of 80-120
  dpi
• Ink-jet printers have a resolution of 300-600 dpi
• Laser printers have a resolution of 600-2400 dpi

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Comparing printers

• As well as resolution printers vary in speed and
  cost.
• Ink-jet or Laser printers print between four and
  eight pages per minute.
• Dot-matrix are rated in characters per second
  (cps), printing no more than a page or so per
  minute.

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Fonts and page description languages

• Printed documents can be complex they
  incorporate
• text in many different fonts and many sizes,
  often
• italicised, emboldened and underlined.
• Sophisticated printers can accept a page
  description language, the most common of which is
  PostScript, this is a form of programming
  language for printing.
• Text is printed in a font with a particular size
  and shape. The size of a font is measured in
  points (pt).

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continued

• The shape of a font is determined by the its font
  name, e.g. Times New Roman, Courier, Comic Sans
  MS. Times Roman font is similar to the type of
  many newspapers, such as The Times, whereas
  Courier has a typewritten shape.
• Some fonts, such as Courier are fixed pitch,
  where each character has the same width. The
  alternative is the Times New Roman a variable
  pitched-font, where some characters such as the
  m are wider than others, such as the i.

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Screen and page

• A common requirement of word processors and
  desktop publishing software is that what you see
  is what you get, the acronym WYSIWYG. This means
  the document on the screen should be the same as
  its eventual appearance on the printed page.
• Most screens use an additive colour model using
  red, green and blue light, whereas printers use a
  subtractive colour model with cyan, magenta,
  yellow and black inks, so conversions have to be
  made.

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continued

• Differences between screen and printer mean that
  different forms of graphic design are needed
  for each. E.g. headings and changes in emphasis
  are made using font style and size on paper, but
  using colour, brightness and line boxes on
  screen.
• This is not usually a problem for the display of
  the
• users own documents as the aim is to give
  the user as
• good an impression of the printed page as
  possible,
• given the limitations.

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Scanners and OCR

• Printers take electronic documents and put them
  on paper scanners reverse this process. It is
  started by turning the image into a bitmap, but
  with the aid of optical character recognition can
  convert the page right back into text.
• Two types of main scanners
• - Flat-bed the page is placed on a flat glass
  plate and the whole page is converted into
  a bitmap.
• - Hand-held pulled over the image by hand, as
  the head is passed over an area it is read in,
  yielding a bitmap strip. A roller at the end
  ensures that the scanner knows how fast it is
  being pulled and how big the image is.

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continued

• Scanners work by shining a beam of light at the
  page and then recording the intensity and colour
  of the reflection. Scanners also differ in
  resolution, commonly between 600 and 2400 dpi.
• Scanners are used extensively in desktop
  publishing (DTP) for reading in hand drawn
  pictures and photographs, images can be rotated,
  scaled and transformed using a variety of image
  manipulation software tools.
• Optical Character Recognition (OCR) is the
  process whereby the computer can read the
  characters on the page, scanned images are
  electronically read to convert them into editable
  text. This conversion is performed after
  scanning, and may output formatted text or
  text-files only.