Input/Output Technology

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Chapter 7

• Input/Output Technology

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Chapter goals

• Describe common concepts of text and image
  representation and display including digital
  representation of grayscale and color, bitmaps,
  and image compression techniques
• Describe the characteristics and implementation
  technology of video display devices
• List and describe the three predominant manual
  input technologies

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Chapter goals

• Understand printer characteristics and technology
• Describe various types of optical input devices
  including mark sensors, bar code readers,
  scanners, and digital cameras
• Identify the characteristics of audio I/O
  devices, and explain how they operate

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Print vs. video display

• Print has a thousand year history
• Techniques have developed for the design and
  representation of characters
• Most of these techniques have been transported to
  video display

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Matrix oriented image composition

• Representing text starts with the display surface
• Paper, video, television, computer screens
• Display can be subdivided into rows and columns
  (a table or matrix)
• Each cell in matrix is a pixel

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Pixel

• Smallest element of graphical representation of
  text or image
• Print can be empty or contain one or more inks
  or dyes
• Video empty or display light of varying color
  and intensity

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Pixels and Paper

• Traditionally pixel size corresponds to smallest
  drop of ink that can accurately placed on page
• This is called a point, i.e. 12 pt, 14 pt
• Printers standard is 72 pts per inch
• This measurement is now standard, although modern
  printing can apply ink in smaller quantities

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Pixels and computer display

• Pixel size for modern video display is typically
  between 0.2 and 0.3 millimeters
• Number of pixels on a surface depends on the size
  of the surface (height and width) and size of the
  pixels

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Using pixels to display text
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Resolution

• Important factor in the quality of image
• For print resolution is expressed as dots per
  inch (dpi)
• Laser printers - 600 dpi
• Commercial printing - 1200 dpi
• Screen resolution varies from 640x480 to 800x600

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Image Quality Resolution
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Poor resolution computers

• Computer uses binary information to store
  graphical images
• For each pixel, binary information must describe
  the appearance of the pixel
• Binary information is a representation of the
  color of each pixel

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Color in video vs. print

• Human eye interprets different light frequencies
  as different colors
• Video color is generated directly by the
  display device
• Print color is the light frequency reflected by
  the page

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Color cont.

• Display three primary colors are Red Green blue
  RGB. These three are mixed together to produce
  all colors.
• Print uses subtractive colors cyan (absence of
  red) magenta (absence of green) and yellow
  (absence of blue) plus black, or CMYK

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Representing colors

• Colors are represented in computers using 0s and
  1s
• Each pixel is assigned a fixed amount of bits to
  represent its color, i.e. 24 bits
• Collection of colors that can be represented in
  the available bits is called the color palette

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Color coding examples
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Display restrictions

• Size of color palette (number of possible
  colors)http//www.lynda.com/hex.html
• Resolution of the screendemo storage
  requirements (excel)..\..\Desktop\newmonitor.xls
• Image representation can be improved through
  image compression formats (.GIF, .JPEG, .MPEG)

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Fonts

• Collection of characters in a similar style is
  called a font
• Fonts have evolved over the centuries
• http//www.will-harris.com/type-fun.htm

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Sample fonts
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Font in different sizes
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Basic Concepts of Print and Display

• Vector a line segment that has a specific
  angle and length with respect to a point of origin

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Basic Concepts of Print and Display
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Basic Concepts of Print and Display
Technology Focus
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Video Display

• Character-Oriented Video Display Terminals
• Commonly used during 1970s and 1980s.
• Terminal consist of an integrated keyboard and
  television screen.
• Used today primarily in systems such as retail
  checkout counters and factory floor environments.

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Video Display
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Video Display

• Thin Client a hybrid device with a mix of VDT
  and microcomputer characteristics. They execute
  applications within an operating environment such
  as Java, a Web browser, or Windows Terminal
  Services

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Video Display
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Video Display

• Video Controller accepts the commands and data
  transmitted via a bus from the CPU and generates
  a TV-style analog video signal which is
  transmitted to the monitor

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Video Display
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Video Display

• Monitor Types
• Cathode Ray Tube (CRT)
• Liquid Crystal Display (LCD)
• Plasma Displays

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Video Display
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Printers

• Printer Types
• Impact dot matix
• Nearly obsolete expect for printing multiple
  forms
• Laser
• Inkjet

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Printers

• Ink-Jet
• The print head of an ink-jet printer consists of
  an ink cartridge, a set of ink chambers and a set
  of ink nozzles
• Each ink nozzle can print a single pixel and
  nozzles are arranged in short vertical rows
  similar to those of a dot matrix printer

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Printers

• Laser
• Operates differently from other types of printers
• No print head or ink ribbon is used
• An internal image of the entire page is stored in
  an internal buffer as a bit map.
• Once filled, the buffer contents are sent to the
  print driver for generation

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Printers
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Manual Input Devices

• Input Devices
• Keyboards
• Pointing Devices

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Manual Input Devices

• Keyboard Input
• Keyboard devices translate keystrokes directly
  into electrical signals.
• A keyboard controller is used to generate bit
  stream outputs.
• The controller generates a bit stream output
  according to an internal program or lookup table.

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Manual Input Devices

• Pointing Devices
• Mouse
• Trackball
• Joystick
• Digitizer Tablet

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Manual Input Devices

• Pointing Devices
• Translates the spatial position of a pointer,
  stylus, or other selection device into numeric
  values within a system of two-dimensional
  coordinates

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Manual Input Devices

• Pointing Devices
• Mouse a pointing device that is moved on a flat
  surface such as a table, desk or rubber pad.
• Trackball a mouse with the roller ball on the
  top. The roller ball is moved by the fingertips,
  thumb or palm of the hand.

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Manual Input Devices

• Pointing Devices
• Joystick used as an input device with computer
  games.
• Digitizer Tablet uses a pen, or stylus, and a
  digitizing tablet. The tablet is sensitive to
  the placement of the stylus at any point on its
  surface.

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Manual Input Devices
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Manual Input Devices
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Optical Input Devices

• Mark Sensors and Bar Code Scanners
• Mark Sensors scans for light or dark marks at
  specific locations on a page
• The mark sensors uses preprinted bars on the edge
  of the page to establish reference points

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Optical Input Devices
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Optical Input Devices
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Optical Input Devices

• Optical character recognition (OCR)
• Combine optical scanning technology with hardware
  or software interpretation of bit map content
• The bit mapped representation is searched for
  patterns corresponding to printed characters

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Optical Input Devices
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Audio I/O Devices

• Sound generation and recognition can be used in
  a number of ways
• General-purpose sound output, such as warnings,
  status indicators, and music
• General-purpose sound input, such as digital
  recording
• Voice command input

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Audio I/O Devices

• Speech recognition
• The process of recognizing and appropriately
  responding to the meaning embedded within human
  speech.
• Human speech consists of individual sounds called
  phonemes.

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Audio I/O Devices
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Audio I/O Devices

• Speech Generation
• A device that generates spoken messages based on
  textual input is called audio response unit
• Simple audio response units digitally store and
  play back words or word sequences

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Summary

• Manual input devices include keyboards, mice and
  other pointing devices
• A stored set of numeric pixel descriptions is
  called a bit map
• Video display terminals consist of an integrated
  keyboard and television screen
• Commonly used paper output devices include dot
  matrix printer, ink-jet printer, laser printers,
  and plotters

54
Summary

• Optical input devices include optical scanners,
  mark sensors, bar code readers, and optical
  character recognition devices
• General-purpose speech recognition systems can be
  used for command and control, or for the input of
  large amounts of textual material
• Sound cards include converters, amplifiers,
  microphone, speaker and headphone connectors