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Chapter 7. Input/Output Technology. Chapter goals. Describe common concepts of text and image representation and display including digital representation of grayscale and color, bitmaps, and image compression techniques

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chapter 7

Chapter 7

Input/Output Technology

chapter goals
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
chapter goals3
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
print vs video display
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
matrix oriented image composition
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
  • 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
pixels and paper
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
  • Printer’s standard is 72 pts per inch
  • This measurement is now standard, although modern printing can apply ink in smaller quantities
pixels and computer display
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
  • 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
poor resolution computers
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
color in video vs print
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
color cont
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
representing colors
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
display restrictions
Display restrictions
  • Size of color palette (number of possible colors)
  • Resolution of the screendemo storage requirements (excel)..\..\Desktop\newmonitor.xls
  • Image representation can be improved through image compression formats (.GIF, .JPEG, .MPEG)
  • Collection of characters in a similar style is called a font
  • Fonts have evolved over the centuries
basic concepts of print and display
Basic Concepts of Print and Display

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

video display
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.
video display26
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

video display28
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

video display30
Video Display

Monitor Types:

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

Printer Types:

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


  • 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


  • 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
manual input devices
Manual Input Devices

Input Devices:

  • Keyboards
  • Pointing Devices
manual input devices37
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.
manual input devices38
Manual Input Devices

Pointing Devices:

  • Mouse
  • Trackball
  • Joystick
  • Digitizer Tablet
manual input devices39
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

manual input devices40
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.
manual input devices41
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.
optical input devices
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
optical input devices47
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
audio i o devices
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
audio i o devices50
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.
audio i o devices52
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
  • 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
  • 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