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 (continued)

• 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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Basic Print and Display Concepts

• Share many features
• Character representation methods
• Measurement systems
• Methods of generating color

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Matrix-Oriented Image Composition

• Well take a look at
• Display surfaces
• Fonts
• Color
• Numeric pixel content

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Display Surface

• Commonly used paper, cathode ray tubes, flat
  panel displays
• Divided into rows and columns similar to a large
  matrix
• Each cell (pixel) represents one simple component
  of an image
• Resolution
• Number of pixels displayed per linear measurement
  unit
• Stated in dots per inch (dpi)

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Fonts

• Collection of characters of similar style and
  appearance
• Usually measured in points (one seventy-second of
  an inch), which refers to height of characters

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Color

• RGB (additive colors)
• Generates color by mixing red, green, and blue
• CMY (subtractive colors)
• Generates color using cyan (absence of red),
  magenta (absence of green), and yellow (absence
  of blue)
• CMYK color
• Four-dye scheme using a separate black dye (K)

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Numeric Pixel Content

• Bitmap
• Stored set of numeric pixel descriptions
• Monochrome display
• Displays one of two colors
• Requires only one bit per pixel
• Grayscale display
• Displays black, white, and shades of gray

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Numeric Pixel Content

• Palette
• A table of colors
• Number of bits used to represent each pixel
  determines table size
• Dithering
• Generates color approximations by placing small
  dots of different colors in an interlocking
  pattern
• Half-toning (grayscale dithering)

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Image Storage Requirements

• Depends on number of bits that represent each
  pixel and on image height and width in pixels
• Can be reduced with bitmap compression
• Graphics Interchange Format (GIF)
• Joint Photographic Experts Group (JPEG)
• Moving Pictures Experts Group (MPEG)
• All above compression methods are lossy,
  resulting in some loss of image quality

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Image Description Languages (IDL)

• Address drawbacks of bitmaps (large size and
  device dependence) by storing images compactly
• Can represent image components in several ways
• Embedded fonts
• Vectors, curves, and shapes
• Embedded bitmaps

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Adobe PostScript and Portable Document Format
PostScript PDF
Used in printing and publishing and as graphic file interchange format and embedded printer technology Lacks features needed to generate and manage documents as an integrated whole Ability to distribute compressed documents with complete authorial control over exact format of the printed and displayed document, regardless of end users specific computer, OS, or printer
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Video Display

• Character-oriented video display terminals (VDTs)
• Video controllers
• Video monitors

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Character-Oriented VDTs

• Integrated keyboard and video display surface
• VDTs
• Most common form of video display in 1970s and
  much of 1980s (until PCs)
• Network computers or thin clients
• New class of VDT in 1990s
• Limited processing capabilities

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Video Controller

• Enables communication between computer system and
  monitor
• Accepts commands and data transmitted via a bus
  from the CPU
• Generates TV-style analog video signal, which is
  transmitted to the monitor
• Refresh cycle and refresh rate video RAM dual
  porting graphics accelerators

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A video controller contains RAM, a
microprocessor, and embedded software.
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Video Monitors

• Separate from keyboards
• Common types
• Cathode ray tubes (CRTs)
• Liquid crystal displays (LCDs)
• Plasma displays

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CRT

• Enclosed vacuum tube electron beam is focused
  toward front surface of the tube, which is coated
  in phosphor
• Technology relatively old has disadvantages
• Physical size and weight
• Power consumption

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LCD

• Contains matrix of liquid crystals sandwiched
  between two polarizing filter panels
• Active and passive matrix displays
• Manufactured with thin film transistor (TFT)
  technology
• Compared with CRTs
• Less contrast
• Reduced size, weight, and power consumption
• Higher cost

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How an LCD works
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Plasma Displays

• Combine elements of CRT and LCD technology
• Flat panel, active matrix devices
• Actively generate colored light near surface of
  the display good brightness and viewing
• Require more power than LCDs, less than CRTs
• Shortcomings
• Limited operational lifetime
• Larger pixel size reduces comparative image
  quality when viewed from short distances

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Plasma displays have no backlight and no color
filters each pixel contains a gas that emits
ultraviolet light when electricity is applied.
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Printers
Impact (dot matrix) Slow, noisy Relatively poor-quality output Inexpensive
Inkjet Relatively slow Excellent-quality output
Laser Relatively fast Excellent-quality output
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Inkjet Printers

• Most common printing technology
• Prints with liquid ink placed directly onto paper
• Uses mechanical movement or heat to force ink out
  of nozzle
• Paper is drawn past moving print head
• Resolution is up to 600 dpi

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An inkjet printer has disposable print cartridges
that contain ink reservoirs, a matrix of ink
nozzles, and electrical wiring and contact points.
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Printer Communication

• Impact printers
• ASCII or Unicode characters
• Inkjet and laser printers
• Use pixels as fundamental output unit
• Have relatively large buffers
• IDLs are commonly used to improve printer
  performance

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Laser printers operate with an electrical charge
and the attraction of ink to that electrical
charge.
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Plotters

• Printers that generate line drawings on wide
  sheets or rolls of paper
• Use inkjet technology
• Ideal for blueprints and other engineering
  drawings
• Also called large format printers

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Manual Input Devices
Keyboards For entering text and commands
Pointing devices For pointing and selecting buttons or menu items For drawing For moving the position of cursor
Input pads For many of same functions as mice Also used for signature pads and touch screens
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Keyboards

• Translate keystrokes directly into electrical
  signals
• Generate bit stream outputs (scan code) with a
  keyboard controller
• Can connect to computer in various ways(e.g.,
  PS/2, USB, wireless)

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Pointing Devices

• Mouse
• Trackball
• Joystick
• Input pads (e.g., digitizer tablet)
• Infrared detector
• Photosensor
• Pressure-sensitive pad

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Optical Input Devices

• Detect light reflected off a printed surface or
  object into a photosensor
• Categories
• Mark and pattern sensors
• Image capture devices

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Mark Sensors and Bar-Code Scanners

• Mark sensor
• Scans for light or dark marks at specific
  locations on a page (e.g., standardized
  multiple-choice test)
• Bar code scanner
• Detects specific patterns of vertical bars of
  varying thickness and spacing
• Typically used to track large numbers of
  inventory items

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Advanced scanning technology can now read
two-dimensional bar codes.
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Optical Scanners

• Generate bitmap representations of printed images
• Bright white light shines on the page reflected
  light is detected by an array of photosensors
• Optical character recognition (OCR) devices
• Combine optical scanning technology with
  intelligent interpretation of bitmap content

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Digital Cameras

• Employ optical scanning technology to capture
  single or still images and store them as raw
  compressed bitmaps

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Portable Data Capture Devices

• Combine a keyboard, mark or bar-code scanner, and
  wireless communications to a wired base station
  or computer system
• Provide rapid data capture (e.g., warehouse
  inventory control, package routing and tracking)

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Audio I/O Devices

• Sound an analog waveform that can be sampled and
  stored as digital data
• Various mathematical transformations convert
  complex sounds to a single numeric representation
• Sampling and playback rely on analog-to-digital
  converters (ADC) and digital-to-analog converters
  (DAC)
• Monophonic versus polyphonic

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Purposes of Sound Generation and Recognition

• General-purpose sound output (e.g., warnings)
• General-purpose sound input (e.g., digital
  recording for voice email messages)
• Voice command input
• Speech recognition
• Speech generation

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Speech Recognition

• Conceptually simple, but complicated by speaker
  variability, phoneme transitions and
  combinations, and real-time processing
• Most current systems are speaker dependent
• Digital signal processor (DSP)
• Specialized to process continuous streams of
  audio or graphical data
• Commonly embedded in audio and video hardware

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Speech Generation

• Audio response unit
• Generates spoken messages based on textual input
  (e.g., automated call routing)
• Speech synthesis
• Stores individual phonemes within the system
• General-purpose audio hardware (sound card,
  multimedia controller)

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General-Purpose Audio Hardware

• Typically packaged as an expansion card that
  connects to the system bus of a workstation
• Sound cards include an ADC, DAC, low-power
  amplifier, and connectors (jacks) for microphone,
  speaker, or headphone
• Musical Instrument Digital Interface (MIDI)
• Compact storage format

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Summary

• Concepts, technology, and hardware used in
  communication between people and computers
• Print and display concepts
• Video display devices
• Printers
• Manual input devices
• Optical input devices
• Audio I/O devices