Chapter 7
Input/Output Technology
Chapter goals
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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 goals
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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
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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
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Representing text starts with the display
surface
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Paper, video, television, computer screens
Display can be subdivided into rows and
columns (a table or matrix)
Each cell in matrix is a pixel
Pixel
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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
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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
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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
Using pixels to display text
Resolution
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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
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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
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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.
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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
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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
Color coding examples
Display restrictions
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Size of color palette (number of possible
colors)
http://www.lynda.com/hex.html
Resolution of the screen
demo storage requirements (excel)
..\..\Desktop\newmonitor.xls
Image representation can be improved
through image compression formats (.GIF,
.JPEG, .MPEG)
Fonts
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Collection of characters in a similar style
is called a font
Fonts have evolved over the centuries
http://www.will-harris.com/typefun.htm
Sample fonts
Font in different sizes
Basic Concepts of Print and
Display
Vector – a line segment that has a
specific angle and length with respect
to a point of origin
Basic Concepts of Print and
Display
Basic Concepts of Print and
Display
Technology Focus
Video Display
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Character-Oriented Video Display
Terminals:
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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 Display
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 Display
Video Display
Video Controller – accepts the
commands and data transmitted via a
bus from the CPU and generates a TVstyle analog video signal which is
transmitted to the monitor
Video Display
Video Display
Monitor Types:
 Cathode Ray Tube (CRT)
 Liquid Crystal Display (LCD)
 Plasma Displays
Video Display
Printers
Printer Types:
 Impact – dot matix
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Nearly obsolete expect for printing multiple
forms
Laser
Inkjet
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
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
Printers
Manual Input Devices
Input Devices:
 Keyboards
 Pointing Devices
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 Devices
Pointing Devices:
 Mouse
 Trackball
 Joystick
 Digitizer Tablet
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 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 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.
Manual Input Devices
Manual 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 Devices
Optical Input Devices
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
Optical Input Devices
Audio I/O Devices
Sound generation and recognition
can be used in a number of ways
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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 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 Devices
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
Summary
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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
Summary
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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