Transcript Computer software - Vrije Universiteit Brussel

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Computer software
Overview
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Computer software:
overview of various types
• Computer (disk) operating system(s)
• User interface program(s)
• Utility package(s)
• Local area network software
• Application software package(s)
• Training package(s)
• Data: clipart, sounds, video,...
• Documentation / manual(s) / README files
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Computer software:
between user and computer
User
Operating system shell
Operating system:
Process management
Memory management
File Input/Output
Device Input/Output
Device drivers
Computer
Computer peripherals
Application software
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Computer software
Computer (disk) operating systems
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!? Question !? Task !? Problem !?
List and discuss widespread
computer operating systems.
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Computer operating systems for
microcomputers
• For microcomputers with Intel compatible CPU
»DOS; DOS + Windows 3.x;
Windows 95; Windows 98; Windows 98 SE;
Windows ME,…
»(OS/2)
»Windows NT 4 Workstation; Windows 2000 Professional,...
»Linux,…
• Apple operating systems
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Computer operating systems for
server computers
»Unix (and variants such as Linux)
»Windows NT 4 Server; Windows 2000 server versions;...
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**--
Computer operating systems:
properties
Operating
system
Unix DOS DOS +
OS/2
Linux
Windows 3.x Windows 95
Windows 98
Windows NT
Windows 2000
Multi-user?
+
-
-
-
+
Multitasking?
+
-
-
+
+
Long descriptive
file names?
+
-
-
+
+
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!? Question !? Task !? Problem !?
Why can multitasking on computers
be useful?
(even though people mostly work
on 1 activity at the same time)
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Multitasking:
uses
• Switching among programs
the ability to load several programs and easily and quickly
switch among them
• Running tasks in the background
for instance:
»downloading data,
»printing,
»monitoring disk space,
»receiving electronic mail,...
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!? Question !? Task !? Problem !?
Unix and Linux
have many positive properties,
but have not been used
on most microcomputers.
Why?
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Computer operating systems: Unix:
problems and drawbacks (Part 1)
The code requires more disk space than most operating
systems developed for small personal computers up to
2000.
The system is suited for more multiple users on the same
computer, and therefore it is more complex than most
operating systems developed for small, single-user
personal computers.
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**--
Computer operating systems: Unix:
problems and drawbacks (Part 2)
Does not support as many microcomputers hardware
devices and commercial applications as Microsoft
Windows.
The many versions and interfaces may confuse users.
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*---Example
Computer operating systems: Unix:
character-based interface commands
• cat
Views the contents of text files
• cd
Changes directory
• cp
Copies files
• ls -la
Lists files
• man
Accesses the reference manual online
• mkdir
Makes a new directory
• more
Displays a text file, 1 page at the time
• mv
Moves or renames files
• rm
rmdir
Removes a file
Removes a directory
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!? Question !? Task !? Problem !?
Windows NT4 and Windows 2000
have many positive properties,
but are not used on most low-end PC’s.
Why?
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*---Example
Computer operating systems: DOS:
character-based interface commands
• cd
• copy
Changes directory
xcopy
Copies files
• dir
Lists files
• Mkdir, md
Makes a new directory
• rename
Renames files
• rm
• rmdir
del
Removes a file
Removes a directory
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*---
User interface software for DOS:
some character-based packages
• DOSShell
• PCTools / PCShell
• Norton Commander
• Desqview
• ...
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*---
User interface software for DOS:
some graphics-based packages (GUIs)
• DOSShell
• Microsoft Windows 1, 2, 3.x
• Norton Desktop for Windows
• ...
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Computer operating systems:
evolution
• More user-friendly interfaces
• Increasing power
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Computer software
Graphical user interface = GUI
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Graphical user interface = GUI:
description
The interface on the display is built up using individual
picture elements (= pixels) in an array.
Suitable for the application of WIMP techniques:
Windows,
informative Icons,
a Mouse or another pointing device 8,
Pull-down menus / Pointing
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**--Examples
Graphical user interfaces:
examples
Operating system
Apple Macintosh
Unix
DOS + Windows
Windows 95
OS /2
Windows NT 4
Windows 98
Windows 2000
Graphical user interface
Macintosh System
Open Look, OSF / Motif
Microsoft Windows 1, 2, 3.x
Windows 95
Presentation Manager
similar to Windows 95
Windows 98
Windows 2000
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**--
!? Question !? Task !? Problem !?
Which benefits offer GUIs ?
(in contrast with
character-based interfaces)
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Graphical user interfaces:
benefits (Part 1)
The display can offer better WYSIWYG:
What You See (on the display) Is
What You Get (on printed paper)
The user can change the size of windows on the
information continuously.
The user can choose and use various types and sizes of
characters in the user interface.
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Graphical user interfaces:
benefits (Part 2)
The user can address every single pixel
(using a pointing device such as a mouse)
to generate an action by the computer.
The computer can create detailed icons.
...
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!? Question !? Task !? Problem !?
Which disadvantage
have GUIs?
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!? Question !? Task !? Problem !?
How can WYSIWYG work well?
Why did earlier systems
not offer WYSIWYG as well?
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Graphical user interfaces:
disadvantage
Requires a relatively fast computer system:
»fast processor,
»fast video,
»fast hard disk,
»caching hard- and software,
»...
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!? Question !? Task !? Problem !?
What is easier to do
with a mouse
than with a keyboard?
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Mouse is complementary
to the keyboard
• Drag to change size and/or shape of objects
(windows, graphics, ...)
• Point and click to activate
• Drag and drop:
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»Make selection, drag selection, and paste or put elsewhere
»Select a document by it’s name or icon, drag it to the
program’s name or icon, release the button to make the
program work with the document
»Free-hand drawing
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Computer software
Microsoft Windows: an operating environment
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Microsoft Windows:
an operating environment
Layers for Windows 1.x, 2.x, 3.x:
Application programs + Utility programs
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Microsoft Windows:
benefits with all applications (Part 1)
Offers a graphical user interface for DOS (“shell”).
Allows multi-tasking of programs.
The Windows package includes utility programs.
Due to the multi-tasking, utility programs provided by
Windows can be used by application programs, so that
each application program does not have to offer these
utilities.
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Microsoft Windows:
benefits with all applications (Part 2)
The Windows package includes basic application
programs for
»text editing,
»word processing,
»communications,
»file management,
»calculations,
»bitmap editing,
»...
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Microsoft Windows:
benefits with all applications (Part 3)
Allows cut ", copy and paste of data
»in the same document managed by the same program!
»between various documents managed by the same
program!!
»between various documents managed by various
programs!!!
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Microsoft Windows (all versions):
benefits with Windows applications
Interface is more uniform, consistent, standardised.
Saves time during installation of programs + saves space
on the hard disk, by providing “drivers” for output to
video display(s), printer(s), sound board(s),... which can
be used by all programs for Windows.
Allows software development which is more independent
of display hardware.
DDE / Dynamic Data Exchange among documents
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Microsoft Windows from version 3:
benefits with Windows applications
OLE / Object Linking and Embedding
Provides access to more than 640 K RAM, starting from
version 3.0.
Provides TrueType technology for output to video display
and printer, starting from version 3.1.
Allows drag and drop of files to the icons representing
application programs.
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Success of
Microsoft Windows
“Horizontal” = multi-purpose software  inexpensive 
many millions of copies of this package have already been
distributed internationally.
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Microsoft Windows
tutorials
• Computer-assisted learning about Windows is offered by
the Windows package itself.
• Web-based learning about the basics of personal
computers and about using Windows is available free of
charge from http://www.nassets.com/bb/
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Evolution of Microsoft operating
systems for PC’s
1981
DOS 1
1985
DOS + Windows 1.0
1990
DOS + Windows 3.0
1992
DOS + Windows 3.1
1995
Windows 95
1996
1997
Windows 95 + upgrades
1998
Windows 98
1999
Windows 98 SE
2000
Windows ME
Windows NT 4 Workstation
Windows 2000 Professional
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Computer software
Utility software packages
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Utility software packages:
definition
• Not a well defined term
• One meaning is:
Software which helps to run the computer system,
but which is not directly useful on the application level.
• Operating systems include utility programs;
others can be installed besides these or can replace these.
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Utility software packages:
categories
• Anti-virus scanning and shielding
• Compression / decompression of files
• Archiving / de-archiving of files
• Encoding / decoding of files
• Monitoring CPU-use, disk-space left, disk reading and
writing, battery power in the case of portable
computers,...
• ...
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Computer software
Local Area Network software packages
**--Examples
LAN software packages for
homogeneous networks: examples
• Intel compatible processors:
»LANtastic,
»Novell,
»Windows for Workgroups, Windows 95, Windows 98,
Windows 2000,...
»...
• Apple, ...
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****Examples
LAN software packages for
heterogeneous networks: examples
Based on TCP/IP (protocol suite used in Internet)
• For DOS:
NCSA (= National Center for Supercomputing Applications)
CUTCP, PC/NFS,...
• For Windows 3.x:
PC/NFS, PC/TCP, Trumpet TCP Manager,...
• For Windows 95, 98,...: included!
• For Windows NT, 2000,...: included!
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!? Question !? Task !? Problem !?
Which basic network software
can you use in your institute?
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Computer software
Application software packages
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Categories of
application software packages
• Text editing...Word processing...Desktop publishing
• Spreadsheet
• Presentation creation
• Graphics (bitmap/pixels and vector/object or mixed)
• Multimedia authoring + distribution
• Data communications (basic layers + applications)
• Portable document software
• Database management systems
• ...
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Software for text editing:
categories
• Simple text editors
• Simple word processing software
• Powerful word processing software
• Page-layout software / Desktop publishing software
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**--Examples
Software for word processing:
examples
• For DOS
»Microsoft Word
(Microsoft)
»WordPerfect
• For Windows
»Microsoft Word for Windows (Microsoft)
»WordPerfect for Windows
(Corel)
»Word
(Lotus-IBM)
**--Example
Software for word processing:
screen shot
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Design of documents on paper:
a brief checklist
(Part 1)
• Is the general appearance attractive (not messy)?
• Does the text look well (not squashed up)?
• Do the pages have a basic shape?
• Is there adequate white space?
• Is the line length short enough?
• Are letters in CAPITALS avoided?
• Is underlining of letters avoided?
• Are fonts chosen well?
• Is the character size OK?
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Design of documents on paper:
a brief checklist
(Part 2)
• Is the typography consistent throughout the document?
• Are colours used well?
• Are illustrations/graphics/pictures used well?
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Design of documents on paper:
a brief checklist
(Part 3)
• Is it easy to see the main points?
• Are there a sufficient number of chapter and sub-chapter
headings?
• Are the headings informative?
• Is the number of heading levels not too high?
• Are the differences in heading levels well supported by
differences in formatting of chapter numbers and
characters?
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!? Question !? Task !? Problem !?
Create a document with chapters,
using heading styles.
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!? Question !? Task !? Problem !?
Create a document with chapters,
using heading styles,
and apply outlining.
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!? Question !? Task !? Problem !?
Create a document with chapters,
using heading styles,
and create a table of contents on 1 page,
using styles.
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!? Question !? Task !? Problem !?
What are the benefits
of using styles
in word processing?
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Software for word processing as a
database system: tools
• Styles for paragraphs
(for instance Heading level 1, 2, 3,…)
• Outline view
(hiding levels low in the hierarchy)
• Tables with rows and columns
• Sorting
+ combinations of these
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Software for word processing as a
database system: input methods (1)
• Each (small) database can correspond
»with a whole document created with a program for word
processing
OR
»with a chapter of a document created with a program for
word processing;
then outlining can be used to view and select these
chapters.
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Software for word processing as a
database system: input methods (2)
• Methods to work with database records and fields in
records:
»Using a table
OR
»Using paragraphs formatted with styles
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Software for word processing as a
database system: using a table
• Methods to work with records and fields:
»Each record in one row
»Each field of each record in a column.
(This allows sorting of the records based on the content of
a selected field.)
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!? Question !? Task !? Problem !?
Build a table and
sort the rows (records / items),
based on the contents
of the columns (fields).
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Software for word processing as a
database system: using paragraphs
• Using paragraphs formatted with styles
»Each record consists of several paragraphs.
»Each field corresponds to one of these paragraphs.
(This allows sorting the records based on the first field,
by using heading styles and outlining.)
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!? Question !? Task !? Problem !?
Use heading styles
to create a small structured list,
such as a directory or bibliography.
Use outline view to look at this list.
Sort some records, using outline view.
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Software for word processing as a
database system: retrieval features
• Searching / retrieval / queries can be made
»By sequential string searching
(fast enough with a fast computer and a small database)
(can be slow with a slow computer or a large database)
»Retrieval of record after record; no selection of a record set
»No Boolean retrieval; no positional operators
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***-
!? Question !? Task !? Problem !?
Test the speed of string searching
with the hard- and software
that you use to store information.
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Software for word processing as a
database system: output features
• No sorting or relevance ranking of selected records in
output.
Databases perform better in this area.
• When records consist of several paragraphs together
»using styles for paragraphs allows efficient formatting of
fields in such records
»outlining allows to output only the first parts of records
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**--
!? Question !? Task !? Problem !?
Prepare a printout on 1 sheet of a table with visible borders,
and 4 cells, that contain
1) an image of an animal,
2) the name of that animal,
3) your name,
4) a very brief description of the origin of the animal file
(To avoid that everyone does the same work:
the name of the animal should start with
the same character as your family name.)
**--Examples
Spreadsheet software packages:
examples
• For DOS (without Windows):
»Lotus 1 2 3
»Quattro
»...
• For Windows:
»Lotus 1 2 3
»Quattro
»Excel
»...
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*---Example*
Spreadsheet software packages:
screen shot
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Program types
that handle graphics
• Word processing programs...Lay-out programs
• Presentation programs
• Portable document software
• ...
• Bitmap / pixel oriented editing programs
• Vector graphics / object oriented programs
• Hybrids of the above
• ...
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**--
!? Question !? Task !? Problem !?
Why are bitmaps not ideal
for the storage and distribution
of formatted documents?
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**--
Portable document software:
What is it?
(Part 1)
Ideally, this type of programs
• allows the distribution of a formatted document,
while maintaining the visual integrity of the document
• is independent of computer platform,
(computer, operating system, application software, or
fonts) that is used
»to create the document, and
»to view (read, search, ...) the document
• compresses the document
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**--
Portable document software:
What is it?
(Part 2)
• allows printing the document
• allows searching for character strings in the document
• allows zooming in, without loss of details in the characters
• allows copying text fragments
• allows integration with a WWW browser
• allows hyperlinks / WWW links in the document
• ...
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**--
Portable document software:
applications
• On-line help documents coming with software.
• Electronic publications on CD-ROM and on-line,
in particular when a version printed on paper also exists!
**--Examples
Portable document software:
some programs
• Adobe Acrobat !
»Viewer software is available free of charge
»Software to create PDF files is NOT free of charge;
a free trial is possible through the WWW
• Catchword RealPage
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**--
!? Question !? Task !? Problem !?
Display an existing PDF document;
apply searching for text;
zoom in.
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**--
!? Question !? Task !? Problem !?
Which disadvantages of PDF do you see
(in comparison with other document file formats)?
*---Examples
Software for multimedia authoring +
distribution: some programs
• Authorware
• Iconauthor
• Guide
• Multimedia Toolbook
• Multimedia Viewer
• Tour Guide
•…
+ programs for web development
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**--
Software for database management:
overlapping categories
• Relational
• Object-oriented
• Text-oriented
• Graphics-oriented
• ...
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**--
!? Question !? Task !? Problem !?
Which programs do you know
that can quickly offer an overview
of pictures stored on a pc?
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**--Examples
Software for image database
management: some programs
• ACDSee
Shareware
• Paint Shop Pro
Shareware
• Thumbs Plus
Shareware
• ...
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**--
Speech recognition software:
functions
• Recognition and transfer of spoken commands to other
programs.
• Recognition of spoken text to create documents.
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**--
Speech recognition software

Ariadne / Campbell
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Computer software
General evaluation criteria in the case of
software packages
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**--
!? Question !? Task !? Problem !?
Which general factors
should you consider
in the evaluation / selection of
any software package?
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**--
General evaluation criteria in the case
of software packages (Part 1)
• Which operating system is required by the application
software?
• How good and reliable is the software producer: its
history, reputation, future,…?
How good and reliable is the software supplier /
distributor / dealer?
• How many installations and users are there
»in the country?
»in the region?
»in the world?
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General evaluation criteria in the case
of software packages (Part 2)
• To which extent is the software compatible with hardware
that is already available (such as computers, displays,
printers…)?
• To which extent does the software require new hardware?
• Does the software allow an efficient usage of a mouse?
• Is the software package easy to use? Ergonomic aspects
are important, as training of personnel is expensive and
time consuming.
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General evaluation criteria in the case
of software packages (Part 3)
• Does the program use random access memory and other
computer system resources efficiently?
• Are good and up to date manual(s) for the package
available?
Is an online tutorial (computer-based training) available?
Does the software provide online help? (in context?)
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**--
General evaluation criteria in the case
of software packages (Part 4)
• Is good training and support available in your area, from
the producer directly, or from the distributor, or from
others…?
At what price?
• Is communication with other users easily available for
discussions and to solve problems?
Online? Through the Internet?
• What is the initial price per user, per site…?
• Are regular and substantial updates available?
Online or only offline? At what price?
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General evaluation criteria in the case
of software packages (Part 5)
• Can the user program extensions?
• When some computer system is already used, can
existing, available data be exported from that system and
can they be imported to be managed by the new system?
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**--
General evaluation criteria in the case
of software packages (Part 6)
• Is using an ASP (Application Service Provider) /
networking / co-operation / …
considered as an alternative for in-house implementation
and development of computer software?
Examples:
computer networks for libraries;
electronic mail through the WWW;
…
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General evaluation criteria in the case
of software packages (Part 7)
• How well can data be exchanged with other persons,
institutes, computer systems, databases:
»import of data?
Example: downloading of database records from an
available database/catalogue of books, compact disks,
films, videos…
»export of data?
Example: contributing database records to a union
catalogue of journals, books…
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**--
General evaluation criteria in the case
of software packages (Part 8)
• Is the software compatible with standards used in data
input, import from other systems, export to other
systems,…
Examples:
availability in the case of software for a database system of a
thesaurus module with standard relations among thesaurus
terms;
book database record formatting according to Unimarc for
export to another database;
import and export of HTML files used on a web…
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**--
General evaluation criteria in the case
of software packages (Part 9)
• Is the software suitable for use in an Internet context?
Examples:
create or export files in HTML format to make them available
through the WWW or an intranet;
the creation of e-mail messages by the software to alert users
of problems, things to do…
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***-
Computer software
Introduction to file formats
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***-
The relations between
programs and file formats
Programs to edit/create/develop/maintain a file in a
particular format

File stored in a particular format

Programs to read/view files in a particular format
+ Programs to save=convert=export files from one format
to another
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***-
The program functions
editing, viewing, converting
A program can incorporate only 1, 2, or all 3 of the
functions
• Editing / creating
• Reading / viewing / interpreting
• Converting / saving / exporting
for particular file formats.
***-Examples
Examples of programs
for editing, viewing, converting
Examples:
• Microsoft Word can create/edit + view/read + convert the
file in the formats DOC, RTF, HTML.
• Adobe Acrobat Reader can only view / read
(but not create/edit or convert/save) files in PDF format.
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***-
Computer software
File formats for text only
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***-
File formats for text only:
examples
Type
Normal file name extension
• Files containing unformatted
ASCII text
.TXT
• Files with text coded by the
Hypertext Markup Language
.HTML or .HTM
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**--
!? Question !? Task !? Problem !?
Why can HTML files be considered as text only,
even when many web pages made with HTML
contain graphics/images/photos?
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***-
Computer software
File formats for graphics/images
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**--
!? Question !? Task !? Problem !?
Explain the differences between
bitmap graphics
with vector graphics.
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**--
Graphics formats:
bitmaps and vector graphics
• Bitmap graphics
used in programs for “painting”
• Vector-based graphics
used in programs for “drawing”
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**--
!? Question !? Task !? Problem !?
Draw a small circle with a
paint program for bitmaps and save this.
Draw a small circle with a
draw program for vector graphics and save this.
Select each drawing and enlarge it.
What is the difference between the resulting drawings?
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**--
Graphics formats: bitmaps
compared with vector graphics
Property
Bitmaps Vector graphics
•Suited for “painting”
and “retouching”
+
-
•Resolution adapted
to output medium
-
+
large
small
•Size of files
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***-Examples
Graphics formats
for bitmaps only
File name extension Origin
BMP
GIF
JPG
PCX, PCC
PNG
RLE
TIF
...
Maximum number
of colours
Microsoft
CompuServe / Unisys maximum 256 colours
JPEG
more than 256 colours
Z-Soft Paintbrush
W3C
more than 256 colours
Aldus PageMaker
...
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**--
!? Question !? Task !? Problem !?
Which properties of graphics file formats
for bitmap images are important?
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Graphics formats for bitmap images:
a comparison
GIF
• Maximum number of colours in one image?
JPG
256 256*256*256
• Compression of file size?
+
++
• Compression without loss of quality?
+
-
• Animation possible?
+
-
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**--
!? Question !? Task !? Problem !?
Estimate the typical size of a computer file
that contains a bitmap image in colours,
that has been obtained by using a typical scanner,
and that can cover a complete typical display
or projection screen directly
at optimal resolution without enlargement,
when no compression is applied.
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**--Examples
Graphics formats
for vector graphics (+ bitmaps)
File name extension Origin
CDR
CGM
EPS
IMG
PPT or PPS
WPG
...
Corel Draw!
Graphics Metafile
Encapsulated PostScript
GEM
Microsoft PowerPoint
WordPerfect Graphics
...
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**--
Graphics formats:
the problem of exchange
The differences in all the graphics file formats cause the
requirement of filter / conversion programs, when a
graphics file must be inserted in a document which is
managed by an application program which works
primarily with another graphics file format.
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**--
!? Question !? Task !? Problem !?
Insert a picture, stored in a graphics file,
in a document
created by your program for word processing.
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***-
Computer software
File formats
for documents with text and images
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**--
!? Question !? Task !? Problem !?
Which concrete file formats
for storage of documents
with text and images
do you know?
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***-
Documents with text and images:
available file formats (Part 1)
• Many! Too many?
• Examples:
»formats of the various programs for word processing and
page design, in their various versions (DOC,…)
»Rich Text Format (RTF)
»PostScript (PS)
»Adobe Portable Document Format (PDF);
Catchword RealPage,...
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***-
Documents with text and images:
available file formats (Part 2)
»bitmap-related format, primarily for graphics, but they can
also show characters:
BMP, GIF, JPG/JPEG, PCX, PNG, TIFF...
»SGML, HTML, XML,... considered here together with the
graphics files that they link to
»…
121
**--
!? Question !? Task !? Problem !?
Which properties of computer file formats
for storage of documents
with text and images
do you consider as important?
122
**--
Documents with text and images:
properties of file formats (Part 1)
• Is the format platform independent? (for instance usable
with software on Windows, Macintosh, Unix,…)
• Is the format not proprietary?
• Is the format ‘rich’, allowing to derive less rich formats
from a file in this format?
(for instance
from Microsoft Word to RTF or HTML or PDF,
from SGML to XML to HTML,...)
123
**--
Documents with text and images:
properties of file formats (Part 2)
• Are files in this format small in comparison to the
corresponding files in other formats?
• Is compression applied? If yes, is this compression
without loss of information?
• Are viewers (programs) for users easily available?
• Does the format allow text retrieval? Is the content of a
file in this format searchable on a microcomputer?
• Does the format allow text retrieval by common Internet
indexes? Is the contents searchable through the WWW or
through an intranet?
124
**--
Documents with text and images:
properties of file formats (Part 3)
• Can a file in this format be loaded in a program and be
edited and saved? (or can it only be derived from a
master file in another format?)
• Can the text be reformatted to another size or font?
• Can a selection be made from the displayed contents of a
file in this format, by copy or cut, to be pasted in another
document?
125
**--
Documents with text and images:
properties of file formats (Part 4)
• Does the format not suffer from the existence of various
versions that may confuse the users and that require an
appropriate, up-to-date program?
• Is the format suitable when hard-copy documents are
converted to computer-based documents?
• Is a program to produce the format already available or
not expensive?
126
**--
!? Question !? Task !? Problem !?
Discuss the properties
(advantages and disadvantages)
of each important file format
DOC, RTF, PS, PDF, SGML, HTML, GIF, JPG, TIFF
for storage of documents with text and images?
Summarize all this in the form of a table!
127
**--
!? Question !? Task !? Problem !?
What is the main conclusion
of the overview of the properties
of file formats for storage of text and images?
128
**--
File formats:
the problem of exchange
The differences in all the file formats cause the requirement
of filter / conversion programs, when a file must be
viewed or edited by an application program that is not
exactly the same as the one used to create the file.
129
***-
Computer software
File
compression, archiving and conversion
130
***-
File compression, archiving and
conversion
• Compression
to make files smaller
• Archiving
to keep related
files together
• Conversion
for transfer
via computer networks
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131
***-
!? Question !? Task !? Problem !?
Which benefits are offered
by compression of files?
132
***-
Data compression:
benefits
Storage capacity required on magnetic or optical disks is
smaller
In data communication:
»transmission times are shorter
»transfer of less bits  less network congestion
133
**--
Data compression:
redundancy
Compression is (in many cases) based on the elimination of
redundancy present in the source data:
• Spatial redundancy:
repeated occurrence of the same text or picture elements
• Temporal redundancy:
occurrence of the same picture elements in subsequent
pictures
134
**--
Data compression:
lossless versus lossy
• Compression without loss of data / quality:
“lossless” compression
• Compression with loss of data / quality:
“lossy” compression
135
**--
!? Question !? Task !? Problem !?
Which concrete products,
tools and methods for file compression
do you know?
136
**--Examples
Data compression:
some CODECS
• Compression without loss of data, and archiving:
ARC, BOO, CAB, LHZ, ZIP, ZOO,...
• Lossless compression of bitmap graphics:
GIF, TIFF, ... in various versions
• Lossy compression of graphics with many colours:
JPEG, ... in various versions
• Lossy compression of video with sound:
AVI, MPEG, Quicktime, RM, ... in various versions
137
**--
!? Question !? Task !? Problem !?
Find a file in .ZIP format
and decompress it.
138
**--
!? Question !? Task !? Problem !?
Why is it not useful
to apply a compression procedure
like ZIP for instance,
to a video file
in formats like AVI or MPG?
139
**--
!? Question !? Task !? Problem !?
Which programs do you know
and which program do you use
to save images as JPEG files?
140
**--
!? Question !? Task !? Problem !?
Select or create an appropriate photograph bitmap file.
Save this file as a JPEG file under a different name.
Repeat this at about 3 very different
levels of compression and thus of image quality
(always starting from the appropriate original photo file,
because JPEG is a final storage format).
Load all the resulting photo files in a program to edit such files;
zoom in to 400% for instance;
use tiling to display the photo files simultaneously on the screen;
compare their quality.
Determine also the file size of each photo file.
Decide finally which compression level is appropriate or your aims.
141
****
Essential skills
in computer use
Task
Software used
• File management
• Operating system
• Finding files
• Text editing and
formatting
• Word processing software
(e.g. Word for Windows)
• “Copy and paste” from
• Operating system
one document to the same
+
or to another document
applications software
• Printing