Download Week 2 :: Enabling technologies

Multimedia
Week 2 Enabling Technologies
Business and Computing Deanery
Today’s Contents
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Module guide and discuss your
presentation
Enabling technologies
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Digital representations
Hardware and software requirements
Networks
Standards
Look at Flash
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Module guide
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Any questions?
For information on the BBC computer (or
Micro) try http://en.wikipedia.org/
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Presentations
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List of groups
List of subjects
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Analogue or digital?
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What is the difference between music on
a cassette to that of music on a CD?
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Digital representations
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Digital multimedia depends upon the
ability of digital computers to perform
operations at high speed
Image, text, moving pictures and sound
are all reduced to binary digits inside a
computer
Chapman N and Chapman J (2004).
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32–33
Bits and Bytes
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Devices can only be in one of two states
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0 or 1, yes or no, on or off, …
Bit: a unit of data that can only have one
of two values
Byte: an ordered sequence of eight bits
Word: a short sequence of bytes, usually
four (32 bits)
Chapman N and Chapman J (2004).
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Interpretation of Bits
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Numbers to base 2 (binary)
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Characters – associate bit patterns
(numbers) with characters via a character
set
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01100001 = 97 decimal
01100001 = a in ASCII
Brightness of an image at a point,
instantaneous amplitude of a sound
wave, etc
Chapman N and Chapman J (2004).
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Addresses
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Each byte can be identified by its position in
the sequence of all bytes in memory – its
address
Collections of bytes can be combined into data
structures using addresses
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e.g. store an image as a sequence of brightness
values, use address of the first to access the image
data
store a video sequence as series of images, add
address of next and previous to each frame
Chapman N and Chapman J (2004).
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Instructions
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Bit patterns that cause the processor to carry
out operations on values stored in memory
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Hardware is constructed so that the desired effect is
achieved
Programs stored in memory as a sequence of
instructions to be executed in order
A computer is a stored program machine
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It can therefore be used for many different tasks,
depending on the programs it runs
Chapman N and Chapman J (2004).
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Understanding analogue
What is Sound?
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Analogue or digital?
What is the difference
between music on a cassette
to that of music on a CD?
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Analogue and digital
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Describe two types of clock
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Soundwaves
Images used with permission from:
Burk et al (data unknown) Music and Computers, Dartmouth College
[online] http://eamusic.dartmouth.edu/~book/MATCpages/chap.1/1.1.what_is.html [accessed] July 2003
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Analogue to Digital
Soundwave
representation
of music.
Digital
representation
of music.
Winamp is sound software available free from www.winamp.com.
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Converting
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Analogue is soundwaves.
Digital is binary (1s and 0s).
Analogue to digital converter (ADC)
Digital to analogue converter (DAC)
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35–36
Digitization
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Converting a signal from analogue to
digital form
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Analogue signal can vary continuously, digital
is restricted to discrete values
Two-stage process
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Sampling – measure the value at discrete
intervals
Quantization – restrict the value to a fixed
set of quantization levels
Chapman N and Chapman J (2004).
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Sampling and Quantization
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Why is the sampling rate important?
Why is the quantisation level important?
Sampling
Quantisation
Chapman N and Chapman J (2004).
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36–37
Digital Signals
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Only certain signal values are valid
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Relatively immune to corruption by noise
Do not degrade when copied or transmitted
over network
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Some information lost
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Undersampling
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Samples 'too far apart' so cannot accurately
reconstruct original signal
Chapman N and Chapman J (2004).
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40–41
Sampling Theorem
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If the highest frequency component of a
signal is at fh the signal can be properly
reconstructed if it has been sampled at a
frequency > 2fh
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Nyquist rate
Undersamping leads to aliasing
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Sound distortion, image 'jaggies' or Moiré
patterns, jerky or retrograde motion
Chapman N and Chapman J (2004).
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41–42
Too Few Quantization Levels
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Reducing memory requirements by using
fewer bits for each value means fewer
quantization levels are available
Cannot distinguish between values that
fall between levels
Images: banding and posterization
Sound: coarse hiss, loss of quiet
passages, general fuzziness (quantization
noise)
Chapman N and Chapman J (2004).
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Hardware requirements
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Two distinct uses
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Depends what you are going to do
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Requirements for production
Requirements for consumption
For web use?
To display a full feature video
Render 3D animation
What is a multimedia spec for a PC?
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42–45
Hardware Requirements
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Consumption
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Capabilities of typical consumer systems
determine limits of what is feasible
Mobile devices may impose even tighter
limitations
Production
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Highly demanding on processor power,
memory, secondary storage (especially for
video)
Chapman N and Chapman J (2004).
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What do you need?
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Raw processing power
High speed data buses
Large main memories
Powerful graphics and sound cards
Fast high-capacity secondary storage
Chapman N and Chapman J (2004).
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Peripherals
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What peripherals might you need for
multimedia?
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Graphic tablet?
Digital camera
Digital video camera
An extra monitor
Microphone
Transfer of data to the computer
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Firewire
USB 2
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46–47
Peripherals
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High capacity disks connected via high
speed buses
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Firewire 400, Firewire 800, USB 2.0, SCSI III
RAID arrays
Graphics tablet and pressure-sensitive
pen
High-resolution monitor
Digital camera, scanner, DV camera,…
Chapman N and Chapman J (2004).
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Software
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Making multimedia requires a whole host
of software and skills
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Multimedia production often involves a whole
team of people
What type of software do you think you
might need for your portfolio work?
Name examples
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Software Requirements
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Applications for different media types
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Images: image editing, painting and drawing
(Photoshop, Illustrator)
Text: editors, layout programs
Video: editing and post-production
(Premiere, After Effects, Final Cut Pro)
Animation: drawing, interpolation (Flash)
Sound: editing and effects (Audition, Bias
Peak)
Chapman N and Chapman J (2004).
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Software Requirements
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Applications for combining media types
'Authoring systems'
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Timeline-based
May require some programming in a
scripting language to provide interactivity
Chapman N and Chapman J (2004).
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Software we will be using
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Multimedia authoring
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Image editing
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Fireworks
Sound editing
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Flash
Cool edit
Video
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Distribution of multimedia
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Stand alone with a projector with a CD or
DVD
Or over an Network
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Give an example of a network?
How often do you use the Internet?
How important is it to you?
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Networks
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Local area networks (LANs) connect several
computers on one site (Ethernet)
LANs connected together by routers, bridges
and switches form an internet
The Internet is a global network of networks
(internet) communicating via TCP/IP protocols
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Mostly operated by commercial Internet Service
Providers (ISPs)
Domestic users connect via telephone, cable or
satellite
Chapman N and Chapman J (2004).
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51–52
Internet Acess
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Dial-up connection uses modem and analogue
telephone line
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Broadband always-on digital connection (may
be as little as 512kbps, not true broadband)
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V90 modem, 56kbps maximum
ADSL
 asymmetric digital subscriber line
Cable
Satellite
Dedicated line (T1, T3)
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Chapman N and Chapman J (2004).
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Download Times
slow
modem
fast
modem
T1 line
Typical
broadband
T3 line
kbps
(max)
6kB text
page
100kB
image
4MB
movie
28.8
1.5s
28s
19mins
56
1s
14s
9mins
1544
<1s
1s
21s
6000
<1s
<1s
5s
44736
<1s
<1s
1s
Chapman N and Chapman J (2004).
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Clients and Servers
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Servers listen on a communication
channel for requests from clients and
send responses
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Often servers (the programs) run on
dedicated machines, also referred to as
servers
Clients run on separate machines (e.g.
desktop computer)
Interaction is governed by protocols
Chapman N and Chapman J (2004).
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Why Flash?
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“A bandwidth friendly and browser
independent vector-graphic animation
technology. As long as different browsers
are equipped with the necessary plug-ins,
Flash animations will look the same.”
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Webopedia (2005)
Designed for the WWW
Small file sizes
Embed into web pages
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54–56
The World Wide Web
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HTTP – Hypertext Transfer Protocol
Client (Web browser) sends request for a Web
page, server returns it (HTML document)
Identify server and location of page from a URL
http://domain name/path
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e.g.
http://www.digitalmultimedia.org/DMM/index.html
Server may create page dynamically
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Communicates with other program via CGI etc
Chapman N and Chapman J (2004).
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56–57
MIME Types
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Need to identify the type of media data in a
data stream in a platform-independent way
MIME (Multipurpose Internet Mail Extension)
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Originally designed to allow inclusion of data other
than text in email, adopted by HTTP
Content-type: type/subtype
Types include text, image, audio, video, application,
subtypes define specific formats
e.g. text/html, image/gif
Chapman N and Chapman J (2004).
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57–58
Standards
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"Standards are documented agreements
containing technical specifications … to be used
consistently … to ensure that materials,
products, processes and services are fit for
their purpose" (ISO)
Ensure things that conform to standards are
interchangeable
Multimedia standards concern file formats,
markup languages etc, and especially network
protocols
Chapman N and Chapman J (2004).
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58–59
Standards Organizations
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ISO (International Organization for
Standards)
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All technical fields except electrical and
electronic engineering
IEC (International Electrotechnical
Commission)
ITU (International Telecommunications
Union)
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IT dealt with by joint ISO/IEC technical
committee
Chapman N and Chapman J (2004).
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Internet Standards
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Internet Architecture Board (IAB)
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Internet Engineering Task Force (IETF) deals
with technical development
Internet Assigned Numbers Authority (IANA)
registers MIME types, language codes, etc
World Wide Web Consortium (W3C)
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No official status, but Recommendations are
treated as standards for the WWW
Chapman N and Chapman J (2004).
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Some questions
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Scenario: You have been asked by Hope to
create an Library Induction for use by new
students using Flash
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Why would you use Flash?
Why is HTTP important for Flash?
Is a standard browser enough?
Discuss the merits of including a video
Draw up a list of the hardware you would require
Draw up a list of the software you would require
Discuss the process of digitization of media for the
project
Why is the Nyquist rate important?
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For Next Week
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Directed Reading
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Digital Multimedia, Second Edition
Chapters 1 and 2 if you have not read them yet
Chapter 13
Design principles
Chapter 3
Introduction to computer graphics
Independent study
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Finalise your groups
Work on your presentation
Get to know Flash
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Help/How Do I
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􀂃 Work with layers
􀂃 Create a user interface
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What have we covered today?
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Enabling technologies
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Digital representations
Hardware and software requirements
Networks
Standards
Any questions?
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References
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Chapman N and Chapman J (2004).
Digital Multimedia, Second Edition.
London. Wiley pp 7
ISO - International Organization for
Standardization
http://www.iso.org/iso/en/ISOOnline.fron
tpage, accessed 01/10/2005
Webopedia
http://www.webopedia.com/TERM/F/Flas
h.html, accessed 01/10/2005
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