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multimedia
Graphics and Colour
Video and Animation
Sound
Text and Typography
Hypermedia
Flash and DOM Scripting
Multimedia and Networks
nigel chapman and jenny chapman
ThirdEdition
ThirdEdition
digita
l 2Fundamentals
Pocket PDF Key Point SlidesDigital Mult imedia 3rd edit ion
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Based on material fromDigital Multimedia, 3rd edition
published by John Wiley & Sons, 2009
2009 Nigel Chapman and Jenny Chapman
These lecture slides 2009Nigel Chapman and Jenny Chapman
All figures MacAvon Media Productions
Pocket PDF Key Point SlidesDigital Mult imedia 3rd edit ion
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Digital Data
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Bits are units of datathat can only have one of
two values.
A byte is eight bits.
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Groups of bits can be interpretedas numbers
to base 2, but can also be treatedas
characters, colours, etc.
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Analogue data must be convertedto digital
form before it can be manipulated by a
computer program.
Digitization comprises two operations:
samplingand quantization.
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Analogue and digital representations
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Sampling and quantizationAn analogue signal
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The sampling rate is the number of samples in
a fixedamount of time or space.
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The quantization levels are the set of values to
which a signalis quantized.
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Spatialandtemporal signals are made up
of pure sine wave components atdifferent
frequencies.
The Fourier Transform operation can be usedto compute a signals representation in the
frequency domain.
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Square wave transformed
into the frequency domain
0 f-f 3f-3f 5f-5f 7f-7f 9f-9f
y = sin(x)
y = sin(x) + sin(3x)/3
y = sin(x) + sin(3x)/3 + sin(5x)/5
y = sin(x) + sin(3x)/3 + sin(5x)/5 + sin(7x)/7
y = sin(x) + sin(3x)/3 + sin(5x)/5 + sin(7x)/7 + sin(9x)/9
y = sin(x) + + sin(101x)/101
Frequency components of a
square wave
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Higher-frequency components are associated
with abrupttransitions.
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The Sampling Theorem states that, if the
highest-frequency component of a signalis
atfh, the signal can be properly reconstructed
if it has been sampledata frequency greaterthan the Nyquist rate 2 f
h.
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Undersamplingleads to aliasing.
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?
Sampling and undersampling
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Usingtoo few quantization levels leads to
posterization and Moir effects in images, or
quantization noise in sound.
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Moir patterns256, 128, , 2 grey levels
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Posterization
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Compression must often be appliedto media
data.
Compression may be lossless or lossy.
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original data
decompressed data
compressed data
compress
decompress
Lossy compression
original data
compress
decompress
compressed data
Lossless compression
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Different compression algorithms are
applicable to differenttypes of media
data. Their effectiveness depends on the
characteristics of the dataitself.
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Digital Representation
of Media
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There are established ways of representing
images, video, animation, soundandtextin
bits.
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Mediadata may be representedas atextual
description in a suitable language, or as binary
data with a specific structural form.
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Images are displayedas arrays of pixels
and represented usingan internal model.
Generatingthe pixels from the modelis called
rendering.
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An image made up of pixels
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Images may be modelledas bitmaps or vector
graphics.
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A bitmap is an array of logical pixels (stored
colour values) that can be mappeddirectly to
the physical pixels on the display.
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9BB5FF B1CFFF B0D2FF A9CFFF 9FCBFF
86B5F9 B0DBFF ADD9FF A9D6FF 9FD3FF
7AACEB A0CCFF A6D3FF A1D0FF A0D0FF
74A8E2 87B7F9 99C4FF A3D0FF A2D0FF
6698D3 6491D5 7AA6EF A1CEFF A5D2FF
logical pixels physical pixels
Simple bitmapped image representation
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In vector graphics, the image is storedas a
mathematicaldescription of a collection of
individuallines, curves and shapes making
up the image, which requires computation torender it.
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A simple vector graphic image
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Vector graphics are often smaller than
bitmaps, are resolution-independentand can
be scaled withoutloss of quality, butthey
are only suitable for certain sorts of syntheticimage, not photographs.
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A vector drawing and a digital photograph
y
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Transforming the vector image and applying effects to the
bitmap
y
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Scaling a vector image (left) and a bitmap (right)
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Moving pictures can be createdas live-action
or animation.
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Live-action must be storedas video.
Animation may be representedin other more
flexible or efficient ways.
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Frames from an animation
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Video frames require alot of storage so video
is invariably compressed for delivery.
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Sound can be representedas a sequence of
samples after digitization.
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CD audio is sampledat 44.1 kHz, higher
sampling rates are sometimes used.
Audio delivered over the Internetis
compressed, often usingthe MP3 codec.
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A character setis a mapping from characters
to character codes.
Unicode is a character set capable of
representingtextin all known languages.
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A fontis a set of character shapes, called
glyphs.
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A B C D E F G H I J K L M N O P
Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q r
s t u v w x y z
1 2 3 4 5 6 7 8 9 0
A B C D E F G H I J K L M N
O P Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q
r s t u v w x y z
1 2 3 4 5 6 7 8 9 0
A B C D E F G H I J K L M N
O P Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q r st u v w x y z
1 2 3 4 5 6 7 8 9 0
A B C D E F G H I J K L M N O P Q R S
T U V W X Y Z
a b c d e f g h i j k l m n o p q r s t
u v w x y z
1 2 3 4 5 6 7 8 9 0
A small selection of fonts
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Many aspects of layout must be controlled
when textis displayed.
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MOLOREET VOLOREET EX-EROSEtum adionse feuis nonhenim ipsusting etumiriure magna feu feummynis augiam, quat.Minit nibh exer aut au-gait wisim autpat. Utirilit pratisci blam-conse min ullaorper ildeliquamet, volorer os-trud te magna at. Upta-tie dolore doluptat nim
velisci psuscidui tat.Lum veniatum vel initlum velit am dolutat,sissequis numsandreetat.
Moloreet Voloreet Exeros
Etum adionse feuis non henim
ipsusting etum iriure magna feu
feummy nis augiam, quat.
Minit nibh exer aut augait wisim
autpat. Ut irilit pratisci blamconse
min ullaorper il deliquamet, volorer
ostrud te magna at. Uptatie dolore
doluptat nim velisci psuscidui tat.
Lum veniatum vel init lum velit am
dolutat, sissequis numsandreet at.
Layout and typography
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Interactivity is produced by executinga
program in response to user input.
In multimedia, programs are often written in
a scriptinglanguage, such as JavaScript orActionScript.
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Metadatais structureddataaboutdata, which
may be attachedto media files to help with
searchingand classifyingthem.
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