lecture 2a: analogue to digital evi indriasari mansor tel ext: 1741 1
DESCRIPTION
Learning Outcomes Able to describe the binary numbering system and its relation to the digital data Able to explain the digitization process Able to elaborate the digital representation for multimedia elements 3TRANSCRIPT
Outline Digital Data Digitization Compression Data representation of different media
Images Video and Animation Sound Text Interactivity Metadata
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Learning Outcomes Able to describe the binary numbering system and its
relation to the digital data
Able to explain the digitization process
Able to elaborate the digital representation for multimedia elements
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Based on material fromDigital Multimedia, 3rd EditionPublished by John & Sons, 2009© 2009 Nigel Chapman & Jenny Chapman
These lecture slides © 2009Nigel Chapman & Jenny Chapman
All figures © MacAvon Media Productions
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Analogue and Digital Signals Analogue
Represented by a continuous function Eg.: Analogue sound – finite amount of information (waves)
Digital Represented by a discrete set of values defined at
specific instances of the input domain (time/space or both) Eg.: Digital sound – finite series of instantaneous pulses which
are measured at distinct interval of time
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Analogue and Digital Signals (cont)
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Multimedia in Digital Form The production and consumption of multimedia depends on
the ability of computers to perform operations at high speed In order to benefit from this ability, media must be in digital
form The rich variety of sensory inputs that make up images, text,
sound, animation must be reduced to patterns of binary digits inside a computer Programs can be used to change, combine, store, display, interact with
media all types Data can be distributed anywhere in the world or conveyed to remote
destinations on removable storage (CDs, DVDs or Flash drives)
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A Multimedia System Today8
Multimedia Content creation
Compression & media encoding
Distribution via networks
Different instruments capture different media types in
digital format
S/W & H/WAssembly
Storage
Media server
Cell Phone PDA
Console
Computer
TVCable
Modem
Wireless
Wi-Fi Hotspots
Satellite
Advertising
Digital Rights Management
Subscriber Management
Watermarking
Encryption
Digital Data Computers are built out of device that store and operate
on bits Bits are units of data that can only have one of two
values (0 or 1 / on or off / true or false) Bits are usually groups into larger units such as bytes
which consist of an ordered sequence of eight bits
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Digital Data (cont) Binary System
Binary number consists of 0 and 1 and is fundamental to computer
Can be represented in decimal and hexadecimal for readability 011010102 -> 10610 -> 6A16
Used to represent characters, colors and etc 65 = A, 66 = B 106 = j
Other: brightness of an image or instantaneous amplitude of a sound wave
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ASCII Table – American Standard Code for information interchange. Computers only understandNumbers, so an ASCII code is the numerical representation of a character.
Digital Data (cont) Groups of bits can be interpreted as numbers to base 2,
but can also be treated as characters, colours, etc
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Digital Data (cont)13
Digital Data (cont)14
Digital Data (cont) Decimal to Binary Conversion (example 1)
4 4- 3 2___________________
1 2- 8___________________
4- 4____________________
0
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Digital Data (cont)16
Decimal to Binary Conversion (example 2)
1 5- 8___________________
7- 4___________________
3- 2____________________
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Digital Data (cont) Another more fun way (I think…) Task: Conver 4410 to its binary
representation
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2 44 0 22 0 11 1 5 1 2 0 1 1
22222
Digital Data (cont)18
Digitization Analogue data must be converted to digital form before it can
be manipulated by a computer program
Digitization is the process of converting a signal from analogue to digital form
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Digitization (cont) Digitization comprises two operations
Sampling Quantization
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An Analogue Signal
Sampling & Quantization
Digitization (cont) Sampling
Measuring the signal’s value at discrete intervals The continuous signal is reduced to a sequence of
equally spaced values
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Digitization (cont) Quantization
The process of mapping a large set of input values to a smaller set – rounding values to some unit of precision
The values are chopped off so that every one lies on the defined level
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Digitization (cont)23
Digital signal Sampled and quantized Discrete values
Digitization (cont) Analogue to digital conversion
The process are normally carried out by special hardware device called analogue to digital converters (ADCs)
Digital to Analogue conversion The reverse is performed by a digital to analogue converter (DACs)
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8-channel digital-to-analogue converter (used in soundcard)
4-channel stereo multiplexed analogue-to-digital converter (used in soundcard)
Analogue and Digital Signals (cont)
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ADC DACPROCESSORUnfiltered analogue
signal
Sampled digitized signal
Digitally filtered signal
Filtered analogue
signal
Digital Filters – A digital filters takes a digital signal as input & produces another signal with certain characteristics removed
Digitization (cont) Sampling Rate
The sampling rate is the number of samples in a fixed amount of time or space taken from a continuous signal to make a discrete signal
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Analog signal (blue) with a sampled signal (red) with a fixed spacing or sampling rate
Digitization (cont)27
Digitization (cont) Advantages of Digitization
More robust than analogue signal Do not suffer degradation when being copied or
transmitted in a noisy media
Effect of digitization Some information will be lost
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Digitization (cont) Undersampling
Undersampling leads to aliasing – loss of information during digitization
Perceived in different ways in different media Sound
heard as distortion Images
seen as jagged edges contains fine repeating details (Moire patterns)
Moving pictures jerkiness of motion
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Digitization (cont)30
Insufficient quantization Lead to posterization and Moiré in images (the sampling rate is not high enough to capture the frequency of the pattern)
Brightness contouring Colored areas join together
Quantization noise Sound is quantized to too few amplitude levels
Compression31
Compression Any operation that can be performed on data to
reduce the amount of storage required to represent it Decompression
Restore the compressed data to a form in which it can be used or displayed
Codec Software to perform compression and decompression
Compression (cont) Compression must often be applied to media data Compression may be lossless or lossy Lossless
The algorithm always able to decompress data that has been compressed an retrieve an exact copy of the original data
Less effective Lossy
Some data has been discarded in the compression process and cannot be restored
Only an approximation of the original copy Discarded data often insignificant
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Compression (cont)33
Original data
Compressed data
compress decompress
Original data
Compressed data
compress
decompress
Decompressed dataLossless compression
Lossy compression
Compression (cont) Different compression algorithms are applicable to
different types of media data. Their effectiveness depends on the characteristics of the data itself
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Assignment 1 Develop a website (not more than 3 pages) - Road safety
awareness Provides road safety information for road users Encourage safer behaviour to reduce the number of people
injured & killed on road every year Campaigns:
- Mobile phones - Drug driving- Seatbelts - Drink driving- Motorcycling - Pedestrian crossing- Speed - Vehicle safety inspection
Website not more than 3 pages Dateline : Week 4 :: 6 Oct 2011:: 4pm
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Digital Representation of Media Media is represented in various format:
Images Video Animation Sound Text
The digital media forms need to be represented and stored so that they can be viewed, exchanged, edited and transmitted in a standard manner
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Digital Representation of Media (cont) There are established ways of representing images,
video, animation, sound and text in bits (binary data) with a specific structural form to store information such as length of media data, version and so on
Binary data stored must conform to some file format in order to be processed by software
Many of the most important file formats are associated with particular program. For e.g. most manipulation program can read .jpeg
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Images Image – normally refer to ‘still’ images
Used in various forms – photographs, grey or colour, used with text in documents
Image can be combined to create interesting applications involving mosaics and panoramas
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mosaic
colour
panaroma
grey
Images (cont) All images are represented digitally as pixels
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Images (cont) An image is defined by image width, height & pixel depth The image width gives the number of pixel that span the
image horizontally Image height gives the number of lines in the image Each pixel is represented by a number of bits The pixel depth is the number bit used per pixel in an
image
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Images (cont)42
Monitors displays pictures as a rectangular array of pixels Small, usually square, dots of color which merge
optically when viewed at a suitable distance to produce an impression of continuous tones
To display an image, the program must set each pixel to an appropriate colour or shade of grey
Resolution: the number of pixels in a unit of length Rendering: the process of generating a pattern of
pixels from a model
Images (cont)43
Images (cont) Images may be modelled as bitmaps or vector
graphics
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Images (cont) In bitmap graphics, the image is modelled directly by an
array logical pixels values
Bitmapped image store the value of every logical pixel, so the amount of memory required is based on the size of the image and the resolution at which it is stored
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Images (cont)46
9BB5FF B1CFFF B0D2FF A9CFFF 9FCBFF86B5F9 B0DBFF ADD9FF A9D6FF 9FD3FF7AACEB A0CCFF A6D3FF A1D0FF A0D0FF74A8E2 87B7F9 99C4FF A3D0FF A2D0FF6698D3 6491D5 7AA6EF A1CEFF A5D2FF
Logical pixels Physical pixels
Simple bitmapped image representation
The logical pixels correspond one-to-one to the physical pixels
Images (cont) In vector graphics, the image is stored as a
mathematical description of a collection of individual lines, curves and shapes making up the image
Displaying a vector image requires computation to be performed in order to interpret the model and generate an array of the pixels to be displayed
A simple vector graphic image
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<?xml version =“1.0” encoding=“uft-8”?><!DOCTYPE svg PUBLIC “-//W3C//DTD SVG 1.0//EN” http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/ svg10.dtd><svg xmlns=“http://www.w3.org/2000/svg”> <path fill=“♯F8130D” stroke=“♯1E338B” stroke-width=“20” d=“M118,118H10V10h108V118z”/></svg>
Images (cont)48
Vector graphics are often smaller than bitmaps, are resolution-independent and can be scaled without loss of quality, but they are only suitable for certain sorts of synthetic image, not photographs
A vector drawing and a digital photograph
Images (cont) Bitmap VS Vector
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Video & Animation All current methods of displaying moving pictures depend
on the phenomenon known as persistence of vision for their effect
Persistence of vision A lag in the eye’s response to visual stimuli, which
results in “after-images” being seen briefly when the stimulus is no longer present
If a sequence of still images is presented to our eyes at a sufficiently high rate, above what is called the fusion frequency - we experience a continuous visual sensation rather than perceiving the individual images
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The fusion frequency depends on the brightness of the image relative to the viewing environment (around 40 images per second)
Below this frequency, a flickering effect will be perceived – all illusion of motion is lost and we see the sequence of still images
TWO ways to generate moving picture Sequence of frames from actual motion Creating each frame individually
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Video & Animation (cont)
Video & Animation (cont) Moving pictures can be created as live-action or
animation Live-action
Recording actual motion as it is occurring in the real world
Animation Artificially created sequences (create each frame
individually) Animation may be captured from an external
sources (e.g. a series of drawing) – will produce a set of bitmaped images
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Video & Animation (cont) Live-action must be stored as video
Video frames require a lot of storage so video is invariably compressed for delivery
Animation may be represented in other more flexible or efficient ways (e.g. video, or specialized animation formats which do not have to support the features demanded by video)
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Sound Sound is caused by rapid variations of air pressure over
time, which are detected by the ears Can be translated into electrical signals, using a
microphone, which results in a time varying waveform called audio signal
Digital audio is produced from the audio signal through sampling and quantization
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Sound (cont) Sound can be represented as a sequence of sample after
digitization Digital audio
Recording studio -> CDs -> MP3 player CD audio is sampled at 44.1 kHz, higher sampling rates
are sometimes used Audio delivered over the Internet is compressed, often
using the MP3 codec Digital audio is nothing more than a stream of numbers – it
can be altered using arithmetic operations Easy to apply special effects (e.g. changing the pitch
without altering duration)
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Text A character set is a mapping from characters to
character codes In order for everybody to agree on mapping between
characters and number – need a standard character set
Unicode is a character set capable of representing text in all known languages
A font is a set of character shapes, called glyphs – one for each character in an alphabet
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Text (cont) On computer systems, the font is stored as a collection
of small vector images in a separate file - and glyphs are displayed to the screen as graphics Wide selection of fonts can be provided The appropriate choice of fonts is concerned to best
convey the message in text Many aspects of layout must be controlled when text is
displayed
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Text Layout. The choice of font, the size and weight of the letters and the horizontal and the vertical space between between words making considerable different to the appearance of the text
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Text (cont)
Text LayoutThe choice of font, the size and weight of the letters and the horizontal and the vertical space between between words making considerable
different to the appearance of the text
Interactivity Interactivity is produced by executing a program in
response to user input Program are ultimately represented a bit patterns –
machine instructions Each individual instruction only perform a very simple
operation such comparing or adding two numbers Very few people create programs by writing down the bit
patterns for each instruction – instead they write a description of the computation to be performed using a high-level programming language – incorporate math and logical notations – easily read and written by people
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Interactivity (cont) The program that is written by a person is often
translated into an equivalent sequence machine instruction – known as compilation carried out by a program known as a compiler
In multimedia, programs are often written in a scripting language, such as: JavaScript (used on the web to control the behaviour
of a Web browser) or ActionScript (used to control the Flash Player)
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Metadata Metadata is structured data about data, which may be
attracted to media files to help with searching and classifying them
Metadata is data – can be stored and managed in a database – often called a registry or repository
Metadata is important for media data because it makes organizing and searching feasible
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Metadata (cont) Photograph
Metadata may be written into a digital photo file that identify who owns it, copyright and contact information, the time and date when it was taken, the GPS coordinates of the place it was taken, making the file searchable on the computer / Internet
Photographic Metadata Standards are governed by organizations that following the following standards: IPTC (International Press Telecommunications Council) XMP (Extensible Metadata Platform) Exif (Exchangeable image fiel format) Dublin Core (Dublin Core Metadata)
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Metadata (cont) Video
Metadata is useful in video – the information about its contents (such as transcripts of conversations and text description of its scenes) are not directly understandable by computer – efficient search is required
Sound CDs carry a layer of metadata about the artist, dates,
copyright etc Normally not displayed by CD players – can be assessed
and displayed by specialized music playback or editing applications
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Metadata (cont) Web pages
Webpage may include metadata specifying what language it's written in, what tools were used to create it, and where to go for more on the subject, allowing browsers to automatically improve the experience of users
Most search engines use this data when adding pages to their search index
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Summary Digital data representation Digitization process Compression Data representation of different media
Images Video and Animation Sound Text Interactivity Metadata
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