digitization of audio.ppt
TRANSCRIPT
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Chapter
Overview of Analog and Digital Technologies
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Chapter Objectives• Explain the basic concepts of analog and
digital technology • Show the importance of frequency spectrum to
communication along with an explanation of the concept of bandwidth
• Give an overview of the interface technology between analog and digital technology
• Describe the process of digitizing data, audio, image and video
• Discuss quality retention in digital transmission
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Chapter Modules
• Overview of analog technology• Frequency spectrum and bandwidth• Digital technology• Digital-to-Analog and Analog-to-Digital
Interfaces• Overview of Digitization of Information• Digitization of Data • Digitization of Audio Continued
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Continuation of Chapter Modules
• Quality retention in digital transmission
• Digitization of image• Digitization of video
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MODULE
Overview of Analog Technology
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Areas of Application
• Old telephone networks• Most television broadcasting at
present• Radio broadcasting
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Analog Signals: The Basics
Cycle
Time
Signal
Amplitude
Frequency = Cycle/Second
A typical sine wave
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Amplitude and Cylce
• Amplitude– Distance above reference line
• Cycle– One complete wave
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Frequency
• Frequency– Cycles per second – Hertz is the unit used for expressing
frequency
• Frequency spectrum – Defines the bandwidth for different
analog communication technologies
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Information Representation Using
Analog Signals• Information can be represented
using analog signals• Analog signals cannot be
manipulated easily• Analog signals must be digitized
for computer processing
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Analog Digital Conversion
1 0 1 1 0 1 0 0
A to D Converters, Digital Signal Processors (DSP)
etc.
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Data Transmission Example
Computer ModemDigital0s and 1s
Analog0s and 1s
Digital-to-Analog Modulation and vice versa
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Voice Transmission Example
Voice
Carrier Wave
AM Radio Transmission
Analog-to-Analog Modulation
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END OF MODULEEND OF MODULE
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MODULE
Frequency Spectrumand Bandwidth
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Frequency Spectrum Defined
• Available range of frequencies for communication
• Starts from low frequency communication such as voice and progresses to high frequency communication such as satellite communication
• The spectrum spans the entire bandwidth of communicable frequencies
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Frequency Spectrum
Low Frequency High Frequency
Radio Frequency
CoaxialCable
MHz
SatelliteTransmission
MicrowaveMHz
Voice
KHz
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Frequency Spectrum
• Low-end– Voice band
• Middle– Microwave
• High-end– Satellite communication
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Bandwidth Definition
• Bandwidth, in general, represents a range of frequencies
300 MHz 700 MHz
Bandwidth is 400 MHz
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Usage of the Term Bandwidth
• To specify the communication capacity– A medium such as a coaxial cable is
associated with a bandwidth
• To indicate the bandwidth of a technology– Voice grade circuits have a bandwidth
of 4 KHz (0-4000 Hz)
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Communication Capacity
• Bandwidth is indicative of the communication capacity
• Communication speed is proportional to bandwidth– Shanon’s law
• Units used to represent bandwidth are MHz, Mbps etc.
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Coaxial Cable Example
• Bandwidth of 300 MHz • Comparison with twisted pair
– Higher bandwidth– Supports faster communication speeds– Supports multi-drop connection
CoaxialCable
Multi-drop
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Limiting Factors on Communication Speed
Communication SpeedBandwidth Technology
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Continuation of Bandwidth and Technology on
Communication Speed• Bandwidth limitation
– Use better technology such as data compression used in modems to increase speed of communication
• Bandwidth and technology limitation– Move to higher bandwidth media such
as fiber cables
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Speed Dependency on Bandwidth and
Technology
Medium 1
Technology Medium 2
Higher Bandwidth
Medium 1 example can be shielded twisted pair and medium 2 example can be fiber.
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END OF MODULEEND OF MODULE
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MODULE
An Overview of Digital Technology
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Areas of Application
• Computers• New telephone networks• Phased introduction into television
broadcasting
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Digital Technology
• Basis– Digital signals that could be assigned
digital values
• Digital computer technology– Digital signals – Binary representation
• Encoded into ones and zeros
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Processing using computer technology Programmable services Better quality due to being able to
reconstruct exact digital patterns at the receiving end
Faster communication speeds are possible
Digital Advantage
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Digital Signal
1 0 1 1 0 1 0 0
Pulse
Time
Sig
nal
Str
eng
th
Pulse Duration
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Clock Speed and Pulse Duration
PulseDuration
MHz
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Clock Speed and Execution Speed
• Pulse duration is inversely proportional to the clock frequency
• Faster the clock speed, the smaller the pulse duration
• Smaller the pulse duration, the faster the execution in general
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Clock Speed and Communication Speed
• Faster the clock speed, smaller the pulse duration
• Smaller the pulse duration, smaller the time taken to transmit one bit of information
• Therefore, faster the clock speed measured in MHz, faster the communication speed measured in Mbps in general
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END OF MODULEEND OF MODULE
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MODULE
Digital-to-Analog and Analog-to-Digital Interfaces
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The Need for Conversion
• Analog-to-Digital – Connection of a computer to an
analog communication line
• Digital-to-Digital – Connection of a computer to a digital
ISDN line
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Digital-to-Analog Interface
Comp.Sys. 1
Comp.Sys. 2Modem Modem
DigitalSerialRS-232C
DigitalSerialRS-232C
AnalogITU V.90
POTS
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Digital-to-Digital InterfaceA
Comp.Sys. 1
Comp.Sys. 2
ISDNAdapter
ISDNAdapter
DigitalSerialRS-232C
DigitalSerialRS-232C
Digital ISDN
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END OF MODULEEND OF MODULE
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MODULE
Overview of Digitization Of Information
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Module Objectives
• Define the representations of information
• Explain the need to digitize• State the advantages of
digitization
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Digital Information Processing
Data
Audio
Image
Video
Digitized and Encoded
DigitalTransmission
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The Need to Digitize
• Essential for computer processing• Essential for transmission
– Entry point to networks is a often a computer
– An increasing number of communication lines are digital lines
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The Advantages of Digitization
• Information could be processed by the computer
• Easy transmission of information• Minimize loss of quality during
transmission
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END OF MODULEEND OF MODULE
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MODULE
Digitization Of Data
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Codes Used in the Digitization Of Data
• Coding Standards– ASCII – EBCDIC– Unicode
• ASCII Code example– A=1000001
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The Unicode
• Replace the ASCII coding system in microcomputers
• All variations of the Latin language– English– European languages
• Chinese and Japanese• 18 Major languages
– Eg: Tamil
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Unicode Possibilities
• It is a 16-bit code as opposed to the ASCII code that is basically an 8-bit code
• It is therefore possible to have 65,536 variations in UNICODE
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Communication With ASCII And EBCDIC
• Latin languages can be transmitted in coded form
• Other languages– Bit-mapped image transmission– Requires considerably more bandwidth– An exception is the use of true-type
fonts to display the characters of a language not supported by ASCII
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Communication With Unicode
• Binary encoded transmission– Latin languages– 18 major languages– Chinese, Japanese etc.
• Transmission itself requires less bandwidth
• Universal usability of software in all the supported languages
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Unicode Advantage in WWW Transmissions
Client
TamilWeb Site
Internet Explorer Browser retrievingTamil pages on a client supporting Unicode.
Tamil pages are transmitted in their binary encoded form.
Site created using all the tools such as theMS-IIS.
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Transmission of Tamil Pages as Images on WWW
ClientTamilWeb Site
Internet Explorer Browser retrieving Tamil pages similar to images.
Binary image transmission of Tamil pages.
Web pages scanned andstored as images.
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Using Downloaded Fonts to Host and Transmit
Tamil Pages
ClientTamilWeb Site
Internet Explorer retrieving Tamil pages.
Site createdwith tools such as MS-IIS.
Download and installthe Tamil fonts.
Binary encoded form.
Bandwidth requirements are low.
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END OF MODULEEND OF MODULE
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MODULE
Digitization Of Audio
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Digitization Of Audio: Overview
• Take samples of audio at pre-determined time intervals known as the sampling rate
• Represent the sampled audio with digital signals– Pulse Amplitude Modulation (PAM)
• Encode signals into binary code– Pulse Code Modulation (PCM) that
incorporates PAM as well– Required for computer processing
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Digitization of Audio: Pulse Amplitude Modulation
(PAM)Audio
9 8 7 6 7 9
Digital Signals must further be encoded into binary signals for computer processing and transmission.
Sampling Interval
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Digitization and Encoding of Audio: Pulse Code Modulation (PCM)
• PCM is a two step process• First the audio is sampled and
represented by digital signals• The digital signals are then
encoded in binary form
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Binary Encoding of Signals in Pulse Code Modulation
(PCM)
9 8 7 6 5 6
1001 1000 0111 0110 0101 0110
The integer numbers have effectively been coded into zeros and ones. The ones and zeros now contain the audio information encoded in a form that could be processed by a computer.
PCM
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Salient Points on the Digitization Of Audio
• Sampling rate and the number of bits used for representing the samples will determine the quality of the audio
• Quality is retained in transmission because only codes are transmitted
• Audio can be recreated to the original quality by extracting the pattern from the digital code
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END OF MODULEEND OF MODULE
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Effect of Sampling Frequency
• Higher sampling frequency– Smaller sampling intervals– Frequent sampling– Better quality because the audio
pattern is captured better– Higher bandwidth required for
transmission– Higher disk space required for storage
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END OF MODULEEND OF MODULE
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MODULE
Audio Quality Vs Bandwidth in Audio Transmission
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Module Objectives
• Discuss the two important factors that influence the quality of digitized audio
• Outline the procedure for computing bandwidth requirement based on the factors mentioned above
• Present bandwidth requirements for sample audio formats
• Introduce the concept of audio streaming on the WWW
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Factors Affecting Quality
Number of bits used for binary encoding. Example: 4 bits allow 16 amplitude variations to be represented.
9 8 7 6 7 9
Sampling Interval
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Computation of Bandwidth Requirement for
Transmission• Problem:
– Compute the audio streaming rate for a voice grade circuit given that the number of bits used in the sampling is 8
• Background information– A voice grade circuit has a bandwidth of
approximately 4000 Hz
• General rule– For acceptable quality, the audio must be
sampled at twice the frequency of the voice grade bandwidth
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Problem Representation
79 68 57 46 57 79
1/8000 Secondsor 2X4000 samples per second
8 bits are used enabling 256 amplitudes to represent the human voice which is considered to be adequate.
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Bandwidth Computation
• Number of samples – 8000 per second
• Number of bits per sample– 8
• Bandwidth requirement– 8X8000 bps = 64,000 bps– Approximately 64K bps
• 64K bps is the speed of a single ISDN (B) channel
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Examples in Audio Quality and Bandwidth
Requirement
• CD quality– 44,100 Hz, 16 bit, Stereo– 1376K bps
• Radio quality– 22,050 Hz, 8 bit, mono– 176K bps
• Telephone quality– 11,025 hz, 8bit, mono– 88K bps
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Recording Quality and Bandwidth Requirement
Demonstration
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Recording Used in this Example
• Settings for recording– 11K Hz, 8 bit and mono
• Audio bandwidth requirement is 88K bps
• Streaming is required to send the audio alone over the Internet
• Approximate bandwidth required for both video and audio is 133K bps
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Audio Transmission In WWW
ClientReceive audio usingInternet Explorerand a plug-in to receive the audio stream.
Audio streaming requires compression.
Real-time audiobroadcast supportusing streamingserver module.
28-56K bpsWebSite
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Delivery of Instruction Over the WWW
Client
WebSite
Receive audio/video usingInternet Explorer.
Audio/Video streaming.
Store streamed audio/video using StreamCam.
28-56K bps
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Internet Ramp Bandwidth Computation
WWW
A T1 line operating at approximately 1.354M bpscan support approximately 47 connections in theory.
In practice, 23 connections which is half of 47 can besupported with due consideration given to bandwidth bottlenecks.
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Sampling Considerations In Communications
Sender Receiver
Digital audio transmission
Adjust quality (sampling interval and bitrepresentation) to suit bandwidth availability.
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END OF MODULEEND OF MODULE
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MODULE
Quality Retention In Digital Transmission
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Module Objectives
• The overall purpose is to discuss the retention of audio quality under digital transmission by comparing the same under analog transmission
• Discuss briefly the transmission of audio over the WWW
• Provide a brief introduction to the role played by the Digital Signal Process or DSP in digitizing audio
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Analog Audio Transmission
Audio Priorto Transmission
Audio withInterference
Transmission
Audio After Filtering
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Passage of Analog Audio Over Analog Lines
AnalogAudio
AnalogSignals
AnalogSignals
AnalogAudio
Telephone
Telephone
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Recreation of Audio from Analog Signals
• A difficult task• Complex algorithms are used to
filter noise etc. for better audio transmission
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Signal Passage in Digital Audio Transmission
Encode
TransmitRecreate
Decode
Audio
Audio
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A Sample Digital Audio Transmission Path
AnalogAudio
DigitalAudio
ISDNAdapter
ISDNAdapter
DigitalAudio
AnalogAudio
SoundCard
SoundCard
ISDNLines
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Sound Generation
• Sound is recreated at destination– Using FM synthesis– Using wave table generation
• Noise is not an issue in digital transmission
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Digital Advantage in Audio Transmission
• Only codes are transmitted• Original encoding is recreated• Original audio is reproduced• Again, sampling rate and number
of bits used in each sample determine the quality
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Digitized Signal Passage Over Analog Lines
Encode
TransmitRecreate
Decode
Audio
Audio
Limited Sampling
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A Sample Digital Audio Transmission Path
AnalogAudio
DigitalAudio
Modem
Modem
DigitalAudio
AnalogAudio
SoundCard
SoundCard
AnalogPSN
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Audio Transmission In WWW
Client
WebSite
Receive audio usingInternet Explorerand RealAudio plug-in.
Audio stream over analog/digital line.
Real-time audiobroadcast supportusing RealAudiostreaming server module.
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Digital Signal Processor
DSP
Digital Analog
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END OF MODULEEND OF MODULE
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MODULE
Digitization Of Image
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Module Objectives
• Give an overview of the process of digitizing an image– Black and white, gray scales, color
• Compute sample storage and bandwidth requirement for images with the following characteristics– Black and white, 16 gray scales and color
• Discuss the factors influencing bandwidth requirement in image transmission
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Digitization Of Image: Overview
PixelHorizontal Resolution
Vert
ical R
eso
luti
on
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Digitization of the Letter L
Number of bitsdetermine the amount of information that couldbe stored.
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Digitization Of Image: The Process
• Divide the image into a grid of pixels that may be considered as the sampling points of the image
• Digitize information on each pixel• Store and transmit
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Resolution
• Horizontal resolution– Number of horizontal pixels
• Vertical resolution– Number of vertical pixels
• Image resolution– Horizontal by vertical resolution– Ex: 640 by 480
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Digitization of Black and White Image
• White– A pixel lit represents a 1
• Black– A pixel not lit represents a 0
• Storage required per pixel– 1 bit
• Storage required for 640 by 480 resolution image– 640 times 480 bits = 307,200 bits = 38.4K Bytes
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Digitization of Image Using Gray Scales
• A pixel may take a value between 0 and 15 for 16 gray scales
• A gray scale of 3 can be coded as 0011 and the others similarly using this 4 digit code
• The bandwidth requirement for the transmission of a 640X480 image in this case is as follows:– 640X480X4 = 153.5K Bytes
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Digitization of Color Image
• Image coding – Each pixel may take a value between o and
255 if 256 colors are to be represented
• Storage requirement– Digitizing of images requires substantial
number of bytes and hence large storage space for processing
• Bandwidth requirement– Higher bandwidths are required to transmit
color images
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Bandwidth Computation for Image with 256 Colors
• Resolution is 640X480• 8 bits are required to represent
256 colors• bandwidth requirement for the
transmission of one image is as follows:– 640X480X8 = 307.2K Bytes
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The Effect of Color Depth and Resolution
• Compare VGA and SVGA– SVGA provides higher resolution
• Practical implication– More colors less resolution– 256 colors at lower resolution– 16 colors at higher resolution
• Rule– Higher the resolution the lower the
number of colors available
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Factors Affecting Bandwidth Requirement in
Image Transmission
• The higher the resolution, the higher the bandwidth required
• The higher the color representation, also known as color depth, higher the bandwidth requirement
• For true color, 24 bits are required to represent each pixel
• The file sizes in raw image capture can thus become very large
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END OF MODULEEND OF MODULE
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MODULE
Compression of Digitized Images
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Module Objectives
• Briefly outline the factors conducive to the compression of images
• List a few image compression formats• Explain image compression using a
simple example• Discussion the implication of
transferring image files over a modem connection
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Compression of Digitized Images
• Compression is required to reduce the size of the image file
• Large blocks of unchanged data in an image (background) offers an opportunity to compress the image
• Image files are almost always compressed
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A Few Compression Formats
• GIF• JPEG• MIC (Microsoft Image Composer)• PCD (KODAK) - Used by Corel
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Image File Format Extensions
• File formats often represent the compression procedure being used
• Examples:– tiff– pcd– gif– pcx– bmp
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Loss-less Compression and Others
• Some compression formats offer loss-free compression of the image
• Others sacrifice minimal loss for the sake of reduced storage and bandwidth requirements
• Fortunately, the loss is not easily detected by the naked eye
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Image Transmission Considerations
Sender Receiver
Adjust image to suit available bandwidth.
Adjustable features are as follows.- Resolution- Color depthAdjusting the size also reduces the bandwidthrequirement because of a corresponding reductionin the number of pixels required to representthe image.
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A Peek At Data Compression
• 0 0 0 0 0 0 0 0 0 0 0 - - - - - -0 1 1 1 1 1 11 …... 0
• THE ABOVE CAN BE COMPRESSED INTO = #9000$0#– 9000 bits are compressed into 8
characters that require approximately 64 bits for transmission
– 9000 ZEROS ARE CODED INTO #900$0#
#600$1#
INTERPRET WITHIN THE # SIGN
600
NUMBER COUNT1
CHARACTER BEINGTRANSMITTED
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Modem Implication in Image Transmission
• Modems also compress the data stream to achieve higher transmission speeds
• Because of the fact that the images are already compressed, the full speed benefit may not be realized when images are transmitted over a modem connection
• An already compressed image file does not, for instance, offer itself well to further compression in the modem
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END OF MODULEEND OF MODULE
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MODULE
Digitization Of Video
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Module Objectives
• Present the digitization of video as an extension of the digitization of image
• Give an overview of video transmission in video conferencing
• Discuss the various analog and digital lines that could be used for video conferencing
• List a few commercially available video conferencing products
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Digitization Of Video
• Digitization of video is an extension of the process of digitizing image
• 30 frames of images per second, in general, defines continuos motion
• In communications, 25 frames per second is considered to be continuous motion
• 15 frames per second is currently used in video conferencing over digital lines for acceptable reception of video
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Computation of Bandwidth for Raw Transmission of
Video
• Image resolution is 640X480• Number of colors is 256 (8 bit)• Acceptable reception requires 15
frames per second• Therefore, the bandwidth for the
raw transmission is as follows:– 640X480X8X15 = 36.86M bps = 4.6M
Bps
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Compression Standards Used in the Digitization of
Video• MPEG 1 and MPEG 2• Indio• Video for Windows• QuickTime• ActiveMovie• AVI
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Streaming Formats for Video
• Various streaming formats are supported by different vendors– RealVideo
• Microsoft’s streaming format– Active Streaming Format (ASF)
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Overview of Video Transmission in Video
Conferencing• Acceptable speed
– 15 frames per second
• Transmission techniques– Data compression– Only changes to the frame are
transmitted
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The Effect of Size of Window on Video
Conferencing • Minimize for maximum efficiency• Transmit less number of pixels in
minimized form
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Communication Links for Video Conferencing
• Possible on analog lines using 28,800 bps transmission speed but not desirable
• Digital lines are preferred and the guidelines are as follows:– Possible at 128k bps using ISDN lines– Acceptable at 384k bps – 1M bps and above offer good quality
video transmission
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Video Conferencing Products
• Intel ProShare• CU-See Me• Picturetel• C-phone• etc.
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END OF MODULE END OF MODULE
END OF CHAPTER END OF CHAPTER