index for multimedia technology development process multimedia software calculating graphic file...
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Index for Multimedia Technology
Development Process
Multimedia Software
Calculating Graphic File Sizes
Types of Graphic File
Streaming
Digitised Pictures
Codecs
Digitised Sound
Calculating Sound File Sizes
Synthesised Sound
Digitised Video
Calculating Video File Size
Connecting to Peripherals
File Compression
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Development Process
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Analysis
Design
Implementation
Testing
Documentation
Evaluation
Maintenance
Work out what needs doing. End result is Requirements Specification & Technical Specification.
Storyboarding – shows content, layout and navigation links for the Multimedia application.
Use of Multimedia authoring and Web Page Authoring packages to implement the storyboard designs.
Check all hyperlinks to ensure navigation works, also that layout is correct and that final product works as expected from remote site (web pages)
User Guide (for specialist Multimedia if required) and Technical Guide showing hyperlink relationships, specifying minimum transfer rates.
Evaluate the final product against the initial Requirements and Technical specifications.
Adapting / modifying the Multimedia application to suit changing client needs and emerging technologies.
Multimedia Software – Web Page Creation Software
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Presentations
Sound Editing
Text Editors
Examples: Notepad & Wordpad
Allows the programmer direct access to the html code to add extra functionality i.e. via java script.
Need to know what you are doing. Difficult to judge complex layouts this way!
Used by professional web designers!
WYSIWYG: What you see is what you get
Example: Dream Weaver
Allows user to layout pages like a word processing / desk top publishing application.
Quick results, but limited functionality without ability to access the html code direct.
Ideal for non professionals!C
Normal to use both: WYSIWYG for initial layout – Text Editor to add extra functionality
Authoring software to create multimedia applications: Examples – Director (mainly script based,
have more control over effects), Hyperstudio (mainly icon based, simple to use)
Web Page Development Software
Video Editing
Multimedia Software – Video Editing Software
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Timeline View
Examples: Camtasia Studio, Movie Maker
Allows user to click & drag video, sound and graphics and adjust the length (time) played in the final presentation.
Can also add Title Clips and callouts.
Storyboard View
Example: Camtasia Studio, Movie Maker
Shows individual clips in sequence allowing the addition of transitional effects between clips such as fade out, fade in etc.
Also allows user to add effects to clips such as making black / white, aged etc.
Video Editing Software
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Presentations
Sound Editing
Web Page Editing
Multimedia Software – Sound Editing Software
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Over amplification has caused clipping (flattening) of sound waves at upper & lower bounds!
Sound Editing
Example: Audacity
• Open files (Stereo 2 channels, Mono 1 channel)
• Highlight areas to delete (cut) unwanted bits
• Adjust ends with Fade In / Fade Out
• Add effects to sounds
• Can copy and paste sounds together to produce mixed track
• If Over amplified will cause “Clipping” and will distort sound badly!
• Can save final track as CD, MP3, Wav etc.
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Presentations
Web Page Editing
Video Editing
Multimedia Software – Presentation Software
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Presentation Software
Example: Microsoft PowerPoint
• Presentations consist of a series of slides
• Slides can incorporate Multimedia elements, such as text,
graphics, sound and video.
• Elements and slide transitions can have animation effects
added.
• You can also add hyperlinks to produce complex
navigational structure giving multiple pathways
• Most modern Presentation packages also give the facility to
save presentations directly into web ready formats.
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Web Page Editing
Sound Editing
Video Editing
Streaming
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This technique enables users to access large multimedia files, such as audio and video, quickly by allowing them to play the file before all of the data has arrived.
Play rate needs to be slower than the transfer rate to operate smoothly!
Streaming follows several steps:
1. Data to be streamed is “Compressed”
2. Server sends data as a series of packets
3. As data packets arrive computer decompresses / decodes and sends to a buffer
4. Data then sent to sound / video card and processed using DSP and DAC
5. Software downloads a few seconds of data into buffer before playing
6. If contents of buffer used before next part of stream arrives then get pauses / missed sections
Types of Streaming:
Live Streaming: Stream data as it is generated. Takes a lot of processing due to need to compress in real time.
Almost Live Streaming: Stream with built in delays to allow for compression process.
File Streaming: Transmitting a file that has already been compressed
Pseudo-streaming: Same as file streaming, but allows user to view after first portion of data is received i.e. 15% (Examples Google video, You Tube)
Embedded Files: Multimedia embedded directly into html and saved with it. Becomes part of the page.
Codecs
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Codec - Compression / Decompression
Codecs are used to compress binary data to reduce file sizes to enable faster transmission over networks / reduce amount of backing storage required to store the data.
Most codecs use algorithms to compress / decompress the files. Audio and Video applications are also used (such as Dix X avi video codec. Can get a full movie down to around 700 Mb)
You cannot use any codec file in every application. For instance PowerPoint will not recognise DivX video, but will recognise .wmv and some other standard avi codecs.
Container Files
A container file can hold several compressed files. When the container file is transmitted a program is needed at the receiving end to regenerate the separate files held within it.
A Zip file is an example of a container file (WinZip uses the LZW algorithm to get lossless data compression)
Digitised Pictures - Hardware
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Scanners & Cameras
1. Light reflected onto row of photo sensitive CCDs (Charged Couple Device)
(Note: one row for black / white, three rows for colour R,G,B, array of CCD for cameras, Video cameras use 3 CCD arrays and a beam splitter to split light into RGB components)
2. Each CCD produces a different voltage depending on the amount of light detected
3. ADC (Analogue to Digital Conversion) takes place
4. DSP (Digital Signal Processor) streams out digital values to backing storage
(may apply compression such as jpeg in digital cameras, mpeg to videos)
Cameras store files onto solid state devices (memory cards), where as Video Cameras tend to store onto Magnetic Tape, DVD discs or built in Hard Drives.
Hardware
CLUT (Colour Look Up Table): used by graphics applications to allow user to specify subset of colours to be used
Calculating Graphic File Sizes
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You will need to be able to calculate file sizes for bitmap graphics using the relationship
File Size = (height in pixels x Width in pixels) x Colour Depth
Example:
Given a 10” x 8” true colour graphic scanned at 600 dpi calculate the file size
Step 1: True colour uses 24 bits (3 bytes) per pixel
Step 2: Height in pixels = 10 x 600 = 6000
Step 3: Width in pixels = 8 x 600 = 4800
Step 4: File size in bytes = 6000 x 4800 x 3 = 8,640,000 bytes
Step 5: 8,640,000 / 1024 = 84,375 Kb
Step 6: 84,375 / 1024 = 82.4 Mb
Remember Colour depth can be 8 bits (1 byte) – GIF & PNG 16 bits (2 bytes) 24 bit (3 bytes) – True Colour
Types of Graphic File – Picture Formats
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24 Bit True Colour
Excellent Quality, can be manipulated at pixel level.
Resolution dependant (pixilation) and very large file sizes
GIF (Graphics Interchange Format)
8 bit (1 byte) per pixel therefore only 256 colour palette. Good for cartoons / line drawings with limited colours. Can set transparent backgrounds (single bit transparency), Can be non interlaced (scan in line by line) or Interlaced (Blurred then sharpen). Can be animated. Utilises LZW lossless compression.
JPEG (Joint Photographic Expert Group)
Millions of colours available, favourite format for cameras. Uses complex algorithm to achieve lossy compression (a compression setting of about 60% will result in the optimum balance of quality and filesize,). Very small file sizes. Can be interlaced.
PNG (Portable Network Graphics)
Much like GIF with PNG-8 having 256 colours, supports data streaming, can be interlaced and has transparency feature. PNG-24 has full colour capabilities and holds an alpha value for opacity. Uses lossless compression.
Dithering &Anti-Aliasing
3D Vectors
Types of Graphic File – 3D Vectors
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Dithering &Anti-Aliasing
3D Vector Graphics
As with normal vectors data is recorded as mathematical values for position, line thickness, fill colour etc.
Now also need to record depth, angle of rotation, surface texture and shadow / position of light source.
Some standard formats include:
SVG (Scaleable Vector Graphics)
e.g. Cube{ Width 20, Height 20, Depth 20}
Cylinder {Radius 20, Height 150}
Sphere {Radius 20}
VRML (Virtual Reality Markup Language)
WRL (World Description Language)
You need a plug in for browsers to display them.
Picture Formats
Dithering & Anti-Aliasing
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3D Vectors
Dithering
Dithering is used to create the impression of more colours than the colour palette / bit depth can represent by putting dots of two or more colours close together to create another colour.
Look at the two examples opposite. The first has only black and white dots, but gives the impression of grey scale and the second has gone from the millions of colours available to 24bits down to 8 bits (256 colours), but still looks similar
Anti - Aliasing
Anti – Aliasing is used to “smooth” the edges of images by blending the edges into the background image. Otherwise you end up with a jagged white line around it.
Picture Formats
Digitised Sound – How sound is recorded
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Sound is an ANALOGUE signal recorded as differing voltages that can be at any level at any given time. These voltages cause electro magnets in speakers to vibrate, recreating the sound waves to hit our eardrums.
But computers only understand DIGITAL signals (o or 1, 5v or 0v) so the analogue signals have to be changed into a binary format.
This is done by taking sample values and recording the voltage values as binary numbers over a given time.
The number of bits used to record these values can effect the quality of the recording (8 bits only allows for 256 states, 16 bits allow for 65536 states)
Obviously there is a need for ADC (Analogue to Digital Conversion) to send digitally recorded music to speakers, as well as DAC (Digital to Analogue Conversion) for recording sound via microphones. This is carried out by SOUND CARD hardware. DSP (Digital Signal Processing) is also carried out.
Sound Terminology
How Sound is Recorded
Digitised Sound – Sound Terminology
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Bit Rate: bits per second required to transmit sound (CD 1378 kbps, MP3 384 kbps)
PCM (Pulse Code Modulation): Method of encoding signal by varying the amplitude of pulses.
RIFF (Resource Interchange File Format): file format that can contain bitmap graphics, animation, digital audio and MIDI files. Wav file format is the RIFF format for storing sound data.
ADPCM (Adaptive Delta Pulse Code Modulation): Compressed PCM data. Only stores changes between samples and not samples themselves. Used in WAV format (either 8 or 16 bit depth with sample rates of 11.025 kHz, 22.05 kHz or 44.1 kHz)
Normalisation: Signal levels of different sounds adjusted to average volume
Clipping: Over Amplification causes data loss at peaks / troughs distorting the sound.
Sound Terminology
How Sound isRecorded
Calculating Sound File Sizes
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You will need to be able to calculate sound file sizes using the formula
File Size = Sampling Frequency (Hz) x Time (s) x Depth (bytes) x Channels
(NB: Mono has One Channel Stereo has Two channels)
Example:
Calculate the file size of one minute of Mono sound sampled at 22.05 kHz anda bit depth of 8 bits
Step 1: 22.05 kHz = 22050 Hz
Step 2: 8 bits = 1 byte
Step 3: Mono = 1 channel
Step 4: 1 minute = 60 seconds
File Size = 22050 x 60 x 1 x 1 = 1323000 bytes = 1292 Kb = 1.26 Mb
Synthesised Sound
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MIDI (Musical Instrument Digital Interface)
• Used to digitally record instruments like keyboards, synthesisers and drum machines.
• Holds information on Instrument, pitch, volume, duration and tempo
• You can save messages generated by many instruments in one file
• Produces very small file sizes
• Can be edited with a text editor
• Used for ring tones on older mobile phones.
• Browsers need plug in to play MIDI files
Digitised Video – File Formats
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AVI (Audio Video Interleave)
Limited file size: 2 Gb
Resolution: 320 x 240
Frame rate: 30 frames per second
Original Microsoft product for use in Windows Media player. Now superseded by Windows Media Video (WMV) as this supports Mpeg 4 compression.
MOV
Apple (Mac) QuickTime video format.
Better Quality than standard uncompressed AVI
Smaller file sizes
Now can be used for steaming video with apple QuickTime player, as well as use on mobile devices.
MPG (Motion Picture Experts Group)
MPEG 1(PAL) Resolution: 352 x 288, 25 Fps
MPEG 2(PAL) Resolution 720 x 576 , 25 Fps
MPEG 2(NTCS) Resolution 720 x 480, 30 Fps
MPEG 2 is standard format for DVD storing a 2 hour film into a few Gb. Now have MPEG 4 that is basis of WMV and can be used for recording video for High End TV use and mobile devices
Lossy compression by use of key frames and recording changes in between key frames
DV (Digital Video)
Also mini DV, DVPro and DVCam
Digital formats for use with digital camcorders
Data rates of 25 to 100 Mbps
Compression Ratio of 5:1
Utilises Intraframe Compression
Calculating Video File Size
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You will need to be able to calculate file sizes for videos using the formula
File Size = (height in pixels x Width in pixels) x Colour Depth x Frame Rate (s) x length (s)
Example:
What is the uncompressed file size of a 30 second video recorded at 25 frames per second. The video resolution is 640 x 480 and it was shot in 24 bit true colour.
Step 1: True colour uses 24 bits (3 bytes) per pixel
Step 2: Height in pixels = 480
Step 3: Width in pixels = 640
Step 4: File size in bytes = 480 x 640 x 3 x 25 x 30 = 691200000 bytes
Step 5: 691200000 / 1024 = 675000 Kb
Step 6: 84,375 / 1024 = 659.2 Mb
Techniques to reduce file size:
Reduce Frame Rate (causes flicker below 22)
Reduce Colour Depth (loss of quality)
Reduce Resolution (smaller image)
Crop / Cut image (reduced picture)
Connecting to Peripherals
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USB (Universal Serial Bus)
Link Multiple devices via one port (max 127)
Fast Transfer Rates (USB 1 max 12 Mbps)
(USB 2 max 480 Mbps)
Plug and Play (no reconfiguration required)
Max distance 5 meters
Firewire
Link multiple devices via one port (max 63)
Fast Transfer Rates (800 Mbps – 3.2 Gbps)
Distances up to 100 meters (fibre optic cable)
WiFi
Used to connect LANs (home & office)
Fast Transfer Rates 11 Mbps – 54 Mbps
Max distance 30m
Bluetooth
Wireless connection of mobiles / peripherals
Link Multiple devices via one port (max 8)
Fast Transfer Rates 720 Kbps – 10 Mbps
Can carry digital voice / data transmission
Max distance 10m to 100m (with booster)
Developments inTechnology
MultimediaHardware
Developments in Technology
Sound Card
Needs to carry out ADC / DAC
ADC (Analogue to Digital Conversion)
When converting Analogue input from Microphone into Digital recording of Analogue voltage levels / time as binary values.
DAC (Digital to Analogue Conversion)
When sending Digitally recorded voltage levels to speakers the stored values need to be converted back to an Analogue voltage to make the electromagnets in the speakers vibrate.
Graphics Card
Needs to carry out ADC / DAC / DSP
ADC (Analogue to Digital Conversion)
When converting Analogue input from TV video into digitally stored data about each frame
DAC (Digital to Analogue Conversion)
When transmitting digitally stored values back to a device that only understands Analogue signal. i.e. CRT Monitor, TV etc.
DSP (Digital Signal Processing)
May be required to compress / decompress digital data file and store data in correct sequence. Card may have own processor / RAM
NIC (Network Interface Card)
Provides the physical connection and electronics to connect a computer to a Local Area Network. Converts data into a form that can be transmitted across the network.
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Developments inTechnology
Connecting toPeripherals
Developments in Technology
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Connecting toPeripherals
Holographic Storage
Provides high storage densities of approx. 10 Gb per cubic centimetre and has very fast access time. Like all optical discs it uses lasers to read / write but throughout the whole thickness of the disc in three dimensions.
3D Display Technology
Real 3D display: Old fashioned now with use of Red / blue lenses for pictures / cinema
Virtual 3D display: For use with Virtual Reality systems, goggles or helmet
Flat Panel displays: TFT (Thin Film Transistor) taking over from LCD. Sharper images / colours
3D Flat Panel displays: Three major new technologies
Parallax Illumination – creates two images with same data, each eye recieves different image to create 3d effect.
Beam Splitter Sheet – sits in front of LCD, refracts light to create 3d image
Multiple Layers – uses multiple layers of LCD screens to create 3d effect
Main Uses: Simulators, Research Projects, Image Processing MultimediaHardware
File Compression
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Needed to reduce file sizes for faster transmission over networks and reduce storage requirements
Lossless
Data is encrypted to reduce file size by applying LZW algorithm
Two files created – Dictionary and Data file
Need to transmit both as need dictionary to reassemble data file, but no data lost (get original)
Lossy
Complex algorithms used to reduce file size. Data lost cannot be retrieved
Examples:
JPEG: Cuts out aspects of graphic information that will not be noticed by the human eye. It uses a quality percentage indicator (100 % excellent – 0% grey sludge) and compression rates of 20:1 produces little noticable loss.
MP3: Used on sound files, MP3 achieves compreesion by filtering out aspects of original sound that the human ear will not notice, such as only recording the louder of two sounds. It then uses Huffman Encoding to further compress the file (I min = 1Mb)