Multimedia is a program that combines: a. Text b. Graphics c. Animations d. Audio e. Video.
1 Chapter 1: Overview 2 What is multimedia? Multimedia is when you have too many cables. ...
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Transcript of 1 Chapter 1: Overview 2 What is multimedia? Multimedia is when you have too many cables. ...
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Chapter 1: Overview
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What is multimedia?
Multimedia is when you have too many cables. Multimedia combines audio and visual materials to
provide computerized interaction of text, sound, graphics, images, animation & video to enhance communication and to enrich its presentation.
Multimedia systems handle at least one type of “continuous media” as well as “static media”.
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Multimedia applications
Videodisc applications A laser disc (LD) can store about 1 hour of video (per
side), or 100,000 video frames. A DVD can hold 2-8 hrs of high-quality video
Electronic games Each game is a highly interactive multimedia application
that presents layered-2D/3D animation with synchronized sound effects and music.
New generation of computer games usually use optical disks (CD/DVD/GD-ROM) to store game data.
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Multimedia applications
Web browsers A hyper-document is a document composed of
multiple media types. Multimedia presentation systems
An “engine” that displays, synchronizes, provides interaction with, and generally manipulates multimedia material (e.g., Macromedia Director).
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Multimedia applications
Multimedia mail systems Handle electronic messages containing audio, graphics, and other
media. 3 components: Composition, Transmission, Presentation.
Teleconferencing A computer equipped with microphone, speakers, and a video
camera, and placed on a multimedia network, can establish audio and video connections between other, similarly equipped, machines.
Multi-user tools, such as group editors. A group editor allows conference participants to share documents, and to edit the documents simultaneously.
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Multimedia applications
Multimedia services Interactive TV Interactive shopping Education Medical services (telemedicine) Video-on-demand
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Analog vs. Digital
Two ways to process information: analog and digital
Examples: LP vs. CD radio vs. web-radio slide-rule vs. calculator
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Analog recording
Sound is caused by a variation of air pressure – a sound wave
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Analog recording
An audio tape records an analog signal that represents the sound wave.
An analog signal is continuous – there are an infinite number of points (values) and each value has an infinite precision.
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Digital recording
To record an analog signal by a computer, we need to perform analog-to-digital conversion (ADC): Sampling Quantization Coding
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ADC
Consider an analog signal
time
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Sampling
convert continuous signal into discrete values by taking samples
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Sampling
The original signal can be approximated by interpolation using the sampled values.
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Sampling
More samples more accurate approximation
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Quantization
A computer cannot record the values with infinite precision. A value has to be quantized.
a quantizationlevel
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Quantization
A computer cannot record the values with infinite precision. A value has to be quantized.
a coarserquantization
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Quantization
Each value is replaced by the nominal value of its quantization level.
a sample value
a nominalvalue
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Quantization
Each value is replaced by the nominal value of its quantization level.
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Quantization
The difference between a sample value and its quantization value is called the quantization error.
quantization error
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Quantization
More quantization levels gives a more accurate representation.
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Quantization
More quantization levels gives a more accurate representation.
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Quantization
More quantization levels gives a more accurate representation.
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Quantization
Note that quantization does not necessarily have to be uniform or linear.
widerquantizationlevel
narrowerquantizationlevel
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Coding
assign a codeword to each quantization level.
00001000
1101
1001
0101010000110010
0001
101010111100
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Coding
An analog signal could then be represented digitally by a string of 0’s and 1’s 0010 0011 0011 0000 1010 1011 … …
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Why digital?
ADC introduces error the waveform constructed by interpolating samples is not a verbatim
copy of the original quantization introduces quantization error
so … Why digital representation? What should be the sampling frequency? How many quantization levels (or bits/sample) shall we use?
Example: for CD-DA: sampling frequency: 44,100 samples per second 16 bits per sample (i.e., 65,536 quantization levels)
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Why digital?
easy integration & sharing of resources (storage, transmission network).
can be processed by a computer, e.g., encryption, watermarking, compression, digital effects, etc.
more “reliable” storage and transmission (error-correction). can be used and copied many times without losing quality.
channel channel analog signal transmission
channel reconstruct digital signal transmission
original
“blurred”
“pixelated”
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Media types
Non-temporal (Discrete) – do not have a time dimension, and their contents & meanings do not depend on the presentation time. Text Image Graphics
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Media types
Temporal (Continuous, Isochronous) – have a time dimension. They convey meanings only if “displayed” at a specific rate. Video Digital Audio Music
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Text
not visually exciting conveys essential and precise information text representation: e.g., ASCII storage “friendly” sometimes, certain information is too
abstract to be captured by words
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Digital images
To digitize a photo, we again perform ADC
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Digital images
sampling
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Digital images
pick a sample value from each “box” to record
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Digital images
finer sampling gives a clearer image
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Digital images
finer sampling yet
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Digital cameras
A Charge-coupled-device (CCD) camera has a 2-dimensional array of photosites that convert the amount of light intensities into equivalent electrical charges.
Each photosite is covered by a color filter (red, green, or blue).
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Digital cameras
R G BB R GG B R
The amount of charge at each photosite tells the intensity ofa color component of light detected at that point.
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Digital cameras
R G BB R GG B R
red
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Digital cameras
R G BB R GG B R
green
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Digital cameras
R G BB R GG B R
blue
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Digital images
two-dimensional arrays of pixels (picture elements) of varying color and intensity.
color model: how to specify the color of a pixel? RGB: colors can be represented by a numeric triple
specifying red (R), green (G), and blue (B) intensities. YCRCB (for digital images and video) CMY(K) (for printing)
Cyan (no red) Magenta (no green) Yellow (no blue) K — black ink
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Digital images
Compression A page-sized 24-bit color image with 300 pixels per inch
takes up about 20Mbytes. Lossless and lossy compression. Many different standards: JPEG, GIF (Graphic
Interchange Format), ...Example: run-length encoding.
Image transformation and processing. E.g., morphing (one image transforms into another).
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Graphics data are represented by a geometric model + a set of graphics operations.
Geometric model A collection of 2D/3D geometric primitives
(lines, circles, polygons, curves). Transformations: rotation, translation, scaling.
Graphics
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Graphics
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3D models
taken fromPlanetArchitecture
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Graphics operations Coloring, shading, lighting, and viewing.
ambient light (from all directions)point light (inverse square law)spot light (a cone-shaped volume)
Graphics
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Graphics
Texture mapping (applying an image onto a surface)
Renderingconverts a model + shading, lighting + viewing ... into
an image.
Animation Eye-catching Good for demonstration
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Graphics
taken fromACM ComputerGraphics ‘97
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Graphics
taken fromPlanetArchitecture
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Analog video
A sequence of images called frames, “persistence of vision”.
Originally, motion pictures are shown at an (insufficient) frame rate of 16fps.
It was found that for smooth motion, 24fps is needed.
Attributes: frame rate, resolution, aspect ratio, interlacing, refresh rate
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Analog video
Formats. e.g., NTSC (National Television Systems Committee) PAL (Phase Alternation Line).
format frame rate scan lines aspect ratioNTSC 30 525 4:3PAL 25 625 4:3HDTV(US) 30 1125 16:9HDTV(EURO) 25 1250 16:9
MUSE(Japan) 30 1125 16:9
picturewidth topictureheight
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Analog video
Theoretically, most color can be produced by mixing 3 primary colors (red, green, blue). An analog video camera produces 3 distinct continuous signals, one for each color component.
black
white
horizontalblanking
scan linesignal
white
black…
vertical blanking
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Analog video
A video signal is applied to a TV (a CRT) to control the power of an electron beam that strikes on the phosphors on the inside of the CRT surface.
With the 625/50 system (PAL), for example, a frame is displayed every 1/25 seconds.
Unfortunately, the phosphors do not stay lit that long flickering
To prevent flicker, the picture has to be refreshed at least 50 times per second.
Interlacing: a frame is divided into 2 fields: odd-lines and even-lines, a field is displayed every 1/50 seconds.
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Analog video
time0 1/25
frame 1 frame 2
1/50
progressive
interlaced
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Analog video
Luminance/chrominance principle: the three primary colors can be converted into 2 parts: Luminance: information on the lightness of the image. Chrominance: information on the color of the image.
Because the human eye is not very sensitive to color information, the bandwidth of these 2 color components is reduced before transmission.
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Analog video
Video storage video tape e.g., VHS tape
about 240 scan lines resolution problem: loss of quality when copying and repeated
playback due to stretches and magnetic material wearing off.
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Digital video
A video can also be represented by a sequence of digital images.
broadcast quality video (uncompressed): 1 sec > 20 MB
For lesser quality, and a good compression technique, it is possible to achieve:
1 sec = 1.2 Mb transfer rate of (single-speed) CD-ROM VCD
Data rate of a DVD movie is about 2GB/hr. Compression: lossless and lossy.
B – byteb – bit
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Digital video
For lossy compression, we can achieve a 50:1 or higher compression ratio.
MPEG: The Moving Pictures Expert Group MPEG-1: 1.5Mbps VHS quality video MPEG-2: 4-10 Mbps (digital TV) MPEG-4: a system which allows a scene structure to be
composed of multiple different objects (video, audio, natural, synthetic)
MPEG-7: multimedia information retrieval
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Digital video formats
CCIR 601(4:2:2 chromatic subsampling) for video exchange 525/60 system: 720 x 480 (take 720 samples from each active scan
line) 625/50 system: 720 x 576
4:2:0 for video broadcast
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Digital video formats
SIF for storage 525/60 system: 360 x 240 625/50 system: 360 x 288 4:1:1 chromatic subsampling
CIF for video conferencing 360 x 288 at 30 fps using 4:1:1 chromatic subsampling
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Digital audio
Digital audio representation produced by sampling a continuous signal generated by a
sound source a process called analog-to-digital conversion (ADC)
Sampling frequency Human ear is sensitive to frequencies of up to about 20kHz
(c.f., rat: 1k – 10k Hz; cat: 100 – 60k Hz) Sampling frequency > 40kHz
audio-CD 44.1kHz, 16 bits per sample ( 96dB max. SNR) DVD audio 196kHz (max), 24 bits per sample (max) (Q: what is the throughput requirement?)
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Digital audio
Number of channels 2 for stereo some audio editing equipment may have 16 or 32
channels Storage
An hour of high quality stereo digital audio requires > 500MBytes of storage.
A CD-ROM can store about 650MBytes of data. A CD-DA can store about 74 minutes of audio data.
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Music
MIDI -- Musical Instrument Digital Interface Digital musical instruments send MIDI messages to a
sequencer. The sequencer composes the music according to the
messages received. The sequencer/synthesizer has a “palette” of sounds for
each type of instrument
MIDI sequencer
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Challenges
Multimedia stresses all components of a computer system (data volume & time constraints)
CPU processing power fast speed for data capturing, CODEC, data enhancement large amounts of data being processed in real-time
Storage and Memory high capacity, fast access time, high transfer rates
System architecture high bus bandwidth, efficient I/O
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Challenges
Software tools for retrieval and data management of continuous
media data
Operating systems support for new data types, real-time scheduling,
multimedia file systems, time-critical synchronization
Networks high bandwidth, low latency, low jitter
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Research areas
1. fast processors
2. high-speed networks
3. large capacity storage devices
4. video & audio compression algorithms
5. graphics systems
6. human-computer interfaces
7. real-time operating systems
8. information storage and retrieval
9. hypertext & hypermedia
10. languages for scripting
11. parallel processing methods
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Compression
Throughput and storage “If a picture is worth a thousand words, then a video is worth
414 million (4-byte) words per minute,” Benny said.(or 25GBytes/hr !!!!)
What are the requirements on network data transfer rate? On disk I/O?
Compression makes it possible. 50:1 yields 0.5 GB/hr. 200:1 for HDTV. How expensive is the processing? Hardware solution?
Software solution?
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Compression
MM systems require data compression for 3 reasons: the large storage requirements of MM data. relatively slow storage devices that cannot play
MM data in real time network bandwidth that does not allow real-time
video data transmission
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Some compression standardsJPEG Digital
compression andcoding ofcontinuous-tonestill images
JointPhotographicExperts Group
15:1 (full color still-frame applications)
H.261 Videocoder/decoder foraudio-visualservices at p*64Kbps
SpecialistGroup onCoding forVisualTelephony
100:1 to 2000:1 (video-basedtelecommunications)
MPEG Coding of movingpictures andassociated audio
MovingPicturesExperts Group
200:1 Motion-intensiveapplications
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Multimedia networking
Many multimedia applications, such as video mail, video conferencing, and video-on-demand, require the support of a high performance network system.
In these applications, the multimedia objects are stored at a server and played back at the clients’ sites.
Remote retrieval of multimedia objects has stringent time constraints.
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Multimedia networking
Delay: the amount of time it takes to transmit a data unit (e.g., a video frame) from a sender to a receiver.
Jitter: delay variation.
source destination
delay
jitter
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Multimedia networking
Characteristics Data Transfer Multimedia transfer
Data rate Low High
Traffic pattern Bursty Stream-oriented
Reliabilityrequirements
No loss Some loss
Latencyrequirements
None Low, e.g., 20 ms
Mode ofcommunication
Point-to-point Multipoint
Temporalrelationship
None Synchronizedtransmission
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Multimedia information retrieval
To retrieve a text document from the Web, we use keyword search via “Alta Vista”, for example.
To retrieve a record from a relational database, such as Oracle, we use an SQL statement.
How shall we formulate a query to retrieve pictures?
What about audio? How do we describe a sound? How do we describe a song?
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Multimedia software tools
Music sequencing Cakewalk
supports general MIDIprovides several editing views (staff, piano roll, event
list) and Virtual Piano
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Multimedia software tools
Image and video editing Adobe Photoshop
allows layering of images, graphics and text includes many graphics drawing and painting tools sophisticated lighting effects, various image processing filters
Adobe Premiere provides many video and audio tracks, superimposition and
virtual clips supports various transitions, filters and motions for video clips a reasonable desktop video editing tool
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Multimedia software tools
Multimedia authoring Microsoft Power Point
building slide show sequence slides include objects of different media, e.g., sound and video limited animation ability
Macromedia Director, Flash Movie metaphor (cast of bitmapped sprites, scripts, music,
sound, and palettes) Lingo script language allows more control of the presentation
sequence. Control of devices, e.g., VCRs and disk players. ready for building interactivities using buttons, etc.