Multimedia Information
Representation
1
Analog Signals
Analog signal and Signal bandwidth and
frequency components effect of bandlimiting channel
❖ Fourier transform and analysis
2
Signal encoder design
Associated wave form
Signal encoder
❖ Nyquist sampling theorem
In order to obtain an accurate representation of a time-varying analog
signal, sampling rate >= 2 x highest sinusoidal frequency component
⬥ Nyquist rate
3
Bandlimiting Filter
❑ Undersampling (<
Nyquist rate) results in
additional FC being
generated that are not
present in the original
signal
Cause the original signal
to become distorted
Need bandlimiting
(antialiasing) filter
4
Quantization Intervals
Source of errors Quantization Interval
q = 2Vmax / 2n
Dynamic range of signal
D = 20 log10(Vmax/Vmin) dB
Noise polarity
5
Decoder Design
6
Text
❑ Unformatted text: plain text
ASCII character set
Mosaic character set used in Videotex and Teletext
❑ Formatted text: richtext
❑ Hypertext
Pages and hyperlinks
HTML, SGML
7
Images: Graphics
❑ Graphics: computer-generated images
❑ Representation of a computer graphics
High-level version: e.g) PostScript
Bit-map format: GIF, TIFF
8
Images: Digitized Documents
9
Images: Digitized Pictures
❑ Color principles
Additive color mixing
Subtractive color mixing
10
Raster-scan principles
11
Raster-scan Display Architecture
❑ Pixel depth: # of bits per pixel
❑ CLUT (color look-up table)
12
Screen Resolution
Visible lines per frame
Digitization spatial resolution
13
Digital Cameras and Scanners
Color image capture
RGB signal generation alternatives
14
Audio
❑ Speech signals: 50Hz ~ 10kHz
Nyquist rate = 20ksps
❑ Music-quality audio: 15Hz ~ 20kHz
Nyquist rate = 40ksps
15
PCM Speech
Signal encoding and decoding
Compressor
Expander
µ-law : North America, Japan
Obtain 12-bit performance!!
A-law: Europe and others 16
CD-quality Audio
❑ CD-DA (Digital Audio)
standard
Sampling rate: 44.1 ksps
16 bits/sample
Bit rate for stereo music
⬥ 2 channel x 44.1 ksps x 16
bits = 1.411 Mbps
17
Synthesized audio
❑ MIDI (Music Instruments
Digital Interface)
A MIDI message = (status
byte, data bytes, … )
Music: sequece of
message
Play out by the sequencer
program or saved in a file
Need sound card
18
Compact Disks (1)
❑ CD-DA: Digital Audio (1980)
Access rate: 150 Kbps, sampling rate: 44.1 KHz,
storage: 682 MB
❑ CD-ROM (1985)
To store mixed text, data, video and audio
Access rate: 150 Kbps(1X) ~ 24 x 150 Kbps (24X)
❑ CD-I: Interactive (1986)
For real-time playback of multimedia and interactive
games
Stores mixed text, graphics, video and audio for
high-speed information retrieval
Handles synchronization among interleaved data,
compressed audio, still frames and full-motion video
files
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Compact Disks (2)
❑ DVI: Digital Video Interactive/Initiative (1986)
Use Indevo (Intel Video) – a proprietary compression
method
Non real-time compression, real-time decompression
❑ CD-XA: Extended Architecture (1989)
Improves CD-ROM’s video and audio capability
Contains mixed text and data with audio and video
(similar to CD-I)
Compliant to CD-ROM, CD-I
❑ PhotoCD
Store max. 100 compressed photos
Uses same format as CD-XA
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Compact Disks (3)
❑ Video CD (1993)
Full-motion video (MPEG-1)
Stores 74 minutes of video
❑ CD-R: Recordable (1990)
Permits appending information to the previously
recorded information
❖ MPC Level 3 specifies that the CD-ROM must
read CD-DA, CD-ROM, CD-XA, CD-I, Video CD,
CD-R, Photo CD, CD Extra.
21
Compact Disks (4)
❑ DVD: Digital Versatole Disk
Larger storage space: 682MB 4.7 ~ 17 GB
⬥ Shorter pit length: 0.834 0.4 micron
⬥ Tighter track spacing: 1.6 0.74 micron
⬥ Shorter wavelength laser: 780nm 635 ~ 650 nm
Store anything a CD is capable of holding
⬥ Even MPEG-2 and Dolby AC-3
22
Video Applications
❑ Entertainment
Broadcast TV, VCR/DVD recording
❑ Interpersonal
Video telephony, videoconferencing
❑ Interactive
Windows containing short video clips
23
Interlaced Scanning
24
TV broadcast: Color Signals
❑ Requirements
Color TV broadcast should be used by an existing
monochrome (back-and-white) TV set
Color TV should be able to produce black-and-white
pictures from monochrome broadcast
❑ Properties of a color source
Brightness: amount of energy that stimulates the eye
⬥ Varies on a grayscale from black through to white (highest)
⬥ Independent of the color of the source
Hue(색조): actual color of the source
⬥ Each color has a different frequency/wavelength
Saturation(채도): strength or vividness of the color
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Luminance and Chrominance
❑ Luminance: related to the brightness
Amount of white light
Same as the signal used by monochrome TV
Ys = 0.299Rs + 0.587Gs + 0.114Bs
❑ Chrominance: related to the hue and saturation
Color difference signals i.e no brightness info.
⬥ Cb = Bs – Ys, Cr = Rs – Ys
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Composite video signal
❑ Magnitude of the two color differences are both
scaled down
If the two color difference signals are transmitted,
amplitude of luminance signal can become greater than
that of the equivalent monochrome signal
❑ PAL
Y = 0.229R + 0.587G + 0.114B
U = 0.493(B-Y)
V = 0.877(R-Y)
❑ NTSC
Y = 0.229R + 0.587G + 0.114B
I = 0.74(R-Y) – 0.27(B-Y)
Q = 0.48 (R-Y) + 0.41(B-Y)
27
Signal Bandwidth
NTSC
PAL
28
TV Broadcast
29
TV
❑ Analog TV
Frame rate: # of frames per second produced by a
video signal
⬥ common rate: 25 - 75Hz
Number of scan lines per frame
scan rate: # of lines scanned per second
= frame rate x # of scan lines
Interlacing: to reduce the flickering
⬥ odd field, even field
Aspect ratio: width : height
❑ Digital TV
convert analog signal to digital signal
sampling, quantization, coding
30
Standard Analog TV Systems
Standard Frame rates Scan lines Aspect ratio Interlacing
NTSC 29.97 525(480) 4:3 2:1
PAL 25 625(576) 4:3 2:1
SECAM 25 625(576) 4:3 2:1
31
Digital Video (I)
❑ 4:2:2 format
Studio-Quality TV: ITU-R 601
Bandwidth 6MHz
sampling rate: 13.5MHz
720 samples / line
Bit rate = 216Mbps (PAL,
NTSC)
Subsampling 4:2:2
32
Digital Video (II)
❑ 4:2:0 format
Bit rate = 162Mpbs
❑ HDTV format
16/9 aspect ratio: 1920 x 1152 pixel
Refresh rate: 25Hz / 30Hz
Studio application: 4:2:2 format
Broadcast application: 4:2:0 format
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Digital Video (III)
❑ SIF (source intermediate format)
VCR quality
Used in MPEG-1
½ resolution in both horizontal
and vertical directions (by
subsampling): 4:1:1 format
½ refresh rate (temporal
resolution)
Bit rate: 81Mbps
❑ CIF (common intermediate format)
Videoconferencing quality
Used in H.261
4:1:1 format
Y = 360 x 288, Cb = Cr = 180 x
144
30Hz
❑ QCIF (quarter CIF)
Video Phone Quality
Used in H.261 34
PC Video
Digitization Spatial resolution Temporal
System
Format Y Cb = Cr resolution
4:2:0 525-line 640 x 480 320 x 240 60Hz
625-line 768 x 576 384 x 288 50Hz
SIF 525-line 320 x 240 160 x 240 30Hz
625-line 384 x 288 192 x 144 25Hz
CIF 384 x 288 192 x 144 30Hz
QCIF 192 x 144 96 x 72 15/7.5 Hz
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