hdtv (high definition television). hdtv history early 1980’s: –japan created analog hdtv...
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HDTV(High Definition Television)
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HDTV History
• Early 1980’s:– Japan created analog HDTV
• Mid-1980s:– US, trying to stay competitive, decided to go
digital– Congress gave stations a separate channel for
transition to digital broadcast with the goal of all stations using digital broadcasts by 2006.
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Currently...
• Less than 1% of US homes have HDTV capabilities
• Approximately 11% of stations have digital broadcasts
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Digital Broadcasts
• Digital TV is not necessarily HDTV
• FCC only mandates transmission of digital television, not HDTV
• Several broadcasters use multicasting instead of transmitting HDTV
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Multicasting
• By using lower-definition signals, one channel can be split into several channels
• Extra channels used for:– information services (datacasting)– music– Internet services
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HDTV Standards
• 8-VSB (vestigial side band)– US, Canada, South Korea, Taiwan, Argentina
• DVB-T (digital video broadcasting-terrestrial)– Europe, Australia– Japan uses a system similar to DVB-T
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HDTV Features
• Provides up to 60 frames/sec screen writing rate
• Uses MPEG-2 data compression– source info data rate is 1.2Gbps– broadcast data rate is 20Mbps
• Square pixels 1/4 the size of analog TV’s pixels
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High definition studio videoto
Over-the-air broadcast form
• Two stages of processing needed:– MPEG-2 encoding– 8-VSB modulation
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MPEG-2 Encoding
• Discrete cosine transform
• Run length encoding
• Bi-directional motion prediction
• Multiplexes compressed video information together with pre-coded Dolby AC-3 audio
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8-VSB
Source: www.broadcast.harris.com/customer-service/8-vsb.html
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HDTV Types
• HDTV or Digital-ready TV
• 16:9 aspect ratio (width:height)
• Displays:– 720-line progressive scan signal OR– 1080-line interlaced signal
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Interlaced
• TV camera captures an image of 480 lines every 1/60th of a second
• Allocated broadcast spectrum isn’t wide enough, so signal is compressed by discarding 1/2 of the lines
• Transmits at 30 frames/sec with 2 fields/frame
• Fields alternate every other resolution line
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Progressive
• Lines of picture transmitted consecutively one line after another rather than 2 overlapping fields
• Like computer monitor
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Digital Cable
• Conventional cable broadcasts analog signal
• Digital cable broadcasts digital signal to provide higher quality picture/sound
• Digital cable is incompatible with digital signal used for HDTV
• HDTV signal received through satellite dish, conventional cable, or antenna
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Future of Digital TV
• May 2002: All commercial stations must begin digital broadcasts
• May 2003: All stations (commercial & non-commercial) must begin digital broadcast
• May 2006: Analog TV signals completely eliminated