Transcript HDTV (High Definition Television)

HDTV
(High Definition Television)
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.
Currently...
• Less than 1% of US homes have HDTV
capabilities
• Approximately 11% of stations have digital
broadcasts
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
Multicasting
• By using lower-definition signals, one
channel can be split into several channels
• Extra channels used for:
– information services (datacasting)
– music
– Internet services
HDTV Standards
• 8-VSB (vestigial side band)
– US, Canada, South Korea, Taiwan, Argentina
• DVB-T (digital video broadcastingterrestrial)
– Europe, Australia
– Japan uses a system similar to DVB-T
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
High definition studio video
to
Over-the-air broadcast form
• Two stages of processing needed:
– MPEG-2 encoding
– 8-VSB modulation
MPEG-2 Encoding
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Discrete cosine transform
Run length encoding
Bi-directional motion prediction
Multiplexes compressed video information
together with pre-coded Dolby AC-3 audio
8-VSB
Source: www.broadcast.harris.com/customer-service/8-vsb.html
HDTV Types
• HDTV or Digital-ready TV
• 16:9 aspect ratio (width:height)
• Displays:
– 720-line progressive scan signal OR
– 1080-line interlaced signal
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
Progressive
• Lines of picture transmitted consecutively
one line after another rather than 2
overlapping fields
• Like computer monitor
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
Future of Digital TV
• May 2002: All commercial stations must
begin digital broadcasts
• May 2003: All stations (commercial & noncommercial) must begin digital broadcast
• May 2006: Analog TV signals completely
eliminated