Digital Video
•Digital video is essentially a sequence of
digital images
–Processing of digital video has much in common
with digital image processing
•First we review the basic principles of analog
television
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Digital Video - Multimedia - Lecture Slides, Slides of Multimedia Applications
The main points are:Digital Video, Processing of Digital Video, Digital Image Processing, Basic Principles, Analog, Television, Television Fundamentals, Television Cameras, Television Receivers, Create
Typology: Slides
2012/2013
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Digital Video
- Digital video is essentially a sequence of
digital images
- Processing of digital video has much in common with digital image processing
- First we review the basic principles of analog
television
Television Fundamentals
- Color television cameras and television receivers use the RGB (red, green, blue) color system to create any color
- We have seen how raster scan devices operate
- Commercial television systems, however, may use interlaced scanning in addition to the progressive scanning of computer monitors
Television Fundamentals
- Since the phosphors retain their values for longer than the time that it takes to transmit two fields, and since rate of transmission of a field is shorter than the human eye can perceive, the viewer does not perceive this interlacing
- If the frame rate is at least 25-30 frames per second the viewer does not perceive motion in an image sequence as discrete, but as continuous
Interlaced Scanning
- In the figures, the first field is transmitted at
time t = 0 and displayed at time t = f / 2
- f is the frame rate
- The second field is transmitted at time t = f / 2
and displayed at time t = f
- Note that the display at time t = f consists of
information (scan lines) from two distinct
points in time
The second field of a television
transmission
A complete frame
Interlacing
- Interlaced scanning was used in commercial
television systems to decrease the bandwidth
of the transmitted signal and to reduce the
phenomenon known as large area flicker
- These problems had been overcome by the
time bit-mapped computer monitors were
being developed
Deinterlacing
- There are several common
operations that you might want to
perform on interlaced video
- Producing stills
- resizing the video
- changing the frame rate etc.
- Performing these operations on raw,
interlaced, video can produce
undesirable artifacts
Deinterlacing
- Deinterlacing provides a way around
these problems
- All deinterlacing methods involve
turning the field-based image into
a frame-based image by modifying
one of the fields in the image
- Popular methods include duplication
and interpolation
Deinterlacing
- Duplication
- Interpolation
Television Systems
System Scan lines/ frame
Frame rate
Pixels / frame
Bandwidth
NTSC 525 30 /
sec
130,000 4.3 MhZ
PAL 625 25 /
sec
210,000 6 MhZ
SECAM 625 25 /
sec
210,000 6 MhZ
Digital Television
- Considering the bandwidth of the NTSC signal, how does digital transmission compare to analog? We have:
- 30 frames/second x 130,000 pixels/frame x 24 bits/pixel = 93.6 Mbits/second
- To be competitive with analog transmission, a data compression of more than 20:1 is required - All digital television standards therefore include some form of compression.
- The disadvantage of digital television therefore, is the extra bandwidth required
Digital Television
- An error rate of 10-8^ or one bit in 100 million
bits is practically undetectable
- Channel error rates of 10 -5^ still permit
acceptable pictures, especially if error
correction techniques are used
- An analog TV signal requires a channel with a
signal-to-error ratio (SER) of 55dB
Digital Television
- If we use PCM for a digital television signal,
the principal source of error is due to
quantization
- The error is a maximum of + or - 1/2 the least significant bit
- For a quantization level of 8 bits, this is + or - 0.2%
- This “fine” quantization would appear as white noise if viewed as a picture