Digital Video
•Digital video is basically 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 Computing - Lecture Slides, Slides of Multimedia Applications
Multimedia Computing, In this short course we study the basic concept of the principle of computer architecture. In these lecture slides the key points cover in these slides are:Digital Video, Principles of Analog, Digital Image Processing, Television Fundamentals, Interlaced Scanning, Television Transmission, Complete Frame, Deinterlacing, Scan Lines Per Frame, Signal-To-Error Ratio
Typology: Slides
2012/2013
1 / 71
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Digital Video
- Digital video is basically 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, use interlaced scanning as opposed 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
Deinterlacing
- There are several common
operations that you might want to
perform on interlaced video
- Producing stills
- resizing the video
- changing the frame 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
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 would digital transmission compare to today’s 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
Digital Television
- A bit error rate of 10-8^ is practically undetectable
- From the figure above, this requires a SER of only 21 dB
- If we use the rate 10-5^ with error correction bits added, a SER of 18 dB may be sufficient
- This requires less than 1 bit/pixel
- The essential problem in digital TV coding is therefore to reduce the picture bandwidth at the expense of the bit error rate and retain acceptable picture quality
Aspect Ratios
- Each of the systems listed above has an aspect
ratio (ratio of width to height) of 4:
- Cinematic films and high-definition television