Scanning in Television

Basics of Video Camera, Lights & Sound

Unit 1
Topic 6
Presentation by- Mohit Kishore Vatsa
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 Suggested Further Readings & References

• Belavadi, V. (2013). Video Production. New Delhi: Oxford

University Press.
• Donald, R., & Spann, T. (2000). Fundamentals of Television
Production. Wiley.
• Millerson, G. (1999). The Technique of Television Production.
London: Focal Press.
• Zettl, H. (2005). Television Production Handbook, Cengage
Learning.
• Source of Images: Video Basics, Sixth Edition Herbert Zettl

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 Objectives of the Lecture

• To explain the students about scanning in television

• To understand about Progressive and Interlaced scanning

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 Lecture Outcomes

After going through this lesson, a student shall be able to

understand:
• Scanning in Television
• Difference between Progressive and Interlaced Scanning

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 Electrical Differences

• Themain difference starts with the electrical power system that

runs behind the color transmissions.
• In the United States, electrical power is generated at 60 hertz.
• The signal behind the NTSC broadcast format is set to send out
60 fields per second.
• Most televisions use a interlaced system, so the NTSC signal
sends out 30 lines of the image, followed by another 30
alternating lines.

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 Electrical Differences (Contd..)

• Basically, that results in 30 frames of a complete image

appearing every single second.
• In Europe and other countries, electrical power is generated at
50 hertz.
• Televisions that utilize PAL as the broadcast format only
produce 25 frames of a complete image appearing every single
second.

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 Electrical Differences (Contd..)

• This causes problems with the proper display of motion, as it

makes actors move a bit faster because of the difference in
frames per second that are showing movement.
• If you are trying to watch a PAL movie on a NTSC television, you
need to add 5 frames per second, or the motion of the film will
be very jerky or slow.

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 Resolution Quality Difference

• WhilePAL produces fewer frames per second than NTSC, it

produces more lines.
• AnNTSC television will broadcast 525 lines of resolution, while a
PAL television will broadcast 625 lines of resolution.

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 Resolution Quality Difference
(Contd..)

• As the lines of resolution increase, so does the amount of visual

information. This produces better picture quality and screen
resolution.
• If you were to try to convert an NTSC movie to PAL, black bars
would most likely be added to compensate for the smaller
screen aspect.
• The black bars would resemble what you would see in a
widescreen or letterbox movie.

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 Progressive Scanning System
• The electronic beams scans each line, much like the way you read.
• It
starts with the top left of the screen and scans the first line,
then jumps back to the left at the start of the second line and so
on.
• Afterthe last line has been scanned, the beam jumps back to its
original starting point at the top left of the screen.
• The beam scans all lines progressively.

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 Progressive Scanning System (Contd..)

• Contrary to interlaced scanning, which produces half a frame

(one field) for each scanning cycle, progressive scanning reads
all the lines and produces a full frame for each scanning cycle.
• The number of frames progressively scanned per second is
called the refresh rate.

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Progressive Scanning System (Contd..)

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 Retrace and Blanking

• The repositioning of the beam from the end of the scanned line
to the starting point of the next is called horizontal retrace.
• When the beam reaches the end of the last line and jumps back
to the starting point of the line one; it is referred to as vertical
retrace.

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 Retrace and Blanking (Contd..)

• Toavoid any picture interference during the horizontal and

vertical retraces, the beam is automatically starved so that it
won’t light up any pixels.
• This process is called blanking.
• Hence,horizontal blanking happens during horizontal retrace
and vertical blanking during the vertical retrace.

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 The Interlaced Scanning System
• Unlike a person reading line by line from top to bottom, in
interlaced scanning the electron beam skips every other line
during its first scan, reading only the odd-numbered lines.
• The beam returns to the top of the screen and reads all the
even-numbered lines.
• Scanning all the odd-numbered lines yields one field.
• The subsequent scanning of all the even-numbered lines
produces another field.
• The two fields compose one complete picture, called a frame

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The Interlaced Scanning System

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 The Scanning Process in Television
• In video, the illusion of streaming pictures (which in turn
creates and illusion of movement) is created by a scanning
process.
• The video scanning process creates a series of 25 frames in 1
second.
• The video frame does not exist as a single, discrete frame like a
motion picture frame.
• It is broken into 625 lines of information that are scanned one
line at a time, line by line, as the electronic beam moves across
and down the image on the target areas.

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 The Scanning Process

• To minimize brightness variations, each video frame is broken

into two fields, each composed of half the 625 lines in the
frame.
• The first field contains the 312.5 odd-numbered lines (1,3,5,
and so on), and the second field contains the 312.5 even-
numbered lines (2,4,6, and so on).

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 The Scanning Process (Contd..)

• When the electron beam reaches the end of the first line
(moving horizontally from left to right), it goes into a blanking
mode and then moves back across to the left edge to begin
scanning the next line down.
• During the horizontal blanking interval, the electron beam is
momentarily shut off so that it cannot be seen as it moves back
across the target to the next line.

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 The Scanning Process (Contd..)

• The process continues until the beam reaches the end of the last
line in the odd-numbered field.
• The beam than goes into vertical blanking interval while it
moves back to the top of the even-numbered field to begin he
downward again.

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 The Scanning Process (Contd..)

• The entire scanning process takes at unimaginable speed. Two

fields make one frame.
• In 1 second the electron beam scans 50 fields to create the 25
video frames.
• A process called interlaced scanning produces the full video
frame in 1/25 of a second.
• Thus, 25 frames are produced in one second. Which in turn
lends movement to the image.

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 Digital Video Scanning Systems

• Digital video, also called digital television (DTV), is generally

superior in quality to analog systems, not all digital video is
high-definition television (HDTV).
• Generally, DTV has become synonymous with superior picture
quality.
• One of the reasons for the improved quality of digital video
over standard television (STV) is that DTV has a higher picture
resolution (sharper picture detail), truer color, and a wider
contrast ratio (more subtle grays between the brightest and
darkest picture areas).
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 Digital Video Scanning Systems (Contd..)

• Three DTV systems have emerged as the most practical for all
kinds of video production: the 480p and the 720p systems
(p stands for progressive scanning) and the 1080i system
(i stands for interlaced scanning).
• 480p system: The picture of the 480p system is composed of
480 visible lines (just about what you actually see of the 525
lines of the standard analog system) that are progressively
scanned.
• It normally produces 60 complete frames (not fields) per
second.
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 Digital Video Scanning Systems (Contd..)

• 720p system: The 720p system produces 720 visible lines that
are progressively scanned.
• Its normal refresh rate is 60 frames per second.
• The high number of lines results in very sharp pictures that are
absolutely high-definition.
• The 720p system is in the HDTV category.

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 Digital Video Scanning Systems (Contd..)

• 1080i system: The 1080i system uses interlaced scanning to save

bandwidth.
• This means that its signals can be transported through a smaller
pipeline than if its scanning were progressive.
• Although the 1080i system produces only 30 frames (60 fields) or
less per second, its extremely high number of scanning lines
contributes to higher-definition video than with either the 480p or
the 720p system.

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 Digital Video Scanning Systems (Contd..)

• 720p system (Contd..): It is currently the highest-quality

broadcast HDTV system.
• Video quality also depends on the number of pixels that make
up each scanning line and on how little, or how much, the
video signal is compressed.
• The more compression imposed on a signal, the less high-
fidelity it become

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(Source: Herbert Zettl, Television Production Handbook, 9th Edition)
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 Interlaced Scanning

(Source: Herbert Zettl, Television Production Handbook, 9th Edition)

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Thank you

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