The Television System

1
The Television System

• the television system
• analog and digital signals
• the camera
• lenses

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Monochrome Image
Approximately 500 dots per line
525 Horizontal lines
250,000 illumination points
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Image formation by the TV receiver
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Monochrome Image
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Image formation for color TV
Shadow Mask
Blue dot
Red gun
Green dot
Green gun
Blue gun
Red dot
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Interlaced Scanning

• The electron beam first scans all odd-numbered
  lines, from left to right and top to bottom. This
  scanning cycle produces the first field (1/60th
  of a second).
• The beam jumps back to the top and scans all
  even-numbered lines. The second cycle produces
  the second field (1/60th of a second).
• The two fields make up a complete television
  picture, called a frame (1/30th of a second).

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Interlaced Scanning
1st field 1/60th of a second
2nd field 1/60th of a second
1 TV frame 1/30th of a second 30 frames/second
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Interlaced Progressive Scanning

• In interlaced scanning, the beam reads every
  other line from top to bottom. Each scan produces
  one field. Two fields make up a complete frame.
• In progressive scanning the beams reads every
  line from top to bottom. Each complete scan
  produces a television frame. Retrace lines are
  blanked out so they do not appear on the screen.

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Picture Quality
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Vertical Detail
Vertical stack vertical detail
Lines of Resolution To measure vertical detail,
we count the vertical stack of horizontal lines.
The more lines the vertical stack contains, the
higher the resolution. The NTSC system has 525
lines, of which only 480 are visible
on-screen. HDTV has 1,080 active (visible) lines.
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Horizontal Detail
Lines of Resolution To measure horizontal detail,
we count the dots (pixels) of each horizontal
line and then connect them vertically, which
yields a horizontal stack of vertical lines. The
more lines the horizontal stack contains, reading
from left to right, the higher the
resolution. This horizontal stack can contain
many more lines (such as700) than can the
vertical stack.
Horizontal stack horizontal detail
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White and Black Levels

• The waveform monitor shows a graph of the
  luminance (black-and-white) portion of the video
  signal.
• It also shows the white level (the upper limit of
  the signal) and the black level (the lower limit
  of the signal).

White level100
Black level7.5 Zero level
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Analog and Digital Signals

• The analog signal can be represented by a ramp
  that leads continuously to a certain height.
• The digital signal can be represented by a
  staircase that lead to certain height in discrete
  steps.

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Analog and Digital Signals
Electronic signals as they originate in
microphones and cameras are analog in form. This
means that the equipment detects signals in terms
of continuing variations in relative strength or
amplitude. In audio this would be loudness in
video it would be (among other things) the
brightness component of the picture.
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Analog and Digital Signals
The top part of the illustration on the left
shows how an analog signal can smoothly rise and
fall over time to reflect changes in the original
audio or video source. Compared to the digital
signal at the bottom, an analog signal would seem
to be the most accurate and ideal representation
of the original signal.
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Analog - Noise
The problem arises in the need for constant
amplification and re-amplification of the signal
throughout every stage of the audio and video
process.
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Convert to Digital
By converting the original analog signals into
digital form, this noise buildup can be virtually
eliminated, even though it is amplified and
"copied" thousands of times. Since digital
signals are limited to the form of zeros and ones
(0's and 1's), no "in between" information can
creep in to degrade the signal.
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SDTV HDTV
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Digitizing Diagram

• The digitization of an analog signal is a
  four-step process
• anti-aliasing
• sampling
• quantizing
• coding.

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1. Anti-aliasing

• In anti-aliasing the extreme frequencies of the
  analog signal that are unnecessary for its proper
  sampling are filtered out.

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2. Sampling
Red line represents relatively low data loss
Red line represents greater data loss

• Sampling selects portions of the the original
  analog signal. A low sampling rate transforms the
  ramp into a few large steps. Much of the original
  signal is lost
• A high sampling rate selects more parts of the
  original signal. The ramp is made of more,
  smaller steps, making the steps look more like
  the original ramp. The higher the sampling rate,
  the higher the signal quality.

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3. Quantizing

• Quantizing assigns the selected signal samples a
  fixed position. This is the step building phase.
  Each step gets a particular decimal number,
  indicating its height.
• Low sampling rate several large steps.
• High sampling rate many small steps.

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4. Coding or Encoding

• Coding assigns each step a binary number 0 or 1.

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DTV Scanning Formats

• 480p
• 480 lines progressively scanned.
• 720p
• 720 lines progressively scanned
• 1080i
• 1,080 lines with interlaced scanning.
• All have 169 aspect ratio but can be switched to
  the traditional 43 ratio.

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Additive Color Mixing
Red
Yellow
Magenta
White
Green
Blue
Cyan
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Color Attributes
Hue
Brightness
(Light reflectancehow light or dark a color
appears on the grayscale)
Luminance
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Parts of the camera
Viewfinder
Imaging device
Lens
Camera
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Basic camera functions
Viewfinder
Object
Lens
Processor
Amplifier
Beam splitter
Charge-coupled devices (CCDs)
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Camera Chain
Sync Generator
CCU
Camera head
Power supply
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Beam Splitters
CCD for red channel
Beam-splitting prism block
CCD for green channel
Zoom lens
CCD for blue channel
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Striped and Mosaic Filters
Mosaic RGB Filter
Striped RGB Filter
Most consumer cameras have only one imaging chip
(CCD) and use a striped or mosaic-like filter
instead of the prism block to divide the white
light into RGB color beams. Each of these colored
beams is then transduced (changed) by the single
CCD into the RGB signals.
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CCD Process
The charge-coupled device consists of an imaging
area (the window), a storage area, and an output
area. The imaging area contains the pixels, the
storage area stores the pixel charges, and the
output area delivers them to the amplifier to
form the video signal.
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Brightness Insufficient Contrast
Although the hue is sufficiently different for
this letter to show up on the blue background of
the color television set, it is barely readable
on a black-and-white receiver. The brightness
contrast is insufficient for good monochrome
reproduction.
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Brightness Good Contrast
The hues in this picture have enough difference
in brightness to show up equally well on both a
color and black-and-white receiver.
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Focal Length
Optical center of lens
Distant image in focus
Focal length
Lens with focus set at infinity
CCD imaging device
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Wide-Angle Narrow-Angle Zoom Positions
Wide angle
Narrow angle
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The Law of Lenses
The shorter the lens...
The longer the lens...
the narrower the angle...
the wider the angle...
the more in the picture...
the less in the picture...
the smaller the subject
the larger the subject
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Focal LengthWide Angle
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Focal LengthNarrow Angle
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Focal LengthNormal Angle
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Elements of a Variable Focal Length Lens
Focusing lens
Beam-splitting prism
Relay lens
Variator lens
Variator lens
Focusing lens
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Variable Focal Length Lens
Zoom
Focus
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Exposure Control
Aperture
Iris
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Exposure Control
Aperture
Iris
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f-Stop2.8
The smaller the f-stop number the larger the iris
opening
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f-Stop16
The larger the f-stop number the smaller the iris
opening
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Depth-of-Field
Point of Focus
The Depth-of-Field is the area within which all
objects, although located at different distances
from the camera, are in focus.
Depth-of-Field (area in focus)
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Depth-of-Field
z-axis
in focus
z-axis
in focus
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Large Depth-of-Field
IN FOCUS
camera
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Narrow Depth-of-Field
IN FOCUS
camera
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Depth-of-Field
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Depth-of-Field is influenced by

• aperture setting
• subject to camera distance
• focal length of the lens

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Depth-of-Field is influenced by the aperture
setting

• the larger the aperture opening, the shallower
  the depth-of-field.

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Depth-of-Field is influenced by the subject to
camera distance

• the closer the camera to the subject, the
  shallower the depth-of-field.

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Depth-of-Field is influenced by the focal length
of the lens

• the longer the lens, the shallower the
  depth-of-field.

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Depth-of-Field is influenced by

• subject to camera distance
• the closer the camera to the subject, the smaller
  the depth-of-field
• focal length of the lens
• the longer the lens, the shallower the
  depth-of-field
• aperture
• the larger the aperture opening, the shallower
  the depth-of-field

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Wide-angle Distortion
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The narrow-angle lens compresses space
normal-angle
narrow-angle
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Wide-angle vs. Narrow-angle
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Narrow-angle vs. Wide-angle
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Narrow-angle vs. Wide-angle
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Movement

• Wide-angle
• Good dolly lens it de-emphasizes camera jitter
  and wobble.
• Objects moving toward or away from the camera
  have their speed greatly accelerated.
• Narrow-angle
• Objects moving toward or away from the camera
  seem to move much more slowly.