NTSC (1)

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NTSC (1)

• NTSC 21 interlaced, 525 lines per frame, 60
  fields per second, and 43 aspect ratio
• horizontal sweep frequency, fl, is 525 ? 30
  15.75 kHz, 63.5 ?s to sweep each horizontal line.
• horizontal retrace takes 10 ?s, that leaves 53.5
  ?s ( ) for the active video signal per line.
• Only 485 lines out of the 525 are active lines,
  40 (20?2) lines per frame are blanked for
  vertical retrace.
• The resolvable horizontal lines, 485 ? 0.7
  339.5 lines/frame, where 0.7 is the Kell factor.
• The resolvable horizontal lines, 339 ? 4/3
  (aspect ratio) 452 elements/line.

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NTSC (2)

• NTSC 21 interlaced, 525 lines per frame, 60
  fields per second, and 43 aspect ratio. The
  bandwidth of the luminance signal is
  452/(2?53.5?10-6) 4.2 MHz.
• The chrominance signals, I and Q can be low-pass
  filtered to 1.6 and 0.6 MHz, respectively, due to
  the inability of the human eye to perceive
  changes in chrominance over small areas (high
  frequencies).
• Modulation vestigial sideband modulated (VSB),
  quadrature amplitude modulated (QAM).

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NTSC Video Signal
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Digital Video

• There is no need for blanking or sync pulses.
• It has the aliasing artifacts due to lack of
  sufficient spatial resolution.
• The major bottleneck of the use of digital video
  is the huge storage and transmission bandwidth
  requirements.
• digital video coding concerning the efficient
  transmission of images over digital communication
  channels.

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Digital Video, CCIR601

• Sampling rate fs fs,xfs,yfs,t fs,xfl.
• Two constraints (1) ?x ?y (2)for both NTSC
  and PAL.
• (1) ? fs,x ? IAR fs,y, or fs IAR (fs,y)2fs,t,
  which leads to fs ? 11 (NTSC) and 13 (PAL) MHz.
• So, fs 858fl (NTSC) 864 fl (PAL) 13.5 MHz.

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Fourier Analysis
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Fourier Transform Pairs
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Fourier Transform Pairs Limited Bandwidth
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Fourier Approximations
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Sampling Truncating Effect in FT (1)
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Sampling Truncating Effect in FT (2)
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Simple Condition for DFT FT

• The signal h(t) must be periodic, and
  band-limited,
• satisfying the Nyquist rate, and
• the truncation function x(t) must be nonzero over
  exactly one period of h(t).

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DFT VS. FT (1)

• Difference arises because of the discrete
  transform requirement for sampling and
  truncation.
• Case 1 Band-limited periodic waveform
  Truncation interval equal to period
• e.g. -T/2, T0-T/2.
• They are exactly the same within a scaling
  constant.

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DFT VS. FT (2)

• Case 2 Band-limited periodic waveform
  Truncation interval NOT equal to period
• The zeros of the sinf/f function are not
  coincident with each sample value.
• Leakage The effect of truncation at other than a
  multiple of the period is to create a periodic
  function with sharp discontinuities. The
  introduction of these sharp changes in the time
  domain results additional frequency components (a
  series of peaks, which are termed sidelobes.)

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DFT VS. FT (3)

• Case 3 Finite Duration Waveforms
• N is chosen equal to the number of samples of the
  finite-length function, T T0/N.
• Errors introduced by aliasing are reduced by
  choosing the sample interval T sufficiently
  small.

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DFT VS. FT (4)

• Case 4 General Waveforms
• The time domain function is a periodic where the
  period is defined by the N points of the original
  function after sampling and truncation.
• The frequency domain function is also a periodic
  where the period is defined by the N points whose
  values differ from the original frequency
  function by the error introduced in aliasing and
  truncation.
• The aliasing error can be reduced to an
  acceptable level by decreasing the sample
  interval T.

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periodic
periodic
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Leakage Reduction (1)

• Its inherent in the DIGITAL Fourier transforms
  because of the required time domain truncation.
• If the truncation interval is chosen equal to a
  multiple of the period, the frequency domain
  sampling function is coincided with the zeros of
  the sin(f)/f function do not alter the DFT
  results.
• If the truncation interval is NOT chosen equal to
  a multiple of the period, the side-lobe
  characteristics of the sin(f)/f frequency
  function result additional frequency components
  (leakage) in DFT domain.

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Leakage Reduction (2)

• To reduce this leakage it is necessary to employ
  a time domain truncation function which has
  side-lobe characteristics that are of smaller
  magnitude.
• The Hanning function The effect is to reduce the
  discontinuity, which results from the rectangular
  truncation function.

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DCT VS. DFT

• The spurious spectral phenomenon Sampling in
  frequency domain results an implicit periodicity.
  The effect of truncation at other than a multiple
  of the period is to create a periodic function
  with sharp discontinuities.
• To eliminate the boundary discontinuities, the
  original N-point sequence can be extended into a
  2N-point sequence by reflecting it about the
  vertical axis. The extended sequence is then
  repeated to form the periodic sequence, this
  sequence may not have any discontinuities at the
  boundaries.
• The symmetry implicit in the DCT results in two
  major advantages over the DFT (1) less spurious
  spectral components, and (2) only real
  computations are required.