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Digital Image and Video Coding

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Digital Image and Video Coding 11. Basics of Video Coding H. Danyali hdanyali_at_ieee.org * During the transition from monochrome to color television, certain ... – PowerPoint PPT presentation

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Title: Digital Image and Video Coding


1
Digital Image and Video Coding
  • 11. Basics of Video Coding
  • H. Danyali
  • hdanyali_at_ieee.org

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  • This lecture is based on the material provided
    in

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Outline
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Global motion compensation
  • In global motion compensation, the motion model
    basically reflects camera motions such as
  • Dolly - moving the camera forward or backwards
  • Track - moving the camera left or right
  • Boom - moving the camera up or down
  • Pan - rotating the camera around its Y axis,
    moving the view left or right
  • Tilt - rotating the camera around its X axis,
    moving the view up or down
  • Roll - rotating the camera around the view axis
  • It works best for still scenes without moving
    objects.
  • There are several advantages of global motion
    compensation
  • It models the dominant motion usually found in
    video sequences with just a few parameters. The
    share in bit-rate of these parameters is
    negligible.
  • It does not partition the frames. This avoids
    artifacts at partition borders.
  • A straight line (in the time direction) of pixels
    with equal spatial positions in the frame
    corresponds to a continuously moving point in the
    real scene. Other MC schemes introduce
    discontinuities in the time direction.
  • Moving objects within a frame are not
    sufficiently represented by global motion
    compensation. Thus, local motion estimation is
    also needed.

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Nearest neighbor interpolation
Pixel enlargement
Original
overlap
zoomed
A grid Size the same as the original
image Pixels the same as the zoomed image
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Linear interpolation
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Bilinear interpolation
  • bilinear interpolation is an extension of linear
    interpolation for interpolating functions of two
    variables on a regular grid. The key idea is to
    perform linear interpolation first in one
    direction, and then again in the other direction.
  • generates an image of smoother appearance that
    nearest neighbour
  • requires 3 to 4 times the computation time of the
    nearest neighbour method

See interp2 function in Matlab
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The search for standardsthe FCC the NTSC
  • 1953 - The NTSC standard had to be revised to
    adapt to color TV.
  • Engineers split the signal into two components
    luma, which contained the brightness information,
    and chrominance, which contained the color
    information.
  • Field refresh rate of 60 Hz was slowed down by a
    factor of 1000/1001 to 59.94 Hz.
  • Broadcast television downshifted from 30 to 29.97
    frames per second

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Same old standard(The song remains the same)
  • Many improvements were made in cameras,
    production and broadcast gear, and in television
    receivers
  • Despite advances, the quality of analog broadcast
    was still limited to the NTSC standard of 60
    fields and 525 horizontal scan lines
  • Stuck with more or less same standards created in
    1941.

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Same old standard(The song remains the same)
  • By the 1980s, manufacturers had been developing
    and using both analog and digital HD systems
  • It became clear that the replacement for analog
    would use digital television technology.
  • Needed a new set of standards to ensure
    compatibility.

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ATSC
  • Formed in 1982
  • The Advanced Television Systems Committee is a
    not-for-profit organization whose purpose is to
    develop standards for the transition to DTV.
  • Its published broadcast standards are voluntary
    unless adopted and mandated by the FCC.
  • ATSC proposed DTV Standard (A/53) that specifies
    the protocol for high-definition broadcasting
    through a standard 6MHz channel

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DTV
  • In December 1996, the FCC adopted standards
    proposed by the ATSC, mandating that broadcasters
    begin broadcasting digitally.
  • WRAL of Raleigh, North Carolina was the first
    station to broadcast in digital.
  • FCC terminated analog broadcasting 2009

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DTV, SDTV, HDTV
  • NTSC standards defined one analog format
  • ATSC created a framework supporting multiple
    digital formats
  • There is considerable confusion among consumers
    regarding SDTV, DTV and HDTV.
  • Broadcaster do not have to broadcast in HD, just
    in DTV.

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HDTV SDTV Comparison
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DTV formats
HDTV/SDTV Horizontal lines Vertical lines Aspect Ratio Frame Rate
SDTV 640 480 43 60p, 60i, 30p, 24p
SDTV 704 480 43 and 169 60p, 60i, 30p, 24p
HDTV 1280 720 169 60p, 30p, 24p
HDTV 1920 1080 169 60i, 30p, 24p
Note Non-integer formats (eg. 29.97) omitted for
clarity.
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About non-integreer field rates in NTSC video
During the transition from monochrome to color
television, certain interference constraints
needed to be satisfied among the horizontal,
sound, and color frequencies. These constraints
were resolved by reducing the 60.00 Hz field rate
of monochrome television by a factor of exactly
1000/1001 to create the color NTSC field rate of
about 59.94 Hz. This led to the dropframe
timecode that is familiar to anyone that has been
involved in videotape editing. http//www.poynton
.com/notes/video/Timecode/index.html
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About non-integreer field rates in NTSC video
When a transmitter broadcasts an NTSC signal, it
amplitude-modulates a radio-frequency carrier
with the NTSC signal just described, while it
frequency-modulates a carrier 4.5 MHz higher with
the audio signal. If non-linear distortion
happens to the broadcast signal, the 3.579545 MHz
color carrier may beat with the sound carrier to
produce a dot pattern on the screen. To make the
resulting pattern less noticeable, designers
adjusted the original 60 Hz field rate down by a
factor of 1.001 (0.1), to approximately 59.94
fields per second. This adjustment ensures that
the sums and differences of the sound carrier and
the color subcarrier and their multiples (i.e.,
the intermodulation products of the two carriers)
are not exact multiples of the frame rate, which
is the necessary condition for the dots to remain
stationary on the screen, making them most
noticeable. http//en.wikipedia.org/wiki/NTSCCol
or_encoding
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