DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

FILM FRAMES
VIDEO FIELDS
Figure 36.2 Vertical/temporal
relationships of 2-3 pulldown.
Time is on the x-axis;
vertical displacement is on the
y-axis. 2-3 pulldown, shown
on the left, introduces
temporal discontinuities. The
“dual-port” approach, on the
right, introduces spatial
discontinuities.
2-3 PULLDOWN “DUAL-PORT”
A B
A
B
0 1 2 3 4 0 1 2 3
FILM
VIDEO
camera, this technique won’t work. The right portion of
Figure 36.2 indicates lines scanned from film being
written into a framebuffer. The slanted dashed lines
intersect the video scanning; at the vertical coordinate
where the lines intersect, the resulting picture switches
abruptly from one field frame to another. This results in
output fields that contain spatial discontinuities.
(Although this description refers to interlaced scanning,
none of these effects are directly related to interlace:
Exactly the same effects are found in progressive
systems.)
Figure 36.2 shows the vertical-temporal (V·T) relationships
of 2-3 pulldown, with time on the horizontal axis,
and vertical dimension of scanning on the vertical axis.
Dashed lines represent film sampling; solid lines represent
video sampling. Film capture samples the entire
picture at the same instant. The staggered sequence
introduced by 2-3 pulldown is responsible for the irregular
spacing of the film sample lines. In video, sampling
is delayed as the scan proceeds down the field; this is
reflected in the slant of the lines of Figure 36.2.
In deinterlacing for a dedicated display, the output
frame rate can be locked to the input video frame rate
of 59.94 Hz or 50 Hz. But in desktop computing applications
of deinterlacing, the output rate cannot be
forced to match the native video rate: the output is
generally higher than 60 Hz, and asynchronous to the
432 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES
VIDEO
FILM
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