Datasheet

■ Resolutions and Frame Rates 11
support 24p, which records progressive frames at 24 fps. Other cameras offer 24p Advanced,
which records 24 fps by repeating frames with a 30 fps format.
The frame rate of PAL, SECAM, and DVB video and broadcast television is 25. The
ATSC HDTV formats 1080p, 1080i, and 720p, as well as 480p EDTV, support a frame
rate of 30. If the video is interlaced, 30 fps is sometimes expressed as 60, or 60 fields-per-
second.
Tips & Tricks: NTSC and ATSC Frame Rates
When a frame rate is listed for an NTSC or ATSC SDTV, EDTV, or HDTV format, it is usually
rounded off. Thus 30 fps is actually 29.97 fps and 24 fps is actually 23.98 fps. When whole-value
frame rates are listed for PAL or DVB formats, the frame rate is accurate. Note that 29.97 is a
simplification of the more accurate 30/1.001 and 23.98 is a simplification of 24/1.001.
Tips & Tricks: Frame Rate Conversions
Converting between frame rates has been a problem since the advent of television. Converting
from 24 fps to 30 fps requires a 3:2 pulldown, whereby frames must be duplicated. This leads to
hesitation in the motion known as judder. Converting from 30 fps to 24 fps requires the removal
or averaging of 6 frames per second. Converting between different international video and broad-
cast standards is equally difficult and often leads to some type of motion artifact. Thankfully,
recent improvements in time warping and optical flow techniques allow compositors to change
frame rates without unduly affecting the footage. For more information on time warping and
optical flow, see Chapter 12, “Advanced Techniques.”
Interlaced vs. Progressive
The process of interlacing breaks each
frame of video into two fields. One field
carries the even line numbers and a sec-
ond field carries the odd lines numbers
(see Figure 1.7). When interlaced footage
is broadcast or played as video, the fields
are displayed one at a time. Hence, NTSC
SDTV displays 60/1.001 fields per second
(often rounded to 59.94) and PAL SDTV
displays 50 fields per second. Interlacing
provides improved picture quality without
requiring additional bandwidth. In con-
trast, progressive frames are not split apart
but are displayed intact. CG renders, for
example, are generally delivered to a com-
positor as progressive frames.
Figure 1.7 Close-up of interlaced frame. The
footage features a rapid camera zoom in. If the
camera movement was slower, the interlacing
would be less perceptible.
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