DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Computing
notation
640 480
480i 29.97
Video
notation
525/59.94
Figure 6.9 My scanning
notation gives the count
of active (picture) lines, p for
progressive or i for interlace,
then the frame rate. Because
some people write 480p60
when they mean 480p59.94,
the notation 60.00 should
be used to emphasize a rate
of exactly 60 Hz.
Since all 480i systems have a frame
rate of 29.97 Hz, I use 480i as
shorthand for 480i29.97. Similarly,
I use 576i as shorthand for 576i25.
Figure 6.10 Test scene
hertz. (Interlace is implicit unless a slash and 1:1 is
appended to indicate progressive scanning; a slash and
2:1 makes interlace explicit.) 525/59.94/2:1 scanning is
used in North America and Japan; 625/50/2:1 prevails
in Europe, Asia, and Australia. Until very recently, these
were the only scanning systems used for broadcasting.
Recently, digital technology has enabled several new
scanning standards. Conventional scanning notation
cannot adequately describe the new scanning systems,
and a new notation is emerging, depicted in Figure 6.9:
Scanning is denoted by the count of active (picture)
lines, followed by p for progressive or i for interlace,
followed by the frame rate. I write the letter i in lowercase,
and in italics, to avoid potential confusion with
the digit 1. For consistency, I also write the letter p in
lowercase italics. Traditional video notation (such as
625/50) is inconsistent, juxtaposing lines per frame with
fields per second. Some people seem intent upon
carrying this confusion into the future, by denoting the
old 525/59.94 as 480i59.94. In my notation, I use
frame rate.
In my notation, conventional 525/59.94/2:1 video is
denoted 480i29.97; conventional 625/50/2:1 video is
denoted 576i25. HDTV systems include 720p60 and
1080i30. Film-friendly versions of HDTV are denoted
720p24 and 1080p24. Aspect ratio is not explicit in the
new notation: 720p, 1080i, and 1080p are implicitly
16:9 since there are no 4:3 standards for these systems,
but 480i30.00 or 480p60.00 could potentially have
either conventional 4:3 or widescreen 16:9 aspect ratio.
Interlace artifacts
An interlaced camera captures 60 (or 50) unique fields
per second. If a scene contains an object in motion with
respect to the camera, each field carries half the
object’s spatial information, but information in the
second field will be displaced according to the object’s
motion.
Consider the test scene sketched in Figure 6.10,
comprising a black background partially occluded by
a white disk that is in motion with respect to the
60 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES