DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

ITU-R Rec. BT.601-5, Studio
encoding parameters of digital television
for standard 4:3 and widescreen
16:9 aspect ratios.
fH,480i : fH,576i 525 :
:
:
144 : 143
Table 31.1 Derivation of 13.5 MHz common sampling rate
60 1000
× ×
2 1001
625 50
×
2
2 3 3
2 5⋅3⋅2 5 ⋅ 2
7× 5 × 3× ×
2 13⋅11⋅7 2
4 5 × 2
5 ×
2
3 3 2 4
× × 13 ×
11
a rate high enough to ease the design of analog antialiasing
filters and low enough to minimize data rate
and memory requirements.
At 13.5 MHz, 480i video has 858 samples per total
line, and 576i video has 864 S TL. Fortunately, the
blanking tolerances between NTSC and PAL accommodate
a choice of 720 samples per active line (S AL) in
both systems. Standardization of this number of active
samples results in a high degree of commonality in the
design of video processing equipment, since only the
difference in active line counts needs to be accommodated
to serve both 525 and 625 markets. Also the
technically difficult problem of standards conversion is
eased somewhat with a common sampling frequency,
since horizontal interpolation becomes unnecessary.
However, blanking must be treated differently in the
two systems to meet studio interchange standards.
Numerology of HDTV scanning
Figure 31.1 overleaf gives a graphic representation of
the development of the magic numbers in HDTV. At the
upper left is the AC power line frequency in North
America, and the small integer factors of 525. Next to
that is indicated the AC power frequency in Europe,
and the small integer factors of 625. HDTV was originally
conceived as having twice the horizontal and
twice the vertical resolution of conventional television:
At the top right is the conceptual origin of the total
number of HDTV scanning lines as twice the geometric
mean of 525 and 625. North America would have
preferred twice 525 and Europe twice 625; the
CHAPTER 31 FRAME, FIELD, LINE, AND SAMPLE RATES 377