DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

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EBU Tech. 3280, Specification of
interfaces for 625-line digital PAL
signals.
1
922 S PW
83 + 0H 948 SAL Sample clocks, 17.734475 MHz
1135.0064 STL Figure 44.1 576i, 4f SC PAL digital waveform, showing the range of the luma component.
The chroma component will contribute to excursions outside this range.
Owing to the complex relationship in “mathematical
PAL” between subcarrier frequency and line rate,
sampling in 4f SC PAL is not line-locked: There is a noninteger
number (1135 4 ⁄625) of sample periods per total
line. (If analog sync were digitized, it would take
different sets of values on different lines.) At a digital
interface, we would prefer to have the same integer of
sample periods per line in every line. 4f SC PAL standards
approximate this situation: TRS sequences define
lines at the interface having the same number of sample
periods per line (1135) in all but two lines in each field.
Two lines per frame contain 1137 samples each – one
line among {625, 1, 2, 3, 4}, ideally line 625, and one
line among {313, 314, 315, 316, 317}, ideally line 313.
The two extra samples take blanking value; they are
inserted immediately prior to the first active sample of
the associated line. SMPTE 259M allows some flexibility
on the location of the extra pairs; however, EBU
Tech. 3280 mandates that the extra pairs are on lines
625 and 313. Be liberal on what you accept and
conservative on what you produce.
With conventional sample numbering, where sample 0
is the leftmost active sample in a line, 0 H falls between
samples 957 and 958. The first word of TRS-ID is at
sample 967.
CHAPTER 44 576 i PAL COMPOSITE VIDEO 533