DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Coding extends to 1.3 times the
picture excursion; it does not
extend to 4 ⁄3. Apparently the choice
of axes for modulated chroma
prevents excursion beyond 1.3;
however, I cannot find any authoritative
technical reference to this.
parts of PAL; if the two signals are summed, a legal PAL
signal results:
( )
7 601 3
Y'S-video-625 = Y' + −sync
10 10
Eq 44.2
7 3 ⎛ burst⎞
CS-video-625 = C +
10 10
⎜
⎝ 2
⎟
⎠
Composite PAL encoding
A composite PAL signal is formed by summing luma (Y’)
and modulated chroma (C) signals, along with sync and
colorburst.
The picture-to-sync ratio for PAL is 7:3, leading to
a composite signal formed as follows, where sync is
taken to be unity when asserted and zero otherwise,
and burst is in the range ±1:
7
PAL = ⎛ 601
Y' + C⎞
10 ⎝ ⎠
3 ⎛ burst ⎞
+ ⎜ − sync
10
⎟
⎝ 2 ⎠
Composite digital PAL interface (4fSC) Digital composite PAL – also known as the 576i version
of 4fSC – is formed by scaling and offsetting
Equation 44.3 so that blanking in an 8-bit system (zero
in the equation) is at codeword 64 and reference white
is at codeword 211. Luma excursion is 147 codes. In
a 10-bit system, these levels are multiplied by four: The
reference levels have two low-order zero bits
appended. Codewords having the 8 most-significant
bits all-one or all-zero are prohibited from video data.
Figure 44.1 opposite shows a waveform drawing of
luma in a 576i composite digital interface.
Each line has 948 S AL , of which the central 922 or so
encompass the picture width.
Composite digital 4f SC PAL systems sample on the
[U+V, U-V] axes – that is, sampling is coincident with
the 45°, 135°, 225°, and 315° phases of subcarrier. Burst
samples lie at the 0°, 90°, 180°, and 270° phases of
burst, and take 8-bit values {95.5, 64, 32.5, 64}.
532 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES
Eq 44.3