DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Concerning the association of
U with sin and V with cos, see the
marginal note on page 339.
Color differences (U, V)
Color differences for S-video-525 and NTSC are
computed by scaling B’-Y’ and R’-Y’ components to
form U and V, as I described in UV components, on
page 336. This scaling limits the maximum value of the
composite signal, to be defined in Composite NTSC
encoding, on page 515, to the range - 1 ⁄3 to + 4 ⁄3. The
scale factors would cause 100% colorbars to have an
excursion from -33 1 ⁄3 IRE to +133 1 ⁄3 IRE, were it not
for the scaling by 37 ⁄40 (i.e., 0.925) that occurs when
setup is introduced. (Setup will be detailed on
page 514.)
The + 4 ⁄3 limit applies to composite studio equipment; a
limit of +1.2 applies to terrestrial (VHF/UHF) broadcast.
Color difference filtering
The U and V color difference components are subject to
lowpass filtering with the following attenuation:
• Less than 2 dB at frequencies less than 1.3 MHz
• At least 20 dB at frequencies greater than 3.6 MHz
In the studio, where 4.9 MHz or more of composite
bandwidth is maintained, 1.3 MHz of chroma bandwidth
is available. However, terrestrial VHF/UHF transmission
of NTSC limits composite bandwidth to
4.2 MHz. Even if 1.3 MHz of chroma is encoded, upon
filtering to 4.2 MHz, [U, V] chroma crosstalk is introduced:
Only 600 kHz of crosstalk-free chroma is transmitted.
These issues were detailed in NTSC Y’IQ system,
on page 365.
Chroma (C )
As I explained in NTSC chroma modulation, on
page 338, in NTSC, U and V color difference components
are combined into a single chroma signal:
C = Usin ωt+ Vcos ωt; ω = 2π
fSC
Eq 42.1
sin ωt and cos ωt represent the 3.58 MHz color
subcarrier defined in Subcarrier, on page 511.
CHAPTER 42 480 i NTSC COMPOSITE VIDEO 513