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Sec. 8–9 Television 639
from the quadrature modulation technique that is used to modulate them onto a subcarrier.)
The exact equations used for these signals can be expressed in matrix form:
m y (t) 0.3 0.59 0.11 m R (t)
m i (t)
J
m q (t) K = 0.6 -0.28 -0.32
J
0.21 -0.52 0.31 K m G (t)
J
m B (t) K
(8–63)
⎧
⎪⎪⎪⎨⎪⎪⎪⎩
M
where M is a 3 × 3 matrix that translates the red, green, and blue signals to the brightness,
in-phase, and quadrature phase video (baseband) signals. For example, from Eq. (8–63), the
equation for the luminance (black-and-white) signal is
m y (t) = 0.3m R (t) + 0.59m G (t) + 0.11m B (t)
(8–64)
Similarly, the equations for m i (t) and m q (t), which are called the chrominance signals, are easy
to obtain. In addition, note that if m R (t) = m G (t) = m B (t) = 1, which corresponds to maximum
red, green, and blue, then m y (t) = 1, which corresponds to the white level in the black-andwhite
picture.
The chrominance components are two other linearly independent components, and if
they are transmitted to the color TV receiver together with the luminance signal, these three signals
can be used to recover the red, green, and blue signals using an inverse matrix operation.
The bandwidth of the luminance signal needs to be maintained at 4.2 MHz to preserve sharp
(high-frequency) transition in the intensity of the light that occurs along edges of objects in the
scene. However, the bandwidth of the chrominance signals does not need to be this large, since
the eye is not as sensitive to color transitions in a scene as it is to black-and-white transitions.
According to NTSC standards, the bandwidth of the m i (t) signal is 1.5 MHz, and the bandwidth
of m q (t) is 0.5 MHz. When they are quadrature-modulated onto a subcarrier, the resulting
composite baseband signal will then have a bandwidth of 4.2 MHz. (The upper sideband of the
in-phase subcarrier signal is attenuated to keep a 4.2-MHz bandwidth.)
The composite NTSC baseband video signal is
where
m c (t) = e m s(t),
m y (t), + Re{g sc (t)e jv sc t }
during the sync interval
during the video interval f
(8–65)
g sc (t) = [m i (t) - jm q (t)]e j33°
(8–66)
Equation (8–66) indicates that the chrominance information is quadrature modulated onto a subcarrier
(as described in Table 4–1). m s (t) is the sync signal, m y (t) is the luminance signal, and
g sc (t) is the complex envelope of the subcarrier signal. The subcarrier frequency is f sc = 3.579545
MHz ± 10 Hz, which, as we will see later, is chosen so that the subcarrier signal will not interfere
with the luminance signal even though both signals fall within the 4.2-MHz passband.
In analog broadcast TV, this composite NTSC baseband color signal is amplitude modulated
onto the visual carrier, as described by Eq. (8–61) and shown in Fig. 8–31. In
microwave relay applications and satellite relay applications, this NTSC baseband signal is