DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Figure 30.1 IQ components
are formed by rotating, by
33°, the [U, V] components
depicted in Figure 28.1, on
page 336. According to the
conventions of communications
theory, I (for in-phase)
should be aligned with the
x-axis, and Q (for quadrature)
should be aligned with
the y-axis; however, in video
the rotation is followed by
an exchange of axes. This
sketch includes -I and +Q
vectors, at burst amplitude,
that are elements of SMPTE
colorbars; see page 537.
Eq 30.1
Some authors mistakenly omit the
exchange of B’-Y’ and R’-Y’ axes
in describing Y’IQ coding. Some
authors wrongly state or suggest
that Y’IQ is in use with linear-light
coding.
Eq 30.2
Eq 30.3
-0.5
G
Yl
Cy
+0.5
BURST BURST
IQ components
I axis (originally 1.3 MHz)
Figure 30.1 shows a plot of the IQ color difference
plane. The rotation and exchange from [U, V] to [I, Q]
is accomplished by this matrix transform of Y’UV
components:
⎡601
601
Y’ ⎤ ⎡1
0 0 ⎤ ⎡ Y’
⎤
⎢ ⎥ ⎢
⎥ ⎢ ⎥
⎢ I ⎥ = ⎢0
−0.
544639 0. 838671⎥
• ⎢ U ⎥
⎢ ⎥
⎢ ⎥
Q ⎢0
0 838671 0 544639 V
⎣⎢
⎦⎥
⎣
. . ⎥
⎦ ⎣⎢
⎦⎥
Owing to the exchange of axes, the matrix is its own
inverse: The same matrix recovers Y’UV from Y’IQ.
To encode Y’IQ from R’G’B’, the rotation and exchange
above are concatenated with the matrix of
Equation 28.4, on page 337:
To recover R’G’B’ from Y’IQ, invert Equation 30.2:
CHAPTER 30 NTSC Y’IQ SYSTEM 367
R
+Q phase
-I phase
-0.5
B
Mg
+0.5 Q axis (600 kHz)
⎡601
Y’ ⎤ ⎡0.
299 0. 587 0. 114 ⎤ ⎡R’
⎤
⎢ ⎥ ⎢
⎥ ⎢ ⎥
⎢ I ⎥ = ⎢0.
595901 −0. 274557 −0.
321344⎥
• ⎢G’
⎥
⎢ ⎥
Q ⎢0
0 0
B’
⎣⎢
⎦⎥
⎣
. 211537 − . 522736 . 311200⎥
⎢ ⎥
⎦ ⎣ ⎦
⎡R'⎤
⎡
⎤ ⎡601
1 0. 955986 0.
620825 Y'
⎤
⎢ ⎥ ⎢
⎥ ⎢ ⎥
⎢G'⎥
= ⎢1
−0. 272013 −0.
647204⎥
• ⎢ I ⎥
⎢
⎣
B'⎥
⎢
⎦ ⎣
−
⎥ ⎢ ⎥
1 1. 106740 1.
704230
⎦
Q
⎣⎢
⎦⎥