DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Yl
G
G
Figure 26.1 B’-Y’, R’-Y’
components for Rec. 709 HDTV
+1
R
-1 0
-1
R’-Y’ axis
+0.7874
B’-Y’, R’-Y’ components for Rec. 709 HDTV
The B’-Y’ component reaches its positive maximum at
blue (R’ =0, G’ =0, B’ = 1). With Rec. 709 luma coefficients,
the maximum of B’-Y’ = +0.9278 occurs at
Y’ = 0.0722. The B’-Y’ component reaches its negative
maximum at yellow (B’-Y’ =-0.9278). Analogously, the
extrema of R’-Y’ occur at red and cyan at values
±0.7874. (See Figure 26.1 above). These are inconvenient
values for both digital and analog systems. The
709 Y’PBP R and 709 Y’C BC R systems to be described both
employ versions of [Y’, B’-Y’, R’-Y’] that are scaled to
place the extrema of the component values at more
convenient values.
To obtain [Y’, B’-Y’, R’-Y’], from R’G’B’, for Rec. 709
luma coefficients, use this matrix equation:
⎡ 709
Y'
⎤
⎢ ⎥
⎡ 0. 2126
⎢ 709
B'−Y'⎥ ⎢
= 0 2126
⎢ ⎥
⎢−
.
709
⎢R'−Y'⎥
⎢
⎣
0. 7874
⎣ ⎦
0. 7152
−0.
7152
−0. 7152
0. 0722⎤
⎡R'⎤
⎥ ⎢ ⎥
0. 9278⎥
• ⎢G'⎥
−0.
0722⎥
⎢
⎦ ⎣
B'⎥
⎦
PBPR components for Rec. 709 HDTV
If two color difference components are to be formed
having excursions identical to luma, then P B and P R
314 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES
Cy
Mg
+0.9278
B +1
B’-Y’ axis
Eq 26.1