DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Eq 23.7
Video signal, V’
1.2
1.0
0.8
0.6
0.4
0.2
0.081
0
-0.02025
-0.2
Figure 23.4 Rec. 1361
transfer function
160
219
5
2 · 5
=
73· 3
-0.0045
+0.018
Power function segment,
exponent 0.45
Linear segment,
slope 4.5
-0.2 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Tristimulus value, L (relative)
Encoding for Rec. 1361 is expressed in Equation 23.7:
⎧
045 .
⎪ 1. 099( −4
L)
− 0. 099
⎪−
; −025 . ≤ L < −0004
.
⎪
4
V'
1361 = ⎨4.
5L; −0. 0045 ≤ L<
0. 018
⎪
⎪ 045 .
1. 099L −0. 099 0 018 ≤ L<
1 33
⎪
; . .
⎩
The function is graphed in Figure 23.4 above.
For positive values of V’ 1361 , it is assumed that
a conventional display will apply a 2.5-power function
to produce display tristimulus values. A wide-gamut
display is expected to do whatever signal processing is
necessary to deliver the colors within its gamut.
The gamma-corrected R’G’B’ components of Rec. 1361
lie in the range [-0.25 … +1.152]. Their black-to-white
excursion is reduced by the ratio 160 ⁄219 from that of
Rec. 709, SMPTE 274M, or SMPTE 296M R’G’B’
components: Scaled by 160 for 8-bit coding, they
266 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES