DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Concerning Pointer, see the
marginal note on page 255.
Eq 26.8
C BC R components for Rec. 1361 HDTV
One method of extending the color gamut of an R’G’B’
system is to allow components to excurse below zero
and above unity. In Rec. 1361 transfer function, on
page 265, I explained one approach. Rec. 1361 is based
upon Rec. 709 primaries, but enables the RGB tristimulus
components to excurse from - 1 ⁄4 to + 4 ⁄3 .
When transformed to Rec. 709 Y’C B C R , all of the real
surface colors documented by Pointer – that is, all the
colors in Pointer’s gamut – produce values that are
Y’C BC R-valid. Though Rec. 1361 was needed to specify
the R’G’B’ representation of wide-gamut colors, no
special provisions are necessary to carry those colors
across a 709 Y’C BC Rinterface. The notation “Rec. 1361
Y’C B C R ,” or as I write it, 1361Y’C B C R , makes it explicit
that codewords outside the unit R’G’B’ cube are to be
interpreted as wide-gamut colors, instead of being
treated as RGB-illegal.
Equipment conforming to Rec. 1361 is not yet
deployed, and is not anticipated for several years.
Wide-gamut acquisition and production equipment will
begin to replace film over the next decade or so;
however, wide-gamut consumer displays are not
expected in that time frame. When these begin to be
deployed, it is unlikely that they will all have the same
gamut; electronics associated with each display will
have to process the color signals according to the properties
of each display. In the long term, gamut mapping
strategies comparable to those in the desktop color
management community will have to be deployed.
Y’CBCR from studio RGB
In studio equipment, 8-bit R’G’B’ components usually
use the same 219 excursion as the luma component of
Y’CBCR. To encode Y’CBCR from R’G’B’ in the range
[0…219] using 8-bit binary arithmetic, scale the
encoding matrix of Equation 26.6 by 256 ⁄219:
⎡709
219Y’
⎤ ⎡ 16 ⎤ ⎡ 54. 426 183. 091 18. 483⎤
⎡ 219R’
⎤
⎢ ⎥ ⎢ ⎥ 1 ⎢
⎥ ⎢ ⎥
⎢ CB
⎥ =
⎢
128
⎥
+ 30.000 100. 922 130. 922 219G’
⎢
256 ⎢
− −
⎥
•
⎢ ⎥
C
⎥
R 128 130. 922 118. 918 12. 005 219B’
⎣⎢
⎦⎥
⎣
⎢
⎦
⎥
⎣
⎢ − − ⎦
⎥
⎣
⎢
⎦
⎥
318 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES