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19.2/T. Matsumoto
19.2: xvYCC: A new standard for video systems using extended-gamut YCC
Color Space
Tatsuhiko Matsumoto, Yoshihide Shimpuku, Takehiro Nakatsue, Shuichi Haga, Hiroaki Eto,
Yoshiyuki Akiyama, Naoya Katoh
Sony Corporation, 6-7-35 Kitashinagawa Shinagawa-ku, Tokyo, 141-0001 Japan
Tel: +81-3-5448-3868 E-mail: Tatsuhiko.Matsumoto@jp.sony.com
Abstract
We have developed a new display / video camera and wide-
gamut characterizing tools for a new standard for extended-gamut
YCC color space called xvYCC. Video systems adapting this
standard will have improved accuracy of color reproduction of
real world.
1. Introduction
Various new kinds of wide-gamut displays are emerging. Wide-
gamut video systems are capable of brighter color video imaging
and of showing wide-gamut displays at their best. Using the wide-
gamut characterizing tools that we developed, the color
reproduction accuracy of real images was evaluated. The
definition of extended color space standard is the same as the
standard for inside the conventional sRGB gamut and maintains
downward compatibility with currently-used video signals. In
signal processing using the proposed standard, luminance and
chrominance is separately characterized in color space, so the
standard is suitable for image-data processing.
Most surface colors can be 55% expressed by sRGB but 100%
by xvYCC. The xvYCC standard was successfully applied to an
LCD-TV with LED or a wide-gamut CCFL backlight, a Laser
Display (GxL) and a video camera.
2. A wide-gamut color space for video
signal
The xvYCC standard is based on the implementation of YCC
color-space (ITU-R BT.709-5 for HDTV and ITU-R BT.605-5 for
SDTV) encoding and can transfer to a wider gamut of color space.
Table 2-1 shows xvYCC colorimetric parameters and related
characteristics.
The primary colors and reference white are identical to those of
ITU-R BT.709-5, which are from the standard sRGB CRT display
defined in IEC 61966-2-1. The new standard clearly defines the
currently-undefined signal regions. Figure 2-1 is a two–
dimensional color space schematic diagram of both the xvYCC
and the conventional standards. The ordinate shows luma and the
abscissa shows chroma. Inside the rhombus area is the color space
defined by the BT.709-5 standard. Extending the opto-electronic
transfer characteristics of xvYCC to negative value and over 1.0,
the color space is expanded into the rectangular area in Fig. 2-1.
As seen in the figure, the new standard extends the BT.709-5
standard 1 to 15 and 241 to 254 in the chroma axis and also
extends 1 to 15 and 236 to 254 in the luma axis. It is completely
same inside the gamut of the BT.709-5 standard. Consequently, it
retains the downward compatibility with widely used standard
video signals.
The new standard can be defined using n-bit quantization in
addition to conventional 8,10-bit quantization.
Figures 2-2 and 2-3 show a three-dimensional view of sRGB and
xvYCC in a lightness-chromaticity space. The contour of sRGB in
Fig.2-2 is expressed in a triangular pillar with white top. On the
other hand, the upper space of xvYCC has a hollowed top and the
lower space is spreading as shown in Fig.2-3. The Munsell Color
Cascade proposed by Prof. Michael R. Pointer is an index of 769
colors that expresses the surface color [Pointer, personal
communication]. The red dots in Fig.2-2 and Fig.2-3 are the each
color defined by the Munsell Color Cascade.
16
235
254
16
240
254
Y
Cb, Cr
1
-0.5 +0.5 +0.56
128
-0.57
Black
Over White
0 < R’,G’,B’ < 1
1< R’,G’,B’
R’,G’,B’< 0
(Gamut of BT.709-5)
Gamut of xvYCC
Extended
Extended Region
Extended Region
R’,G’,B’< 0
1< R’,G’,B’
Extended
BT.709-5
(sRGB)
sYCC
xvYCC
0.0
1.0
Luma
Chroma
(sRGB)
1
Figure 2-1. Two–dimensional color space schematic diagram
of xvYCC and BT.709-5
Figure 2-2. BT.709 gamut + Munsell Color Cascade
We evaluated the degree of coverage of the surface color on the
three dimensional views shown in Fig.2-2 and 2-3. 55% of colors
19.2/ T. Matsumoto
Table 2-1. xvYCC colorimetric parameters and related characteristics
xvYCC
601
xvYCC
709
Primary colours and reference
white
ITU-R BT.709-5 (IEC 61966-2-1 sRGB)
Red: x:0.640 0 y:0.330 0 z:0.030 0
Green: x:0.300 0 y:0.600 0 z:0.100 0
Blue: x:0.150 0 y:0.060 0 z:0.790 0
White/D65 x:0.312 7 y:0.329 0 z:0.358 3
Opto-electronic transfer
characteristics
Extended ITU-R BT.709-5
If R,G,B≤-0.018,
R’=-1.099x(-R)
0.45
+0.099
G’=-1.099x(-G)
0.45
+0.099
B’=-1.099x(-B)
0.45
+0.099
If -0.018<R,G,B<0.018
R’=4.50xR
G’=4.50xG
B’=4.50xB
If R,G,B≥0.018
R’=1.099xR
0.45
-0.099
G’=1.099xG
0.45
-0.099
B’=1.099xB
0.45
-0.099
YCC (luma-chroma-chroma)
encoding
ITU-R BT.601-5
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
−−
−−=
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
B'
G'
R'
3 0.0817 0.4180 0.500
0 0.5003 0.3317 0.168
0 0.1140 0.5870 0.299
Cr'
Cb'
Y'
601
601
601
ITU-R BT.709-5
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
−−
−−=
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
B'
G'
R'
8 0.0452 0.4540 0.500
0 0.5004 0.3856 0.114
2 0.0722 0.7156 0.212
Cr'
Cb'
Y'
709
709
709
Digital quantization
For 8-bit representation:
Y
xvYCC(8)
=round[219xY’+16]
Cb
xvYCC(8)
=round[224xCb’+128]
Cr
xvYCC(8)
=round[224xCr’+128]
For n-bit (n>8)representation:
Y
xvYCC(N)
=round[(219xY’+16)x2
n-8
]
Cb
xvYCC(N)
=round[(224xCb’+128) x2
n-8
]
Cr
xvYCC(N)
=round[(224xCr’+128) x2
n-8
]
Levels from 1 to 254 in the case of 8-bit encoding are available.
in the Munsell Color Cascade are found in the sRGB gamut and
the remaining 45% are on the outside, which means that about
half of the surface colors are not expressible as shown in Fig.2-2.
Figure 2-3 shows that all colors in the Munsell Color Cascade are
included in the three-dimensional view of the gamut of the
xvYCC standard.
Figure 2-3. xvYCC gamut + Munsell Color Cascade
3. Video Systems for xvYCC
We designed a camera and display system to be operated under
the xvYCC standard signal format. Figure 3-1 is a block diagram
of the system.
The camera system is designed for high saturated primary colors.
Color space conversion transfers the signal primary colors to the
sRGB primary colors while keeping the negative value of RGB
signal.
The opto-electronic transfer curve as defined by the xvYCC
standard is shown in Fig.3-2. The new curve extends above 1 in
the electronic-signal axis and is new below 0, where it is
symmetric at the origin. The extended gamut area uses the unused
area of the conventional YCC signal.
The display system should also keep the negative value of the
xvYCC RGB signal until the color space conversion in wide-
gamut displays such as wide-gamut CCFL LCD TVs, LED
Backlight LCD TVs, and GxL Laser Projectors.
19.2/T. Matsumoto
Figure 3-1. xvYCC Block Diagram
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
-0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
R,G,B
domain for BT.709,BT.601
domain for xvYCC
Opto Signal
Electronic Signal
Figure 3-2. Opto-electronic transfer curve
4. Tools to evaluate the xvYCC system
For evaluating the xvYCC system, the authors made the color
chart extending the GretagMacbeth ColorChecker, to evaluate the
xvYCC system. This extended color chart contains vivid colors
not included in the sRGB gamut.(Fig. 4-1)
We also developed the new xvYCC signal for the chart and the
ColorChecker.
Figure 4-1. xvYCC Color Chart
We shot xvYCC wide-gamut video contents. Figure 4-2-1 is a
sample of the clips we shot. Figure 4-2-2 is the captured image
from the RGB waveform monitor (Tektronix WFM-700M), which
shows that most of the green channel has a negative value. In the
waveform image, the spaces with a negative value show the
complementary color. This is why deep red of the roses can be so
vividly imaged.
Figure 4-2-1. xvYCC Video Clip
Figure 4-2-2. Waveform Image
Figure 4-2. Sample of the xvYCC wide gamut video contents
and its waveform
5. Improvement of the color reproduction
of TV sets
We measured the color differences between the xvYCC color
chart and the GretagMacbeth ColorChecker and these color
charts’ digital imaging on the xvYCC display. The results are
shown in Fig. 5-1. This figure clearly highlighted the difference of
the u’v’ values between the actual charts and those reproductions
on the xvYCC display. We also measured the color differences on
a conventional LCD display, as shown in Fig. 5-2. Compared with
the color differences between inside and outside the sRGB gamut,
∆Eab* outside the sRGB gamut on the xvYCC display is almost
as the same as that inside the sRGB gamut. On the other hand, the
color differences outside the sRGB gamut are larger than those
inside the sRGB gamut on the conventional LCD display. So, we
can conclude that the xvYCC system improves the color
reproduction accuracy of the extend gamut.
Wide
Gamut
CCD
Color
Space
Conversion
YCC
Encoding
xvYCC - camera
xvYCC-diaplay
YCC
Decoding
Colo
r
Space
Conversion
Wide
Gamut
display
Opto
-
Electronic
transfe
r
Inverse
Opto
-
Electronic
transfe
r
RGB- signal( Wi out Negative Value)th
signal(
RGB
- With Negative alue)V
YCbCr-
signal
xvYCC - Signal
19.2/ T. Matsumoto
Figure 5-1. Color differences on xvYCC display (LED
backlight LCD display)
○:reproductions on the display □:real color chart
Figure 5-2. Color differences on conventional LCD display
○:reproductions on the display □:real color chart
6. Conclusion
In the lightness-chromaticity diagram in Fig.2-3, xvYCC covers
most of the 100% surface color. Thanks to xvYCC for video
applications, the color gamut of the display and the camera have
been improved. Reducing the color differences in the wide gamut
makes it possible to reproduce video contents with vivid colors.
7. References
[1] IEC 61966-2-4 Multimedia systems and equipment - Colour
measurement and management - Part 2-4: Colour
management – Extended-gamut YCC colour space for video
applications – xvYCC (2006)
[2] RECOMMENDATION ITU-R BT.709-5 PARAMETER
VALUES FOR THE HDTV STANDARDS FOR
PRODUCTION AND INTERNATIONAL PROGRAMME
EXCHANGE (1990-1994-1995-1998-2000)
[3] IEC 61966-2-1:1999 Multimedia systems and equipment –
Colour measurement and management –Part 2-1: Colour
management – Default RGB colour space –sRGB Amendent
1 (2003)
[4] T. Matsumoto, "Displaying sYCC Still Images on a Wide-
Color-Gamut Television," IDW'04 pp1603-1606(2004)
[5] K. Kakinuma “The world first LCD TV featuring LED
backlight expands color space 1.5 times as conventional
TV,” Nikkei Electronics, Dec.20,pp. 123-130 (2004)
[6] M. R. Pointer, “The gamut of real surface colours,” Colour
Research and Applications, Vol.5, pp145-155(1980)
[7] J. Kumada and T. Nishizawa, “Reproducible Color Gamut of
Television Systems,” SMPTE Journal, August 1992(1992)
[8] N. Katoh, "Extended colour space for capturing devices,"
Proc. 10th Congress of the International Colour Association:
AIC Colour 05, Granada, Spain, pp. 647-652 (2005)
[9] H. Sugiura, “Six-Primary-Color 23-in WXGA LCD using
Six-Color LEDs,” SID 05 DIGEST pp. 1124-1127 (2005)
[10] T. Nakakatsue, ”Wide Gamut Display and Wide Gamut
Video Signal,” Color Forum Japan (2005)
[11] T. Nakakatsue, ”The xvYCC Wide Gamut Color Space for
Video Signal and The Status of Standardization,” FPD
International 2005(2005)