X’Y’Z’ Color Encoding
for Digital Cinema Distribution
Glenn Kennel
HPA Technology Retreat
January 27, 2005
January 27, 2005
1
SMPTE Color AHG
Prinyar Boon
Matt Cowan
Chuck Harrison
Jim Houston
George Joblove
Glenn Kennel
Howard Lukk
January 27, 2005
Tom Maier
Arjun Ramamurthy
Jeremy Selan
John Silva
Kaz Tsujikawa
Brad Walker
Ron Williams
2
Color Image Encoding
Choosing a Color Space for the DCDM
Why X’Y’Z’?
Color in the Overall Workflow
Color Encoding and Decoding
Digital Intermediate Workflow
Video Masters
Conclusions
January 27, 2005
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Basic Requirements for
DCDM Color Encoding
One master shall play on all projectors and
look the same (device independent)
Open standard with no licensing fees
Extensible to wider color gamut and wider
contrast in future projectors
Future masters shall be backward
compatible with today’s projectors
Can be implemented in today’s mastering
environment
January 27, 2005
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Planning for the Future
Illumination
Today’s
Projectors
Xenon
Tomorrow’s
Projectors
Laser?
Primaries
3
3 or more?
Color Gamut
Similar to film
Wider gamut
Contrast
2000:1
Higher contrast
January 27, 2005
5
Color Space Options Considered
R’G’B’ using extended gamut DLP primaries with
Xenon light source
Parametric R’G’B’- R’G’B’ with metadata to
define color primaries of Reference Projector
Wide gamut R’G’B’ using CIE 1931 XYZ color
primaries- hereby called X’Y’Z’



Based on international color standard
Explicit device independence, extensibility, backward
compatibility
Robust implementation, not dependent on metadata
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Visible
and XYZ
Y
Visible colors
Display
Primaries
Displayable
colors
XYZ encoding
Space (triangle)
January 27, 2005
Z
7
X
Color in the Overall Workflow
Cinema
Projector
DCDM:
Mastering
Projector
Calibrated
Color
DSM
Color grade
Conform
Color
Management
Digital Cinema
Distribution Master
Color
Decoding
Ref Projector
gamut
metadata
Color
Encoding
Decompress
Decrypt
DCDM
(X’Y’Z’)
Compress
Encrypt
Package
DCP
Store &
Play
DSM:
DCP:
Digital Source Master
Digital Cinema Package
January 27, 2005
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Mastering Projector
(Used in Content Creation
or Color Grading)
January 27, 2005
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Mastering Projector Primaries
Today, the projectors used in mastering are DLP
CinemaTM projectors, with a color gamut expanded
beyond CCIR 709 to more closely match film
Encoding
Primaries
x
y
u’
v’
R
0.6800
0.3200
0.49635
0.52555
G
0.2650
0.6900
0.09860
0.57767
B
0.1500
0.0600
0.17544
0.15789
Note: x, y, u’ ,v’ refers to the chromaticity coordinates defined by the CIE.
January 27, 2005
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Mastering Projector White Point
Although white point is independent of color encoding,
A consistent white point target (and tolerances) for
mastering and cinema projectors is important
Considering the installed base of Xenon projectors, we
recommend a calibrated white point of (0.314, 0.351),
CCT 6300K
0.3600
5100
0.314 0.351
0.3500
Daylight curve
0.3400
y
Daylight curve
6100
D61
0.3300
DLP
DLP Tolerances
0.3200
7000
0.3100
0.2950
January 27, 2005
0.3050
0.3150
0.3250
x
0.3350
0.3450
11
Mastering Projector Peak White
Existing digital cinema practice sets the
peak white at 12 ftL (42 cd/m2)
DCI tests verified that film produces 14 ftL
for peak whites (with 16 ftL open gate)

Dmin samples from Technicolor and Deluxe
Draft SMPTE standard recommends a
peak white level of 14 ftL (48 cd/m2)
January 27, 2005
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DCDM Color Encoding
January 27, 2005
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Color Encoding Parameters
CIE XYZ Color Primaries
Gamma 1/2.6 Transfer Function
12 bits per channel
Metadata for downstream gamut mappingdescribes color gamut that is used in the
master
“Encoding” White Point

DE (1.0,1.0,1.0) is implicit with CIE XYZ
January 27, 2005
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Color Encoding Primaries
XYZ color primaries (1931 CIE standard)



Device independent, colorimetric representation
Encompasses full color gamut
Luminance isolated to one component (Y)
Encoding
Primaries
x
y
u’
v’
X
1.0000
0.0000
4.0000
0.0000
Y
0.0000
1.0000
0.0000
0.6000
Z
0.0000
0.000
0.0000
0.0000
Note: x, y, u’ ,v’ refers to the chromaticity coordinates defined by the CIE.
January 27, 2005
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Encoding Color Transform
R’G’B’ color space of Reference Projector is converted
to device-independent X’Y’Z’ color space of DCDM with
a linear space matrix
R’G’B’
2.6
2.6
RGB
[ ]
XYZ
1/2.6
X’Y’Z’
 X  0.4452 0.2771 0.1723  RDLP 
Y   0.2095 0.7216 0.0689  GDLP 
  
 

 Z  0.0000 0.0471 0.9074  BDLP 
January 27, 2005
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Encoding Transfer Function
L
CV  4095 *  
P
1
2.6
Where:
CV is the resulting Code Value for a color component.
L is the luminance output in cd/m2
P is 52.39 (extra headroom reserved for future white point changes to
accommodate range from D55 to D65).
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Color Decoding
in the Cinema Projector
January 27, 2005
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Projector Transfer Function
 CV 
L  P *

 4095 
January 27, 2005
Relative
Luminance
100.000%
76.065%
55.980%
39.542%
26.497%
16.504%
11.311%
9.233%
4.366%
1.158%
0.252%
0.101%
0.050%
0.025%
0.010%
Projector Transfer Function
Notes
Peak White
48
40
18% Gray
Luminance (cd/m2)
Output
12-bit code value Luminance, cd/m2
4095
48.000
3686
36.511
3276
26.870
2866
18.980
2457
12.718
2048
7.922
1771
5.429
1638
4.432
1228
2.096
737
0.556
410
0.121
288
0.048
220
0.024
168
0.012
118
0.005
2.6
32
24
16
8
Black
Black
Black
Black
1000:1
2000:1
4000:1
10,000:1
0
0
512
1024
1536
2048
2560
3072
3584
4096
Code Value
19
Projector Color Transform
X’Y’Z’ color space of DCDM is converted to Projector
(device specific) RGB color space with a linear matrix
X’Y’Z’
2.6
2.6
[ ]
XYZ
RGB
Light
Modulators
 RDLP   2.7254  1.0180  0.4402  X 
GDLP    0.7952 1.6897  0.0226  Y 

 
  
 BDLP   0.0412  0.0876 1.1009   Z 
In this example, the decoding matrix is the inverse of the encoding matrix.
January 27, 2005
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Color Processing for
Digital Intermediate
for both film and digital cinema distribution
January 27, 2005
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DI Option 1
Use a 3D LUT in color corrector or external box to mimic film print stock,
starting with Printing Density source images
1 - Color-corrected master is ready for film output (Printing Density)
2 - Render (“bake in”) the film LUT when outputting the DCDM;
Encode color to X’Y’Z’
Mastering
Projector
Dual 292
R’G’B’ 12 bits
3D Print Film LUTs
(for film matching)
Scan Film or
Import Digital Images
January 27, 2005
Color Corrections
Conforming
DSM
RGB Printing Density
2
1
Color Encoding
To X’Y’Z’
DCDM
Output to film
(Laser Fim Recorder)
Film IN
22
DI Option 1b
Put the 3D print film LUT inside the Mastering Projector- source and colorcorrected images are Printing Density
1 - Color-corrected master is ready for film output (Printing Density)
2 - Render (“bake in”) the film LUT when outputting the DCDM;
Encode color to X’Y’Z’
Mastering
Projector
3D Print Film LUTs
(for film matching)
Dual 292
Scan Film or
Import Digital Images
January 27, 2005
Color Corrections
Conforming
DSM
RGB Printing Density
Color Encoding
To X’Y’Z’
2
1
DCDM
Render 3D LUT
Into DCDM
Output to film
(Laser Fim Recorder)
Film IN
23
DI Option 2
Perform color corrections from source RGB Printing Density to colorcorrected R’G’B’ DCDM.
1 - Color-corrected images are ready for color encoding to X’Y’Z’.
2 - Use an (inverse) 3D LUT to convert from R’G’B’ DCDM to RGB
Printing Density in a 2nd pass (for film output).
Mastering
Projector
Dual 292
1
Color Encoding
To X’Y’Z’
2
3D LUT to convert to
RGB Printing Density
DCDM
Color-corrected
R’G’B’ DCDM
Scan Film or
Import Digital Images
January 27, 2005
Color Corrections
Conforming
DSM
RGB Printing Density
Output to film
(Laser Fim Recorder)
Film IN
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Creating Video Masters
Video displays have a smaller color gamut (CCIR 709)


Simple colorimetric conversion could result in clipping of out of
gamut colors
Viewing conditions are also very different; pictures look different
on a small display in a dim (10%) surround
In theory, a 3D LUT can be built to convert to CCIR 709
color gamut, preserving the look of the picture


Adjusting the transfer function for color appearance
Applying a hue-preserving “soft-clip” for out of gamut colors
A trim pass is still necessary to tune color aesthetics and
frame (pan/scan) the picture for the 4:3 full-frame video
version
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Conclusion
January 27, 2005
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The Reference Projector
X’Y’Z’ encoding (as used here) is output-referred
Faithful color reproduction depends on careful
calibration of the mastering projector and
cinema projectors
The environment is also critical (screen quality,
port glass and ambient light must be controlled)
The Mastering Projector must have the best
available black level (sequential contrast)

Otherwise, the cinema projector may unveil
unintended details or color errors in the blacks.
January 27, 2005
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Color Management in
the Mastering Process
Proprietary color processing (3D LUTs or
otherwise) used to match print film or
create a unique look may be included in
the Mastering Projector, but
This proprietary color processing must be
rendered into the DCDM.
Better to put these LUTs in the color
corrector or in an external box or software
process.
January 27, 2005
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X’Y’Z’ Conclusions and Next Steps
Robust, device-independent output-referred
color encoding definition

Independent of display primaries and white point
Supports future improvements in color gamut
and contrast ratio
DCI StEM test provided a proof of concept


Color transforms were independently verified by
several companies
Next step is to test color matching across different
projection technologies
Color correctors should implement R’G’B’ to
X’Y’Z’ color conversion for DCDM output
January 27, 2005
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Additional References
Swartz, editor, “Understanding Digital Cinema”
Cowan, et al, Journal SMPTE, September 2004,
“Contrast Sensitivity Experiment to Determine
the Bit Depth for Digital Cinema”
Draft SMPTE Standard for DCDM
Draft SMPTE RP for Reference Projector and
Environment
Draft SMPTE EG for Color Processing
January 27, 2005
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