January 27, 2005January 27, 2005 11

X’Y’Z’ Color EncodingX’Y’Z’ Color Encodingfor Digital Cinema Distributionfor Digital Cinema Distribution

Glenn KennelGlenn Kennel

HPA Technology RetreatHPA Technology RetreatJanuary 27, 2005 January 27, 2005

22January 27, 2005January 27, 2005

SMPTE Color AHGSMPTE Color AHG

Prinyar BoonPrinyar Boon

Matt CowanMatt Cowan

Chuck HarrisonChuck Harrison

Jim HoustonJim Houston

George JobloveGeorge Joblove

Glenn KennelGlenn Kennel

Howard LukkHoward Lukk

Tom Maier Tom Maier

Arjun RamamurthyArjun Ramamurthy

Jeremy SelanJeremy Selan

John SilvaJohn Silva

Kaz TsujikawaKaz Tsujikawa

Brad WalkerBrad Walker

Ron WilliamsRon Williams

33January 27, 2005January 27, 2005

Color Image EncodingColor Image Encoding

Choosing a Color Space for the DCDMChoosing a Color Space for the DCDM

Why X’Y’Z’?Why X’Y’Z’?

Color in the Overall WorkflowColor in the Overall Workflow

Color Encoding and DecodingColor Encoding and Decoding

Digital Intermediate WorkflowDigital Intermediate Workflow

Video MastersVideo Masters

ConclusionsConclusions

44January 27, 2005January 27, 2005

Basic Requirements for Basic Requirements for DCDM Color EncodingDCDM Color Encoding

One master shall play on all projectors and One master shall play on all projectors and look the same (device independent)look the same (device independent)Open standard with no licensing feesOpen standard with no licensing feesExtensible to wider color gamut and wider Extensible to wider color gamut and wider contrast in future projectorscontrast in future projectorsFuture masters shall be backward Future masters shall be backward compatible with today’s projectorscompatible with today’s projectorsCan be implemented in today’s mastering Can be implemented in today’s mastering environmentenvironment

55January 27, 2005January 27, 2005

Planning for the FuturePlanning for the Future

Today’s Today’s ProjectorsProjectors

Tomorrow’s Tomorrow’s ProjectorsProjectors

IlluminationIllumination XenonXenon Laser?Laser?

PrimariesPrimaries 33 3 or more?3 or more?

Color GamutColor Gamut Similar to filmSimilar to film Wider gamutWider gamut

ContrastContrast 2000:12000:1 Higher contrastHigher contrast

66January 27, 2005January 27, 2005

Color Space Options ConsideredColor Space Options Considered

R’G’B’R’G’B’ using extended gamut DLP primaries with using extended gamut DLP primaries with Xenon light sourceXenon light source

Parametric R’G’B’-Parametric R’G’B’- R’G’B’ with metadata to R’G’B’ with metadata to define color primaries of Reference Projectordefine color primaries of Reference Projector

Wide gamut R’G’B’Wide gamut R’G’B’ using CIE 1931 XYZ color using CIE 1931 XYZ color primaries- hereby called primaries- hereby called X’Y’Z’X’Y’Z’ Based on international color standardBased on international color standard Explicit device independence, extensibility, backward Explicit device independence, extensibility, backward

compatibility compatibility Robust implementation, not dependent on metadataRobust implementation, not dependent on metadata

77January 27, 2005January 27, 2005 Z X

Y

Visible colors

Displayablecolors

DisplayPrimaries

XYZ encodingSpace (triangle)

Visible and XYZ

88January 27, 2005January 27, 2005

CompressEncryptPackage

Color gradeConform

Store &Play

CinemaProjector

MasteringProjector

DecompressDecrypt

DSM DCPColor

Encoding

Color Management

Color Decoding

CalibratedColor Ref Projector

gamut metadata

DCDM(X’Y’Z’)

DSM:

Digital Source Master

DCP:

Digital Cinema Package

DCDM:

Digital Cinema Distribution Master

Color in the Overall WorkflowColor in the Overall Workflow

January 27, 2005January 27, 2005 99

Mastering ProjectorMastering Projector

(Used in Content Creation (Used in Content Creation or Color Grading)or Color Grading)

1010January 27, 2005January 27, 2005

Mastering Projector PrimariesMastering Projector Primaries

Today, the projectors used in mastering are DLP Today, the projectors used in mastering are DLP CinemaCinemaTMTM projectors, with a color gamut expanded projectors, with a color gamut expanded beyond CCIR 709 to more closely match film beyond CCIR 709 to more closely match film

Encoding Encoding PrimariesPrimaries xx yy u’u’ v’v’

RR 0.68000.6800 0.32000.3200 0.496350.49635 0.525550.52555

GG 0.26500.2650 0.69000.6900 0.098600.09860 0.577670.57767

BB 0.15000.1500 0.06000.0600 0.175440.17544 0.157890.15789

Note: x, y, u’ ,v’ refers to the chromaticity coordinates defined by the CIE.

1111January 27, 2005January 27, 2005

Mastering Projector White PointMastering Projector White Point

Although white point is independent of color encoding,Although white point is independent of color encoding,

A consistent white point target (and tolerances) for A consistent white point target (and tolerances) for mastering and cinema projectors is importantmastering and cinema projectors is important

Considering the installed base of Xenon projectors, we Considering the installed base of Xenon projectors, we recommend a recommend a calibratedcalibrated white point of (0.314, 0.351)white point of (0.314, 0.351), , CCT 6300KCCT 6300K

0.3100

0.3200

0.3300

0.3400

0.3500

0.3600

0.2950 0.3050 0.3150 0.3250 0.3350 0.3450

x

y Daylight curve

D61

DLP

DLP Tolerances

6100

7000

5100

0.314 0.351

Daylight curve

1212January 27, 2005January 27, 2005

Mastering Projector Peak WhiteMastering Projector Peak White

Existing digital cinema practice sets the Existing digital cinema practice sets the peak white at 12 ftL (42 cd/mpeak white at 12 ftL (42 cd/m22))

DCI tests verified that film produces 14 ftL DCI tests verified that film produces 14 ftL for peak whites (with 16 ftL open gate)for peak whites (with 16 ftL open gate) Dmin samples from Technicolor and DeluxeDmin samples from Technicolor and Deluxe

Draft SMPTE standard recommends a Draft SMPTE standard recommends a peak white level of peak white level of 14 ftL (48 cd/m14 ftL (48 cd/m22))

January 27, 2005January 27, 2005 1313

DCDM Color EncodingDCDM Color Encoding

1414January 27, 2005January 27, 2005

Color Encoding ParametersColor Encoding Parameters

CIE XYZ Color PrimariesCIE XYZ Color Primaries

Gamma 1/2.6 Transfer FunctionGamma 1/2.6 Transfer Function

12 bits per channel12 bits per channel

Metadata for downstream gamut mapping- Metadata for downstream gamut mapping- describes color gamut that is used in the describes color gamut that is used in the master master

““Encoding” White PointEncoding” White Point DDEE (1.0,1.0,1.0) is implicit with CIE XYZ (1.0,1.0,1.0) is implicit with CIE XYZ

1515January 27, 2005January 27, 2005

Color Encoding PrimariesColor Encoding Primaries

XYZ color primaries XYZ color primaries (1931 CIE standard)(1931 CIE standard) Device independent, colorimetric representationDevice independent, colorimetric representation Encompasses full color gamutEncompasses full color gamut Luminance isolated to one component (Y)Luminance isolated to one component (Y)

EncodingEncodingPrimariesPrimaries xx yy u’u’ v’v’

XX 1.00001.0000 0.00000.0000 4.00004.0000 0.00000.0000

YY 0.00000.0000 1.00001.0000 0.00000.0000 0.60000.6000

ZZ 0.00000.0000 0.0000.000 0.00000.0000 0.00000.0000

Note: x, y, u’ ,v’ refers to the chromaticity coordinates defined by the CIE.

1616January 27, 2005January 27, 2005

Encoding Color TransformEncoding Color Transform

R’G’B’ color space of Reference Projector is converted R’G’B’ color space of Reference Projector is converted to device-independent X’Y’Z’ color space of DCDM with to device-independent X’Y’Z’ color space of DCDM with a linear space matrixa linear space matrix

DLP

DLP

DLP

B

G

R

Z

Y

X

9074.00471.00000.0

0689.07216.02095.0

1723.02771.04452.0

2.6[ ]

1/2.6

2.6

R’G’B’ RGB XYZ X’Y’Z’

1717January 27, 2005January 27, 2005

Encoding Transfer FunctionEncoding Transfer Function

6.2

1

*4095

P

LCV

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).

January 27, 2005January 27, 2005 1818

Color DecodingColor Decodingin the Cinema Projectorin the Cinema Projector

1919January 27, 2005January 27, 2005

Projector Transfer FunctionProjector Transfer Function

P is the peak luminance output (48 cd/m2)

12-bit code valueOutput

Luminance, cd/m2Relative

Luminance Notes4095 48.000 100.000% Peak White3686 36.511 76.065%3276 26.870 55.980%2866 18.980 39.542%2457 12.718 26.497%2048 7.922 16.504%1771 5.429 11.311% 18% Gray1638 4.432 9.233%1228 2.096 4.366%737 0.556 1.158%410 0.121 0.252%288 0.048 0.101% Black 1000:1220 0.024 0.050% Black 2000:1168 0.012 0.025% Black 4000:1118 0.005 0.010% Black 10,000:1

6.2

4095*

CV

PL

Projector Transfer Function

0

8

16

24

32

40

48

0 512 1024 1536 2048 2560 3072 3584 4096

Code Value

Lu

min

ance

(cd

/m2)

2020January 27, 2005January 27, 2005

Projector Color TransformProjector Color Transform

X’Y’Z’ color space of DCDM is converted to Projector X’Y’Z’ color space of DCDM is converted to Projector (device specific) RGB color space with a linear matrix(device specific) RGB color space with a linear matrix

Z

Y

X

B

G

R

DLP

DLP

DLP

1009.10876.00412.0

0226.06897.17952.0

4402.00180.12.7254

2.6[ ]

2.6 Light

ModulatorsX’Y’Z’ XYZ RGB

In this example, the decoding matrix is the inverse of the encoding matrix.

January 27, 2005January 27, 2005 2121

Color Processing forColor Processing forDigital IntermediateDigital Intermediate

for both film and digital cinema distributionfor both film and digital cinema distribution

2222January 27, 2005January 27, 2005

DI Option 1DI Option 1

MasteringProjector

Color CorrectionsConforming

DSMRGB Printing Density

Dual 292 R’G’B’ 12 bits

3D Print Film LUTs(for film matching)

Scan Film orImport Digital Images

DCDM

Output to film(Laser Fim Recorder) Film IN

Color EncodingTo X’Y’Z’

Use a 3D LUT in color corrector or external box to mimic film print stock, Use a 3D LUT in color corrector or external box to mimic film print stock, starting with Printing Density source imagesstarting with Printing Density source images

1 1 - Color-corrected master is ready for film output (Printing Density)- Color-corrected master is ready for film output (Printing Density)2 2 - Render (“bake in”) the film LUT when outputting the DCDM; - Render (“bake in”) the film LUT when outputting the DCDM;

Encode color to X’Y’Z’Encode color to X’Y’Z’

1

2

2323January 27, 2005January 27, 2005

DI Option 1bDI Option 1b

MasteringProjector

Color CorrectionsConforming

DSMRGB Printing Density

Dual 292

3D Print Film LUTs(for film matching)

Scan Film orImport Digital Images

DCDM

Output to film(Laser Fim Recorder) Film IN

Color EncodingTo X’Y’Z’

1

2

Put the 3D print film LUT Put the 3D print film LUT inside the Mastering Projectorinside the Mastering Projector- source and color-- source and color-corrected images are Printing Densitycorrected images are Printing Density

1 1 - Color-corrected master is ready for film output (Printing Density)- Color-corrected master is ready for film output (Printing Density)2 2 - Render (“bake in”) the film LUT when outputting the DCDM; - Render (“bake in”) the film LUT when outputting the DCDM;

Encode color to X’Y’Z’Encode color to X’Y’Z’

Render 3D LUTInto DCDM

2424January 27, 2005January 27, 2005

DI Option 2DI Option 2

MasteringProjector

Color CorrectionsConforming

DSMRGB Printing Density

Dual 292

Scan Film orImport Digital Images

DCDM

Output to film(Laser Fim Recorder)

Film IN

Color EncodingTo X’Y’Z’1

2 3D LUT to convert toRGB Printing Density

Perform color corrections from source RGB Printing Density to color-Perform color corrections from source RGB Printing Density to color-corrected R’G’B’ DCDM.corrected R’G’B’ DCDM.

1 1 - Color-corrected images are ready for color encoding to X’Y’Z’.- Color-corrected images are ready for color encoding to X’Y’Z’.2 2 - Use an - Use an (inverse) 3D LUT(inverse) 3D LUT to convert from R’G’B’ DCDM to RGB to convert from R’G’B’ DCDM to RGB

Printing Density in a 2nd pass (for film output).Printing Density in a 2nd pass (for film output).

Color-correctedR’G’B’ DCDM

2525January 27, 2005January 27, 2005

Creating Video MastersCreating Video Masters

Video displays have a smaller color gamut (CCIR 709)Video displays have a smaller color gamut (CCIR 709) Simple colorimetric conversion could result in clipping of out of Simple colorimetric conversion could result in clipping of out of

gamut colorsgamut colors Viewing conditions are also very different; pictures look different Viewing conditions are also very different; pictures look different

on a small display in a dim (10%) surroundon a small display in a dim (10%) surround

In theory, a 3D LUT can be built to convert to CCIR 709 In theory, a 3D LUT can be built to convert to CCIR 709 color gamut, preserving the look of the picturecolor gamut, preserving the look of the picture

Adjusting the transfer function for color appearanceAdjusting the transfer function for color appearance Applying a hue-preserving “soft-clip” for out of gamut colorsApplying a hue-preserving “soft-clip” for out of gamut colors

A trim pass is still necessary to tune color aesthetics and A trim pass is still necessary to tune color aesthetics and frame (pan/scan) the picture for the 4:3 full-frame video frame (pan/scan) the picture for the 4:3 full-frame video versionversion

January 27, 2005January 27, 2005 2626

ConclusionConclusion

2727January 27, 2005January 27, 2005

The Reference ProjectorThe Reference Projector

X’Y’Z’ encoding (as used here) is output-referredX’Y’Z’ encoding (as used here) is output-referredFaithful color reproduction depends on Faithful color reproduction depends on careful careful calibrationcalibration of the mastering projector and cinema of the mastering projector and cinema projectorsprojectorsThe environment is also critical (screen quality, The environment is also critical (screen quality, port glass and ambient light must be controlled)port glass and ambient light must be controlled)The Mastering Projector must have the The Mastering Projector must have the best best available blackavailable black level (sequential contrast) level (sequential contrast) Otherwise, the cinema projector may unveil Otherwise, the cinema projector may unveil

unintended details or color errors in the blacks.unintended details or color errors in the blacks.

2828January 27, 2005January 27, 2005

Color Management inColor Management inthe Mastering Processthe Mastering Process

Proprietary color processing (3D LUTs or Proprietary color processing (3D LUTs or otherwise) used to match print film or otherwise) used to match print film or create a unique look may be included in create a unique look may be included in the Mastering Projector, butthe Mastering Projector, butThis proprietary color processing must be This proprietary color processing must be rendered into the DCDM.rendered into the DCDM.Better to put these LUTs in the color Better to put these LUTs in the color corrector or in an external box or software corrector or in an external box or software process.process.

2929January 27, 2005January 27, 2005

X’Y’Z’ Conclusions and Next StepsX’Y’Z’ Conclusions and Next Steps

Robust, device-independent output-referred Robust, device-independent output-referred color encoding definitioncolor encoding definition Independent of display primaries and white pointIndependent of display primaries and white point

Supports future improvements in color gamut Supports future improvements in color gamut and contrast ratioand contrast ratioDCI StEM test provided a proof of conceptDCI StEM test provided a proof of concept Color transforms were independently verified by Color transforms were independently verified by

several companiesseveral companies Next step is to test color matching across different Next step is to test color matching across different

projection technologiesprojection technologies

Color correctors should implement R’G’B’ to Color correctors should implement R’G’B’ to X’Y’Z’ color conversion for DCDM outputX’Y’Z’ color conversion for DCDM output

3030January 27, 2005January 27, 2005

Additional ReferencesAdditional References

Swartz, editor, “Understanding Digital Cinema”Swartz, editor, “Understanding Digital Cinema”

Cowan, et al, Journal SMPTE, September 2004, Cowan, et al, Journal SMPTE, September 2004, “Contrast Sensitivity Experiment to Determine “Contrast Sensitivity Experiment to Determine the Bit Depth for Digital Cinema”the Bit Depth for Digital Cinema”

Draft SMPTE Standard for DCDMDraft SMPTE Standard for DCDM

Draft SMPTE RP for Reference Projector and Draft SMPTE RP for Reference Projector and EnvironmentEnvironment

Draft SMPTE EG for Color ProcessingDraft SMPTE EG for Color Processing