January 27, X’Y’Z’ Color Encoding for Digital Cinema Distribution Glenn Kennel HPA Technology Retreat January 27, 2005

2 SMPTE Color AHG Prinyar Boon Matt Cowan Chuck Harrison Jim Houston George Joblove Glenn Kennel Howard Lukk Tom Maier Arjun Ramamurthy Jeremy Selan John Silva Kaz Tsujikawa Brad Walker Ron Williams

3January 27, 2005 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

4January 27, 2005 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

5January 27, 2005 Planning for the Future Today’s Projectors Tomorrow’s Projectors IlluminationXenonLaser? Primaries3 3 or more? Color Gamut Similar to film Wider gamut Contrast2000:1 Higher contrast

6January 27, 2005 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 Based on international color standard Explicit device independence, extensibility, backward compatibility Explicit device independence, extensibility, backward compatibility Robust implementation, not dependent on metadata Robust implementation, not dependent on metadata

7January 27, 2005 ZX Y Visible colors Displayable colors Display Primaries XYZ encoding Space (triangle) Visible and XYZ

8January 27, 2005 Compress Encrypt Package Color grade Conform Store & Play Cinema Projector Mastering Projector Decompress Decrypt DSMDCP Color Encoding Color Management Color Decoding Calibrated Color 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 Workflow

January 27, Mastering Projector (Used in Content Creation or Color Grading)

10January 27, 2005 Mastering Projector Primaries Today, the projectors used in mastering are DLP Cinema TM projectors, with a color gamut expanded beyond CCIR 709 to more closely match film Encoding Primaries xyu’v’ R G B Note: x, y, u’,v’ refers to the chromaticity coordinates defined by the CIE.

11January 27, 2005 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

12January 27, 2005 Mastering Projector Peak White Existing digital cinema practice sets the peak white at 12 ftL (42 cd/m 2 ) DCI tests verified that film produces 14 ftL for peak whites (with 16 ftL open gate) Dmin samples from Technicolor and Deluxe Dmin samples from Technicolor and Deluxe Draft SMPTE standard recommends a peak white level of 14 ftL (48 cd/m 2 )

January 27, DCDM Color Encoding

14January 27, 2005 Color Encoding Parameters CIE XYZ Color Primaries Gamma 1/2.6 Transfer Function 12 bits per channel Metadata for downstream gamut mapping- describes color gamut that is used in the master “Encoding” White Point D E (1.0,1.0,1.0) is implicit with CIE XYZ D E (1.0,1.0,1.0) is implicit with CIE XYZ

15January 27, 2005 Color Encoding Primaries XYZ color primaries (1931 CIE standard) Device independent, colorimetric representation Device independent, colorimetric representation Encompasses full color gamut Encompasses full color gamut Luminance isolated to one component (Y) Luminance isolated to one component (Y) Encoding Primaries xyu’v’ X Y Z Note: x, y, u’,v’ refers to the chromaticity coordinates defined by the CIE.

16January 27, 2005 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 2.6 [ ] 1/ R’G’B’RGBXYZX’Y’Z’

17January 27, 2005 Encoding Transfer Function Where: CV is the resulting Code Value for a color component. L is the luminance output in cd/m 2 P is (extra headroom reserved for future white point changes to accommodate range from D55 to D65).

January 27, Color Decoding in the Cinema Projector

19January 27, 2005 Projector Transfer Function P is the peak luminance output (48 cd/m 2 )

20January 27, 2005 Projector Color Transform X’Y’Z’ color space of DCDM is converted to Projector (device specific) RGB color space with a linear matrix 2.6 [ ] 2.6 Light Modulators X’Y’Z’ XYZ RGB In this example, the decoding matrix is the inverse of the encoding matrix.

January 27, Color Processing for Digital Intermediate for both film and digital cinema distribution

22January 27, 2005 DI Option 1 Mastering Projector Color Corrections Conforming DSM RGB Printing Density Dual 292 R’G’B’ 12 bits 3D Print Film LUTs (for film matching) Scan Film or Import Digital Images DCDM Output to film (Laser Fim Recorder) Film IN Color Encoding To X’Y’Z’ 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’ 1 2

23January 27, 2005 DI Option 1b Mastering Projector Color Corrections Conforming DSM RGB Printing Density Dual 292 3D Print Film LUTs (for film matching) Scan Film or Import Digital Images DCDM Output to film (Laser Fim Recorder) Film IN Color Encoding To X’Y’Z’ 1 2 Put the 3D print film LUT inside the Mastering Projector- source and color- corrected 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’ Render 3D LUT Into DCDM

24January 27, 2005 DI Option 2 Mastering Projector Color Corrections Conforming DSM RGB Printing Density Dual 292 Scan Film or Import Digital Images DCDM Output to film (Laser Fim Recorder) Film IN Color Encoding To X’Y’Z’ 1 2 3D LUT to convert to RGB Printing Density Perform color corrections from source RGB Printing Density to color- corrected 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). Color-corrected R’G’B’ DCDM

25January 27, 2005 Creating Video Masters Video displays have a smaller color gamut (CCIR 709) Simple colorimetric conversion could result in clipping of out of gamut colors 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 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 Adjusting the transfer function for color appearance Applying a hue-preserving “soft-clip” for out of gamut colors 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

January 27, Conclusion

27January 27, 2005 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. Otherwise, the cinema projector may unveil unintended details or color errors in the blacks.

28January 27, 2005 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.

29January 27, 2005 X’Y’Z’ Conclusions and Next Steps Robust, device-independent output-referred color encoding definition Independent of display primaries and white point 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 Color transforms were independently verified by several companies Next step is to test color matching across different projection technologies 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

30January 27, 2005 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