Quest for an Image Interchange and Mastering Format HPA Technology Retreat February 23, 2006 Jim Houston © 2006 A.M.P.A.S. ®

Academy of Motion Picture Arts and Sciences Science and Technology Council Advanced Technology Programs File Format Committee

File Format Project Develop a new framework for managing image data, metadata, and color transformations

Current Problems non-standard RGB color spaces log/lin/gamma conversions more multi-facility productions ‘secret sauces’ for output and preview chasing calibration - variability of film developing many digital master versions unknown colorimetry from digital cameras

Future Needs Wide gamut displays High dynamic range 4K and greater pipelines Co-existing film and digital releases Accommodate future production techniques

Goals Preserve cinematographer intent Able to incorporate film-sourced material Apply uniform color management within pipelines Provide consistent color across facilities Eliminate image conversion errors Create known and fixed transforms for the most common use cases Preserve, and absorb, current workflows

Lessons from previous formats

Approach Define fixed color space – ( primaries and white point ) – fixed color encoding specification

Approach (cont) Use floating point color –16-bit half-floats 10 bit mantissa, 5 bit exponent, 1 sign bit –Nvidia/ILM format for OpenEXR provides 33+ stops range Negative numbers can represent out of gamut colors

Merge colorimetric and densitometric workflows Standardize calibration targets for film recording and scanning Model transforms with Reference Input Device and Reference Output Device Provide default viewing transform for ‘print- like’ behavior Approach (cont)

Master and Interchange Format Destination format for –color correctors –digital cameras –renderers –scanners –telecines Usable in as many parts of the digital workflow as possible, but allows facilities to keep using their own pipeline A common studio master for deliverables and facility interchange

Surrounding Issues Compression Real-time playback Look management software On-set Previews (DP intended filters for example) Monitor Previewing Laser Projectors Energy Linear Workflow (CGI) OpenEXR and DPX Workflow metadata Digital Dailies

Color Encoding Specification Colorimetric specification: Each code value maps to a specific color

Color Gamut Want a gamut that covers a large range of common colors, But how do we encode the densitometric film world…

Background on Cineon system Film intermediate system Scan negatives in, record out to internegative Print from either camera negative or I.N. looks the same Cineon used “printing density” to close the loop for input and output calibration

Printing Density RGB PD = StatusM to PD * (StatusM - Dmin) 500 * 10-bit range of code values from reference black (CV=95 usually set to Dmin of negative) reference white (CV=685 at about 90% reflective white)

Production workflows needing linear operations Rendering Compositing Color matrixing Color correction (lift, gain, gamma) Area operations (e.g. anti-aliasing, blurs)

Linearized Printing Density LPD = 10^ ( Printing Density / gamma) gamma is a constant (e.g. 0.60) LPD will likely have a straight-line center portion and may contain knee and shoulder roll-offs relative to scene exposures.

Benefits of L.P.D. Allows linear operations on image data facilitating visual effects pipeline In the right space for color matrix operations Conversion to DCDM X’Y’Z’ is easy Eliminates Log/Lin difficulties with use of a single reversible transform Cinematographer choices are preserved Image data interpretation is specified without need for ‘color space’ metadata

Input Methodology L.P.D. Color Encoding Reference Input Device Scene Reference Input Transform Tone curve is proportional to scene exposure but exact energy linear light is not assured We can accept inexactness because we have a WYSIWIG preview stage

Output Methodology L.P.D. Color Encoding Preview Output Transform Reference Rendering Transform Reference Device Transform Reference Display Device Display Device Output Color Appearance Device Gamut & Encoding

Viewing Methodology Provide a standard, default 3D LUT “a virtual print stock” The image encoding maintains wide-gamut and high-dynamic range information. Gamut mapping and range compression is part of the Device Output Transform. Theatrical viewing environments are assumed

What about OpenEXR? Examine use of Color Transformation Language (CTL) OpenEXR is closest format type to where we are heading Narrow some features of EXR (fewer codecs), and add new concepts Close cooperation with OpenEXR development team

Our Tasks Complete requirements definition Evaluate color space primaries Specify input and output calibration targets Create a preview ‘viewing LUT’ Develop an API spec Proof of concept test

Remaining Issues Reference implementation Intellectual property considerations Build consensus with potential users and vendors Engage a standards body (SMPTE)

Other Industry Efforts American Society of Cinematographers “Color Decision List’ (CDL) International Color Consortium Digital Motion Pictures Working Group SMPTE Digital Cinema Technology Committee (DC28) AdHoc Group on Colorimetry AdHoc Group for the uncompressed DCDM OpenEXR Development Team

Summary §Linearized Printing Density aids the integration of digital and film workflows §(Half) floating point provides wide gamut and wide dynamic range color encoding §A standardized color space with defined transforms reduces conversion errors §Multi-facility workflows are improved with a well-defined image framework §Allows for future growth and new technology on the horizon

Acknowledgements: Thanks to the 25 members of the File Format committee whose work is presented in this session. Presentation will be made available on HPA website. For comments on the talk, or submissions to the committee, contact © 2006 A.M.P.A.S. ®