CUT PRINT
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The Color of Digital
review by Ray Zone
Color and Mastering for Digital Cinema
Digital Cinema Industry Handbook Series
By Glenn Kennel
Focal Press
185 pps, casebound, $69.95
ISBN No. 0-240-80874-6
For several years now, motion picture editors have been on the leading edge of the emerging data-centric world of post-production. The coming of digital cinema is yet another indication of that evolution. Toward that end, Focal Press has commenced publishing a Digital Cinema Industry Handbook Series under series editor Charles Swartz that addresses fundamental technical issues of importance to all contemporary motion picture professionals.
In July 2005, the Digital Cinema Initiatives, LLC, a consortium formed by seven major Hollywood studios, in conjunction with the SMPTE DC28––a working group of technical experts from the studios––published a consensus technical specification for a 2K/4K scalable solution for digital cinema standards. Glenn Kennel, the author of this book, chaired the SMPTE DC28 ad hoc group on Color and helped draft several digital cinema standards. He is well qualified to address issues of digital dailies, previews, Digital Intermediate (DI), mastering and digital cinema packaging.
It is expected that digital distribution will take five to ten years to be fully deployed and, for the time being, color encoding standards for digital cinema must be fully compatible with 35mm film. The mastering process incorporates creative decisions about color that affect the look and feel of the picture. Kennel’s discussion of digital cinema color encoding covers the middle to the end of the process and does not address color calibration for image origination.
After providing a brief overview of color and mastering for digital cinema, Kennel addresses color on film, exposure of an image on color negative, and a description of the IP/IN release printing process. A chapter on “Color Space” reviews the basic characteristics of human vision followed by a discussion of contrast sensitivity in theatrical viewing conditions. Numerous color images, charts and graphs illustrate the complex concepts under discussion throughout the entire book. Kennel’s writing as well is clear and concise.
The importance of the Reference Projector and its environment in digital cinema mastering cannot be overstated. To ensure image consistency from screen to screen, colorimetric tolerances must be maintained. Since the environment of the mastering room, particularly ambient light, affects the quality of the projected image, DCI and SMPTE DC28 defined its minimum performance characteristics in SMPTE Recommended Practice (RP) 431.2. The RP was drafted to enable consistent quality in generating and reproducing digital cinema masters. Two levels of tolerances were specified, one for critical mastering and screening rooms and another, slightly wider, for reproduction in cinemas.
“The first step in the filmmaking process to embrace digital technology was editing,” observes Kennel. He characterizes both the upright Moviola and the flatbed KEM editing systems as “essentially miniature projectors with film transports.” Today, virtually all feature films are edited with non-linear digital systems and Kennel suggests that this technology has led to “a much faster paced, rapid-cutting style in many action films.” Visual effects (VFX) was the second filmmaking process to embrace digital technology, and with the development of CCD film scanners and CRT film recorders, the optical printer became obsolete.
Color grading for both film and digital cinema is today accomplished in a mastering room equipped with a 20-30 foot wide screen and digital cinema projector. The same digital master output to film for internegative (IN) release printing is easily converted into the Digital Cinema Distribution Master (DCDM). With most digital intermediate processes the print film characteristic is simply “baked in” in the form of the 3-D LUT (Look Up Table) that is used in the reference display.
The finished digital master is called the Digital Source Master (DSM) in the DCI specification. It is sent to an array of film recorders, such as an ArriLaser, for output to one or more inter-negatives for release printing. A 20-minute reel takes about 16 hours of continuous recording, at a rate of two seconds per frame.
Color encoding for digital cinema distribution is a process of color transforms converting the RGB mastering space to XYZ color encoding. SMPTE standards define reference projector metadata requirements to be used for downstream color gamut mapping. In the future, when wider color gamut digital projectors are introduced, backward compatibility with legacy projectors will be necessary.
Kennel worked for the Texas Instruments’ DLP Cinema group in 2004. With a separate chapter titled “DLP Cinema – A Case Study,” he describes the workings of this leading projection technology and its historical development in response to the needs of the motion picture industry. He also explains the color processing and calibration technology built into the DLP projector.
Discussions of digital displays, digital 3-D presentation and a look into the future round out this well-designed handbook. Despite the rapid evolution of digital imaging technology, Kennel’s handbook is likely to remain useful for some time to come.
Ray Zone can be contacted at r3dzone@earthlink.net.