Color and Mastering for Digital Cinema

Glenn Kennel

• Publisher: Routledge
• Year: 2012
• ISBN:
  9781136033377
• Edition: 1
• Topic: Languages & Linguistics
• Subtopic: Communication Studies
• Index: Languages & Linguistics

Color and Mastering for Digital Cinema explores the implications for motion picture post production processes and changes required to the supporting equipment and software. While a new concept to the motion picture community, the selection of the wide gamut, output-referred XYZ color space for digital cinema distribution is based on decades of color science and experience in other industries. The rationale for choosing XYZ and the other color encoding parameters is explained and the book also provides a full case study of the development of DLP Cinema® projectors by Texas Instruments. Finally, this book explores how the XYZ color encoding concept can be extended to support enhanced display technologies in the future.This book contains: * Brilliant 4-color illustrations that compliment the color science explanations * Never before published industry information from author Glenn Kennel, a world leader in digital cinema color technology * Descriptions of key issues and background on decisions that were made in the standardization processBy Glenn Kennel, Glenn Kennel is VP/GM of Feature Film Services at Laser Pacific Media Corporation, a leading provider of a full range of post production services for television and feature film. Recently, he worked for the DLP Cinema group of Texas Instruments in a role that included technology and business development. Previously, in a twenty year career with Kodak, he led the development of the Cineon digital film scanners and laser recorders and the prototype HDTV telecine that became the Spirit Datacine. As a consultant, he helped DCI draft the technical specifications for digital cinema. Kennel also chairs the SMPTE DC28 Color ad hoc group and the DC28.20 Distribution working group. He is a SMPTE Fellow and has received the SMPTE Journal Award. He is also a member of the Academy of Motion Picture Arts and Sciences.

1
Overview of Color and Mastering for Digital Cinema

In June of 1999, George Lucas released his film “Star Wars: Episode 1” on two digital cinema screens—one in New York and one in Los Angeles. In the five years since this historic debut, over 150 films have been released digitally to over 500 screens in 30 countries around the world. These digital movies have played over 20,000 shows to satisfied audiences. Although digital cinema has not been widely promoted as a new and improved display method, educated audiences have shown a preference for digital over film presentation.

This book presents a survey of the development of color encoding and decoding standards for digital cinema distribution and exhibition. It describes the key issues and provides background on decisions that were made in the standardization process. Although the author was a key participant in the development of the SMPTE¹ DC28 documents, it is recommended that the reader refer to the published SMPTE standards² for the final word on implementation.

This book refers to colorimetric principles that are more rigorously defined in color textbooks^3,4 and assumes that the reader has a working knowledge of basic color principles and motion picture industry practices. However, one does not need to be a color scientist or industry insider to read and understand this book.

In late 1999, SMPTE established the DC28 working group to study the standardization requirements for digital cinema distribution, with the goal of establishing a world-wide standard. Since its standardization by SMPTE in 1916, the 35 mm motion picture film format has served as the single worldwide distribution standard for movies. 35 mm motion picture film has weathered the test of time, supporting major exhibition enhancements like sound, color, widescreen presentation and multitrack digital soundtracks, all compatible with 35 mm projection equipment based on the original standard. In today’s hyper-competitive and fast-changing digital world, it seemed a tall order to establish a digital cinema distribution standard that would serve the industry for the next century. But the industry set its sights on just that. The goal was to develop a universal standard for digital cinema distribution that could be implemented in a cost effective way today, while also extensible to support future exhibition improvements.

The SMPTE DC28 group concluded its study work at the end of 2000 by identifying the need for standards for digital cinema mastering, distribution and exhibition. Working groups were established to address each of these areas. In addition, ad hoc groups of industry experts were formed to address specific issues, including packaging, key management and security, and color. The DC28 color ad hoc group began its work in 2002, focusing its initial discussions on the color encoding for digital cinema. The group was composed of experts from diverse parts of the industry that included studios, post production facilities and equipment manufacturers. While everyone agreed on the goal, there were many opinions on how best to get there.

While the SMPTE DC28 work proceeded slowly and steadily as a due process forum with diverse interests, the establishment in 2002 of the Digital Cinema Initiatives, LLC (DCI), a consortium formed by seven major Hollywood studios, provided a focus for the development of the digital cinema standards. A group of technical experts from the member studios met regularly to hammer out a consensus technical specification for digital cinema distribution. In its work, DCI used available and prototypical digital cinema equipment to evaluate requirements for compression, security, content packaging and color encoding. DCI hired several industry experts to supplement its internal expertise. Amongst other things, DCI funded the Contrast Sensitivity Test that verified the bit depth requirement for color encoding (see Chapter 4).

Most importantly, DCI provided a venue for the political process of building consensus amongst its members. Its crowning achievement was the delivery of a consensus technical specification for a 2 K/4 K scalable solution in July 2005 that was supported in its entirety by all of its members. This consensus specification removed a substantial uncertainty, paving the way for commercial deployment of compliant systems while substantially reducing the risk of technological obsolescence.

STUDIO OBJECTIVES

CTO Brad Hunt of the Motion Picture Association of America (MPAA) framed the work of DCI with the following ten goals:

1. ENHANCED THEATRICAL EXPERIENCE—The introduction of digital cinema must be used by the motion picture industry as an opportunity to significantly enhance the theatrical film experience and thus bring real benefits to theater audiences.

2. QUALITY—The picture and sound quality of digital cinema should present as accurately as possible the creative intent of the filmmaker. To that end, its quality must exceed the quality of a projected 35 mm “answer print” shown under optimum studio screening theater conditions. Any image compression that is used should be visually lossless.

3. WORLDWIDE COMPATIBILITY—The system should be based around global standards so that content can be distributed and played anywhere in the world as can be done today with a 35 mm film print.

4. OPEN STANDARDS—The components and technologies used should be based on open standards that foster competition amongst multiple vendors of equipment and services.

5. INTEROPERABLE—Each of the components of the system should be built around clearly defined standards and interfaces that insure interoperability between different equipment.

6. EXTENSIBLE—The hardware used in the system should be easily upgraded as advances in technology are made. This is especially important in evolving to higher quality levels.

7. SINGLE INVENTORY—Once a consensus on digital cinema standards is reached and implemented, upgrades to the system should be designed so that a single inventory of content can be distributed and compatibly played on all equipment installations.

8. TRANSPORT—The system should accommodate a variety of secure content transport mechanisms, including electronic as well as a physical media delivery.

9. SECURE CONTENT PROTECTION—The system must include a highly secure, end-to-end, conditional access content protection system, including digital rights management and content watermarking, because of the serious harm associated with the theft of digital content at this stage of its distribution life cycle. Playback devices must use on-line authentication with the decrypted content files never accessible in the clear.

10. REASONABLE COST—The system standards and mastering format(s) should be chosen so that the capital equipment and operational costs are reasonable. All required technology licenses should be available on reasonable and non-discriminatory terms.

The objectives that must be considered in the selection of color encoding standards for digital cinema distribution are an enhanced theatrical experience, with picture quality better than a film answer print⁵, and open standards that are interoperable and extensible. And all of this must be supported by equipment and operational costs that are reasonable. In addition, since the transition to digital distribution cannot happen overnight and will likely take 5 to 10 years, it is important that the mastering process and the end product be compatible with traditional 35 mm film distribution and exhibition practices.

This compatibility with 35 mm film locked down two major exhibition requirements: screen luminance and chromaticity. Creative color decisions that affect the look and feel of the picture are part of the mastering process. For the creative intent to be faithfully reproduced on the cinema screen, it is critical that the screen luminance and white point be standardized. And since movies will be exhibited on both film and digital projectors for some time, it is critical that these parameters be consistent in both venues. For compatibility with legacy film projectors, the digital cinema standards specify a screen luminance of 48 cd/m² (14 ft L) with a white point of 0.314 x, 0.351 y. The basis for these parameters will be explained in Chapter 5.

This treatment of digital cinema color encoding will describe the standards and practices that are used to create the digital cinema master, and those that are used to faithfully reproduce this master in cinema exhibition. Since this process does not include color calibration or color encoding for image origination, front-end production is excluded from this analysis. Instead, the book focuses on the middle to the end of the process, as shown by the highlighted blocks in Figure 1.1, and the color calibration and standards that support mastering and distribution. Origination, dailies, editing and preview functions are outside of the scope of this book. Color encoding for digital cinema distribution picks up in the digital mastering process (where the final color grading is performed on a calibrated reference projector). The complimentary process of color decoding is performed on a calibrated projector in the cinema.

Figure 1-1. Motion Picture Workflow.

Now, here’s a quick preview of the rest of the book.

Chapter 2, “Color in Film”, covers the color characteristics of the traditional motion picture film system, starting with the exposure of an image on a color negative film. The extended range of a typical negative film is described, along with typical placement of a white card and 18% gray for normal and over-exposures. The characteristics of color print film are then described, along with the “print-through” curves that result when a negative is printed onto print stock. The IP/IN release printing process is discussed.

Chapter 3, “Color Space”, starts with a review of the basic characteristics of human vision, and how color scientists have developed experimental methods to model it. After reviewing the requirements for the selection of a color space for digital cinema, the various options are summarized. The experimental basis for the CIE colorimetric analysis is reviewed, leading to the standard x, y, z color matching functions and the X, Y and Z color primaries.

Chapter 4, “Transfer Function”, covers the definition of the non-linear (gamma 1/2.6) encoding transfer function selected for digital cinema distribution. DCI conducted an experiment to verify that the Barten model for contrast sensitivity applies to theatrical viewing conditions, and the results of this test are described.

Chapter 5, “Reference Projector and Environment”, covers the definition of a reference projector for digital cinema mastering and exhibition, for the purpose of insuring consistency from screen to screen. The important image attributes are defined along with appropriate tolerances for mastering and exhibition. The calibration and measurement of digital cinema projectors is reviewed, with a brief description of the instrumentation and test patterns required.

Chapter 6, “Digital Mastering”, reviews the evolving trends in mastering, including the widespread adoption of a digital intermediate process that supports the digital conforming and grading of the full feature film, while supporting outputs to everything from film release prints, to digital cinema distribution masters (DCDMs) and home video masters. The workflow of the digital intermediate process is reviewed, along with the choices of working resolution (2 K or 4 K) and color calibration (film-centric or digital-centric).

Chapter 7, “Color Encoding for Digital Cinema Distribution”, describes the color transforms in converting from the RGB mastering space to XYZ color encoding. The rationale for the output-referred color encoding is reviewed. The draft SMPTE standards also include the definition of metadata from the reference projector to facilitate gamut mapping downstream.

Chapter 8, “Projector Color Processing”, covers the processing requirements for a digital cinema projector. Calibration is critical to provide consistency from screen to screen and over time. When wider gamut projectors are introduced in the future, a gamut mapping capability will need to be implemented in legacy projectors in order to maintain backward compatibility. Finally, the advantages of relative luminance encoding are reviewed in the context of a practical test.

Chapter 9, “DLP Cinema — A Case Study” describes how the leading digital cinema projection technology from Texas Instruments works, and its historical development in response to industry needs. This includes an explanation of the color processing and calibration technology built into DLP Cinema projectors.

, “Digital Display Technologies”, provides a brief overvi...

Table of contents

• Cover
• Halftitle
• Title
• Copyright
• Decdication
• Contents
• Preface
• Acknowledgements
• About the Author
• About the Series Editor
• 1. Overview of Color and Mastering for Digital Cinema
• 2. Color in Motion Picture Film
• 3. Color Space for Digital Cinema
• 4. Transfer Function
• 5. Reference Projector and Environment
• 6. Digital Mastering
• 7. Color Encoding forDigital Cinema Distribution
• 8. Color Processing in the Projector
• 9. DLP Cinema® Case Study
• 10. Digital Display Technologies
• 11. Digital 3D Presentation
• 12. The Future
• Index