Preface

[Just as] other information should be available to those who want to learn and understand, program source code is the only means for programmers to learn the art from their predecessors. It would be unthinkable for playwrights not to allow other playwrights to read their plays [or to allow them] at theater performances where they would be barred even from taking notes. Likewise, any good author is well read, as every child who learns to write will read hundreds of times more than it writes. Programmers, however, are expected to invent the alphabet and learn to write long novels all on their own. Programming cannot grow and learn unless the next generation of programmers has access to the knowledge and information gathered by other programmers before them. —Erik Naggum

Rendering is a fundamental component of computer graphics. At the highest level of abstraction, rendering is the process of converting a description of a three-dimensional scene into an image. Algorithms for animation, geometric modeling, texturing, and other areas of computer graphics all must pass their results through some sort of rendering process so that they can be made visible in an image. Rendering has become ubiquitous; from movies to games and beyond, it has opened new frontiers for creative expression, entertainment, and visualization.

In the early years of the field, research in rendering focused on solving fundamental problems such as determining which objects are visible from a given viewpoint. As effective solutions to these problems have been found and as richer and more realistic scene descriptions have become available thanks to continued progress in other areas of graphics, modern rendering has grown to include ideas from a broad range of disciplines, including physics and astrophysics, astronomy, biology, psychology and the study of perception, and pure and applied mathematics. The interdisciplinary nature of rendering is one of the reasons that it is such a fascinating area of study.

This book presents a selection of modern rendering algorithms through the documented source code for a complete rendering system. Nearly all of the images in this book, including the one on the front cover, were rendered by this software. All of the algorithms that came together to generate these images are described in these pages. The system, pbrt, is written using a programming methodology called literate programming that mixes prose describing the system with the source code that implements it. We believe that the literate programming approach is a valuable way to introduce ideas in computer graphics and computer science in general. Often, some of the subtleties of an algorithm can be unclear or hidden until it is implemented, so seeing an actual implementation is a good way to acquire a solid understanding of that algorithm’s details. Indeed, we believe that deep understanding of a number of carefully selected algorithms in this manner provides a better foundation for further study of computer graphics than does superficial understanding of many.

In addition to clarifying how an algorithm is implemented in practice, presenting these algorithms in the context of a complete and nontrivial software system also allows us to address issues in the design and implementation of medium-sized rendering systems. The design of a rendering system’s basic abstractions and interfaces has substantial implications for both the elegance of the implementation and the ability to extend it later, yet the trade-offs in this design space are rarely discussed.

pbrt and the contents of this book focus exclusively on photorealistic rendering, which can be defined variously as the task of generating images that are indistinguishable from those that a camera would capture in a photograph or as the task of generating images that evoke the same response from a human observer as looking at the actual scene. There are many reasons to focus on photorealism. Photorealistic images are crucial for special effects in movies because computer-generated imagery must often be mixed seamlessly with footage of the real world. In applications like computer games where all of the imagery is synthetic, photorealism is an effective tool for making the observer forget that he or she is looking at an environment that does not actually exist. Finally, photorealism gives a reasonably well-defined metric for evaluating the quality of the rendering system’s output.

Audience

There are three main audiences that this book is intended for. The first is students in graduate or upper-level undergraduate computer graphics classes. This book assumes existing knowledge of computer graphics at the level of an introductory college-level course, although certain key concepts such as basic vector geometry and transformations will be reviewed here. For students who do not have experience with programs that have tens of thousands of lines of source code, the literate programming style gives a gentle introduction to this complexity. We pay special attention to explaining the reasoning behind some of the key interfaces and abstractions in the system in order to give these readers a sense of why the system is structured in the way that it is.

The second audience is advanced graduate students and researchers in computer graphics. For those doing research in rendering, the book provides a broad introduction to the area, and the pbrt source code provides a foundation that can be useful to build upon (or at least to use bits of source code from). For those working in other areas of computer graphics, we believe that having a thorough understanding of rendering can be helpful context to carry along.

Our final audience is software developers in industry. Although many of the basic ideas in this book will be familiar to this audience, seeing explanations of the algorithms presented in the literate style may lead to new perspectives. pbrt also includes carefully crafted and debugged implementations of many algorithms that can be challenging to implement correctly; these should be of particular interest to experienced practitioners in rendering. We hope that delving into one particular organization of a complete and nontrivial rendering system will also be thought provoking to this audience.

Overview and Goals

pbrt is based on the ray-tracing algorithm. Ray tracing is an elegant technique that has its origins in lens making; Carl Friedrich Gauß traced rays through lenses by hand in the 19th century. Ray-tracing algorithms on computers follow the path of infinitesimal rays of light through the scene until they intersect a surface. This approach gives a simple method for finding the first visible object as seen from any particular position and direction and is the basis for many rendering algorithms.

pbrt was designed and implemented with three main goals in mind: it should be complete, it should be illustrative, and it should be physically based.

Completeness implies that the system should not lack key features found in high-quality commercial rendering systems. In particular, it means that important practical issues, such as antialiasing, robustness, numerical precision, and the ability to efficiently render complex scenes should all be addressed thoroughly. It is important to consider these issues from the start of the system’s design, since these features can have subtle implications for all components of the system and can be quite difficult to retrofit into the system at a later stage of implementation.

Our second goal means that we tried to choose algorithms, data structures, and rendering techniques with care and with an eye toward readability and clarity. Since their implementations will be examined by more readers than is the case for other rendering systems, we tried to select the most elegant algorithms that we were aware of and implement them as well as possible. This goal also required that the system be small enough for a single person to understand completely. We have implemented pbrt using an extensible architecture, with the core of the system implemented in terms of a set of carefully designed interface classes, and as much of the specific functionality as possible in implementations of these interfaces. The result is that one does not need to understand all of the specific implementations in order to understand the basic structure of the system. This makes it easier to delve deeply into parts of interest and skip others, without losing sight of how the overall system fits together.

There is a tension between the two goals of being complete and being illustrative. Implementing and describing every possible useful technique would not only make this book unacceptably long, but would also make the system prohibitively complex for most readers. In cases where pbrt lacks a particularly useful feature, we have attempted to design the architecture so that the feature could be added without altering the overall system design.

The basic foundations for physically based rendering are the laws of physics and their mathematical expression. pbrt was designed to use the correct physical units and concepts for the quantities it computes and the algorithms it implements. pbrt strives to compute images that are physically correct; they accurately reflect the lighting as it would be in a real-world version of the scene. One advantage of the decision to use a physical basis is that it gives a concrete standard of program correctness: for simple scenes, where the expected result can be computed in closed form, if pbrt does not compute the same result, we know there must be a bug in the implementation. Similarly, if different physically based lighting algorithms in pbrt give different results for the same scene, or if pbrt does not give the same results as another physically based renderer, there is certainly an error in one of them. Finally, we believe that this physically based approach to rendering is valuable because it is rigorous. When it is not clear how a particular computation should be performed, physics gives an answer that guarantees a consistent result.

Efficiency was given lower priority than these three goals. Since rendering systems often run for many minutes or hours in the course of generating an image, efficiency is clearly important. However, we have mostly confined ourselves to algorithmic efficiency rather than low-level code optimization. In some cases, obvious micro-optimizations take a backseat to clear, well-organized code, although we did make some effort to optimize the parts of the system where most of the computation occurs.

In the course of presenting pbrt and discussing its implementation, we hope to convey some hard-learned lessons from years of rendering research and development. There is more to writing a good renderer than stringing together a set of fast algorithms; making the system both flexible and robust is a difficult task. The system’s performance must degrade gracefully as more geometry or light sources are added to it or as any other axis of complexity is stressed.

The rewards for developing a system that addresses all these issues are enormous—it is a great pleasure to write a new renderer or add a new feature to an existing renderer and use it to create an image that could not be generated before. Our most fundamental goal in writing this book was to bring this opportunity to a wider audience. Readers are encouraged to use the system to render the example scenes in the pbrt software distribution as they progress through the book. Exercises at the end of each chapter suggest modifications to the system that will help clarify its inner workings and more complex projects to extend the system by adding new features.

The website for this book is located at pbrt.org. This site includes links to the pbrt source code, scenes that can be downloaded to render with pbrt, and a bug tracker, as well as errata. Any errors in this text that are not listed in the errata can be reported to the email address [email protected]. We greatly value your feedback!

Changes Between The First and Second Editions

Six years passed between the publication of the first edition of this book in 2004 and the second edition in 2010. In that time, thousands of copies of the book were sold, and the pbrt software was downloaded thousands of times from the book’s website. The pbrt user base gave us a significant amount of feedback and encouragement, and our experience with the system guided many of the decisions we made in making changes between the version of pbrt presented in the first edition and the version in the second edition. In addition to a number of bug fixes, we also made several significant design changes and enhancements:

Removal of the plugin architecture: The first version of pbrt used a runtime plugin architecture to dynamically load code for implementations of objects like shapes, lights, integrators, cameras, and other objects that were used in the scene currently being rendered. This approach allowed users to extend pbrt with new object types (e.g., new shape primitives) without recompiling the entire rendering system. This approach initially seemed elegant, but it complicated the task of supporting pbrt on multiple platforms and it made debugging more difficult. The only new usage scenario that it truly enabled (binary-only distributions of pbrt or binary plugins) was actually contrary to our pedagogical and open-source goals. Therefore, the plugin architecture was dropped in this edition.
Removal of the image-processing pipeline: The first version of pbrt provided a tone-mapping interface that converted high-dynamic-range (HDR) floating-point output images directly into low-dynamic-range TIFFs for display. This functionality made sense in 2004, as support for HDR images was still sparse. In 2010, however, advances in digital photography had made HDR images commonplace. Although the theory and practice of tone mapping are elegant and worth learning, we decided to focus the new book exclusively on the process of image formation and skip the topic of image display. Interested readers should consult the book written by Reinhard et al. (2010) for a thorough and modern treatment of the HDR image display process.
Task parallelism: Multicore architectures became ubiquitous, and we felt that pbrt would not remain relevant without the ability to scale to the number of locally available cores. We also hoped that the parallel programming implementation details documented in this book would help graphics programmers understand some of the subtleties and complexities in writing scalable parallel code.
Appropriateness for “production” rendering: The first version of pbrt was intended exclusively as a pedagogical tool and a stepping-stone for rendering research. Indeed, we made a number of decisions in preparing the first edition that were contrary to use in a production environment, such as limited support for image-based lighting, no support for motion blur, and a photon mapping implementation that was not robust in the presence of complex lighting. With much improved support for these features as well as support for subsurface scattering and Metropolis light transport, we feel that with the second edition, pbrt became much more suitable for rendering very high-quality images of complex environments.

Changes Between The Second and Third Editions

With the passage of another six years, it was time to update and extend the book and the pbrt system. We continued to learn from readers’ and users’ experiences to better understand which topics were most useful to cover. Further, rendering research continued apace; many parts of the book were due for an update to reflect current best practices. We made significant improvements on a number of fronts:

Bidirectional light transport: The third version of pbrt added a bidirectional path tracer, including full support for volumetric light transport and multiple importance sampling to weight paths. An all-new Metropolis light transport integrator used components of the bidirectional path tracer, allowing for a particularly succinct implementation of that algorithm.
Subsurface scattering: The appearance of many objects—notably, skin and translucent objects—is a result of subsurface light transport. Our implementation of subsurface scattering in the second edition reflected the state of the art in the early 2000s; we thoroughly updated both BSSRDF models and our subsurface light transport algorithms to reflect the progress made in ten subsequent years of research.
Numerically robust intersections: The effects of floating-point round-off error in geometric ray intersection calculations have been a long-standing challenge in ray tracing: they can cause small errors to be present throughout the image. We focused on this issue and derived conservative (but tight) bounds of this error, which made our implementation more robust to this issue than previous rendering systems.
Participating media representation: We significantly improved the way that scattering media are described and represented in the system; this allows for more accurate results with nested scattering media. A new sampling technique enabled unbiased rendering of heterogeneous media in a way that cleanly integrated with all of the other parts of the system.
Measured materials: This edition added a new technique to represent and evaluate measured materials using a sparse frequency-space basis. This approach is convenient because it allows for exact importance sampling, which was not possible with the representation used in the previous edition.
Photon mapping: A significant step forward for photon mapping algorithms has been the development of variants that do not require storing all of the photons in memory. We replaced pbrt’s photon mapping algorithm with an implementation based on stochastic progressive photon mapping, which efficiently renders many difficult light transport effects.
Sample generation algorithms: The distribution of sample values used for numerical integration in rendering algorithms can have a surprisingly large effect on the quality of the final results. We thoroughly updated our treatment of this topic, covering new approaches and efficient implementation techniques in more depth than before.

Many other parts of the system were improved and updated to reflect progress in the field: microfacet reflection models were treated in more depth, with much better sampling techniques; a new “curve” shape was added for modeling hair and other fine geometry; and a new camera model that simulates realistic lens systems was made available. Throughout the book, we made numerous smaller changes to more clearly explain and illustrate the key concepts in physically based rendering systems like pbrt.

Changes Between The Third and Fourth Editions

Innovation in rendering algorithms has shown no sign of slowing down, and so in 2019 we began focused work on a fourth edition of the text. Not only does almost every chapter include substantial additions, but we have updated the order of chapters and ideas introduced, bringing Monte Carlo integration and the basic ideas of path tracing to the fore rather than saving them for the end.

Capabilities of the system that have seen especially significant improvements include:

Volumetric scattering: We have updated the algorithms that model scattering from participating media to the state of the art, adding support for emissive volumes, efficient sampling of volumes with varying densities, and robust support for chromatic media, where the scattering properties vary by wavelength.
Spectral rendering: We have excised all use of RGB color for lighting calculations; pbrt now performs lighting calculations exclusively in terms of samples of wavelength-dependent spectral distributions. Not only is this approach more physically accurate than using RGB, but it also allows pbrt to accurately model effects like dispersion.
Reflection models: Our coverage of the foundations of BSDFs and reflection models has been extensively revised, and we have expanded the range of BSDFs covered to include one that accurately models reflection from hair and another that models scattering from layered materials. The measured BRDF follows a new approach that can represent a wide set of materials’ reflection spectra.
Light sampling: Not only have we improved the algorithms for sampling points on individual light sources to better reflect the state of the art, but this edition also includes support for many-light sampling, which makes it possible to efficiently render scenes with thousands or millions of light sources by carefully sampling just a few of them.
GPU rendering: This version of pbrt adds support for rendering on GPUs, which can provide 10–100 times higher ray tracing performance than CPUs. We have implemented this capability in a way so that almost all of the code presented in the book runs on both CPUs and GPUs, which has made it possible to localize discussion of GPU-related issues to Chapter 15.

The system has seen numerous other improvements and additions, including a new bilinear patch shape, many updates to the sample-generation algorithms that are at the heart of Monte Carlo integration, support for outputting auxiliary information at each pixel about the visible surface geometry and reflection properties, and many more small improvements to the system.

Acknowledgments

Pat Hanrahan has contributed to this book in more ways than we could hope to acknowledge; we owe a profound debt to him. He tirelessly argued for clean interfaces and finding the right abstractions to use throughout the system, and his understanding of and approach to rendering deeply influenced its design. His willingness to use pbrt and this manuscript in his rendering course at Stanford was enormously helpful, particularly in the early years of its life when it was still in very rough form; his feedback throughout this process has been crucial for bringing the text to its current state. Finally, the group of people that Pat helped assemble at the Stanford Graphics Lab, and the open environment that he fostered, made for an exciting, stimulating, and fertile environment. Matt and Greg both feel extremely privileged to have been there.

We owe a debt of gratitude to the many students who used early drafts of this book in courses at Stanford and the University of Virginia between 1999 and 2004. These students provided an enormous amount of feedback about the book and pbrt. The teaching assistants for these courses deserve special mention: Tim Purcell, Mike Cammarano, Ian Buck, and Ren Ng at Stanford, and Nolan Goodnight at Virginia. A number of students in those classes gave particularly valuable feedback and sent bug reports and bug fixes; we would especially like to thank Evan Parker and Phil Beatty. A draft of the manuscript of this book was used in classes taught by Bill Mark and Don Fussell at the University of Texas, Austin, and Raghu Machiraju at Ohio State University; their feedback was invaluable, and we are grateful for their adventurousness in incorporating this system into their courses, even while it was still being edited and revised.

Matt Pharr would like to acknowledge colleagues and co-workers in rendering-related endeavors who have been a great source of education and who have substantially influenced his approach to writing renderers and his understanding of the field. Particular thanks go to Craig Kolb, who provided a cornerstone of Matt’s early computer graphics education through the freely available source code to the rayshade ray-tracing system, and Eric Veach, who has also been generous with his time and expertise. Thanks also to Doug Shult and Stan Eisenstat for formative lessons in mathematics and computer science during high school and college, respectively, and most important to Matt’s parents, for the education they have provided and continued encouragement along the way. Finally, thanks to NVIDIA for supporting the preparation of both the first and this latest edition of the book; at NVIDIA, thanks to Nick Triantos and Jayant Kolhe for their support through the final stages of the preparation of the first edition and thanks to Aaron Lefohn, David Luebke, and Bill Dally for their support of work on the fourth edition.

Greg Humphreys is very grateful to all the professors and TAs who tolerated him when he was an undergraduate at Princeton. Many people encouraged his interest in graphics, specifically Michael Cohen, David Dobkin, Adam Finkelstein, Michael Cox, Gordon Stoll, Patrick Min, and Dan Wallach. Doug Clark, Steve Lyon, and Andy Wolfe also supervised various independent research boondoggles without even laughing once. Once, in a group meeting about a year-long robotics project, Steve Lyon became exasperated and yelled, “Stop telling me why it can’t be done, and figure out how to do it!”—an impromptu lesson that will never be forgotten. Eric Ristad fired Greg as a summer research assistant after his freshman year (before the summer even began), pawning him off on an unsuspecting Pat Hanrahan and beginning an advising relationship that would span 10 years and both coasts. Finally, Dave Hanson taught Greg that literate programming was a great way to work and that computer programming can be a beautiful and subtle art form.

Wenzel Jakob was excited when the first edition of pbrt arrived in his mail during his undergraduate studies in 2004. Needless to say, this had a lasting effect on his career—thus Wenzel would like to begin by thanking his co-authors for inviting him to become a part of the third and fourth editions of this book. Wenzel is extremely indebted to Steve Marschner, who was his Ph.D. advisor during a fulfilling five years at Cornell University. Steve brought him into the world of research and remains a continuous source of inspiration. Wenzel is also thankful for the guidance and stimulating research environment created by the other members of the graphics group, including Kavita Bala, Doug James, and Bruce Walter. Wenzel spent a wonderful postdoc with Olga Sorkine Hornung, who introduced him to geometry processing. Olga’s support for Wenzel’s involvement in the third edition of this book is deeply appreciated.

We would especially like to thank the reviewers who read drafts in their entirety; all had insightful and constructive feedback about the manuscript at various stages of its progress. For providing feedback on both the first and second editions of the book, thanks to Ian Ashdown, Per Christensen, Doug Epps, Dan Goldman, Eric Haines, Erik Reinhard, Pete Shirley, Peter-Pike Sloan, Greg Ward, and a host of anonymous reviewers. For the second edition, thanks to Janne Kontkanen, Bill Mark, Nelson Max, and Eric Tabellion. For the fourth edition, we are grateful to Thomas Müller and Per Christensen, who both offered extensive feedback that has measurably improved the final version.

Many experts have kindly explained subtleties in their work to us and guided us to best practices. For the first and second editions, we are also grateful to Don Mitchell, for his help with understanding some of the details of sampling and reconstruction; Thomas Kollig and Alexander Keller, for explaining the finer points of low-discrepancy sampling; Christer Ericson, who had a number of suggestions for improving our kd-tree implementation; and Christophe Hery and Eugene d’Eon for helping us with the nuances of subsurface scattering.

For the third edition, we would especially like to thank Leo Grünschloß for reviewing our sampling chapter; Alexander Keller for suggestions about topics for that chapter; Eric Heitz for extensive help with details of microfacets and reviewing our text on that topic; Thiago Ize for thoroughly reviewing the text on floating-point error; Tom van Bussel for reporting a number of errors in our BSSRDF code; Ralf Habel for reviewing our BSSRDF text; and Toshiya Hachisuka and Anton Kaplanyan for extensive review and comments about our light transport chapters.

For the fourth edition, thanks to Alejandro Conty Estevez for reviewing our treatment of many-light sampling; Eugene d’Eon, Bailey Miller, and Jan Novák for comments on the volumetric scattering chapters; Eric Haines, Simon Kallweit, Martin Stich, and Carsten Wächter for reviewing the chapter on GPU rendering; Karl Li for feedback on a number of chapters; Tzu-Mao Li for his review of our discussion of inverse and differentiable rendering; Fabrice Rousselle for feedback on machine learning and rendering; and Gurprit Singh for comments on our discussion of Fourier analysis of Monte Carlo integration. We also appreciate extensive comments and suggestions from Jeppe Revall Frisvad on pbrt’s treatment of reflection models in previous editions.

For improvements to pbrt’s implementation in this edition, thanks to Pierre Moreau for his efforts in debugging pbrt’s GPU support on Windows and to Jim Price, who not only found and fixed numerous bugs in the early release of pbrt’s source code, but who also contributed a better representation of chromatic volumetric media than our original implementation. We are also very appreciative of Anders Langlands and Luca Fascione of Weta Digital for providing an implementation of their PhysLight system, which has been incorporated into pbrt’s PixelSensor class and light source implementations.

Many people have reported errors in the text of previous editions or bugs in pbrt. We’d especially like to thank Solomon Boulos, Stephen Chenney, Per Christensen, John Danks, Mike Day, Kevin Egan, Volodymyr Kachurovskyi, Kostya Smolenskiy, Ke Xu, and Arek Zimny, who have been especially prolific.

For their suggestions and bug reports, we would also like to thank Rachit Agrawal, Frederick Akalin, Thomas de Bodt, Mark Bolstad, Brian Budge, Jonathon Cai, Bryan Catanzaro, Tzu-Chieh Chang, Mark Colbert, Yunjian Ding, Tao Du, Marcos Fajardo, Shaohua Fan, Luca Fascione, Etienne Ferrier, Nigel Fisher, Jeppe Revall Frisvad, Robert G. Graf, Asbjørn Heid, Steve Hill, Wei-Feng Huang, John “Spike” Hughes, Keith Jeffery, Greg Johnson, Aaron Karp, Andrew Kensler, Alan King, Donald Knuth, Martin Kraus, Chris Kulla, Murat Kurt, Larry Lai, Morgan McGuire, Craig McNaughton, Don Mitchell, Swaminathan Narayanan, Anders Nilsson, Jens Olsson, Vincent Pegoraro, Srinath Ravichandiran, Andy Selle, Sébastien Speierer, Nils Thuerey, Eric Veach, Ingo Wald, Zejian Wang, Xiong Wei, Wei-Wei Xu, Tizian Zeltner, and Matthias Zwicker. Finally, we would like to thank the LuxRender developers and the LuxRender community, particularly Terrence Vergauwen, Jean-Philippe Grimaldi, and Asbjørn Heid; it has been a delight to see the rendering system they have built from pbrt’s foundation, and we have learned from reading their source code and implementations of new rendering algorithms.

Special thanks to Martin Preston and Steph Bruning from Framestore for their help with our being able to use a frame from Gravity (image courtesy of Warner Bros. and Framestore), and to Weta Digital for their help with the frame from Alita: Battle Angel (© 2018 Twentieth Century Fox Film Corporation, All Rights Reserved).

Production

For the production of the first edition, we would also like to thank our editor Tim Cox for his willingness to take on this slightly unorthodox project and for both his direction and patience throughout the process. We are very grateful to Elisabeth Beller (project manager), who went well beyond the call of duty for the book; her ability to keep this complex project in control and on schedule was remarkable, and we particularly thank her for the measurable impact she had on the quality of the final result. Thanks also to Rick Camp (editorial assistant) for his many contributions along the way. Paul Anagnostopoulos and Jacqui Scarlott at Windfall Software did the book’s composition; their ability to take the authors’ homebrew literate programming file format and turn it into high-quality final output while also juggling the multiple unusual types of indexing we asked for is greatly appreciated. Thanks also to Ken DellaPenta (copyeditor) and Jennifer McClain (proofreader), as well as to Max Spector at Chen Design (text and cover designer) and Steve Rath (indexer).

For the second edition, we would like to thank Greg Chalson, who talked us into expanding and updating the book; Greg also ensured that Paul Anagnostopoulos at Windfall Software would again do the book’s composition. We would like to thank Paul again for his efforts in working with this book’s production complexity. Finally, we would also like to thank Todd Green, Paul Gottehrer, and Heather Scherer at Elsevier.

For the third edition, we would like to thank Todd Green, who oversaw that go-round, and Amy Invernizzi, who kept the train on the rails throughout that process. We were delighted to have Paul Anagnostopoulos at Windfall Software part of this process for a third time; his efforts have been critical to the book’s high production value, which is so important to us.

The fourth edition saw us moving to MIT Press; many thanks to Elizabeth Swayze for her enthusiasm for bringing us on board, guidance through the production process, and ensuring that Paul Anagnostopoulos would again handle composition. Our deepest thanks to Paul for coming back for one more edition with us, and many thanks as well to MaryEllen Oliver for her superb work on copyediting and proofreading.

The Online Edition

As of November 1, 2023, the full text of the fourth edition is available online for free. Many thanks to MIT Press and Elizabeth Swayze for their support of a freely-available version of the book.

A number of open source systems have been instrumental to the development of the online version of Physically Based Rendering. We’d specifically like to thank the developers of Bootstrap, JERI, MathJax, and JQuery. We’d also like to thank Impallari Type for the design of the Domine font that we use for body text; Christian Robertson for the design of the Roboto Mono font that we use for code; and the designers of the Font Awesome fonts.

We’d also like to thank everyone who supported the earlier online edition through Patreon; as of 1 November 2023: 3Dscan, Abdelhakim Deneche, Alain Galvan, Andréa Machizaud, Aras Pranckevicius, Arman Uguray, Ben Bass, Claudia Doppioslash, Dong Feng, Enrico, Filip Strugar, Haralambi Todorov, Jaewon Jung, Jan Walter, Jendrik Illner, Jim Price, Joakim Dahl, Jonathan Stone, KrotanHill, Laura Reznikov, Malte Nawroth, Mauricio Vives, Mrinal Deo, Nathan Vegdahl, Pavel Panchekha, Pratool Gadtaula, Saad Ahmed, Scott Pilet, Shin Watanabe, Steve Watts Kennedy, Tom Hulton-Harrop, Torgrim Boe Skaarsmoen, William Newhall, Yining Karl Li, and Yury Mikhaylov. We have, however, closed the Patreon with the launch of the fourth edition.

Although the book is posted online for anyone to read for free, the text of the book remains © Copyright 2004–2023 Matt Pharr, Wenzel Jakob, and Greg Humphreys under a CC BY-NC-ND 4.0 license. The book figures are licensed with a CC BY-NC-SA 4.0 license with the thought that they may be useful when teaching graphics courses.

Scenes, Models, and Data

Many people and organizations have generously provided scenes and models for use in this book and the pbrt distribution. Their generosity has been invaluable in helping us create interesting example images throughout the text.

We are most grateful to Guillermo M. Leal Llaguno of Evolución Visual, www.evvisual.com, who modeled and rendered the iconic San Miguel scene that was featured on the cover of the second edition and is still used in numerous figures in the book. We would also especially like to thank Marko Dabrovic (www.3lhd.com) and Mihovil Odak at RNA Studios (www.rna.hr), who supplied a bounty of models and scenes used in earlier editions of the book, including the Sponza atrium, the Sibenik cathedral, and the Audi TT car model that can be seen in Figure 16.1 of this edition. Many thanks are also due to Florent Boyer, who provided the contemporary house scene used in some of the images in Chapter chap:bidir-methods.

We sincerely thank Jan-Walter Schliep, Burak Kahraman, and Timm Dapper of Laubwerk (www.laubwerk.com) for creating the Countryside landscape scene that was on the cover of the previous edition of the book and is used in numerous figures in this edition.

Many thanks to Angelo Ferretti of Lucydreams (www.lucydreams.it) for licensing the Watercolor and Kroken scenes, which have provided a wonderful cover image for this edition, material for numerous figures, and a pair of complex scenes that exercise pbrt’s capabilities.

Jim Price kindly provided a number of scenes featuring interesting volumetric media; those have measurably improved the figures for that topic. Thanks also to Beeple for making the Zero Day and Transparent Machines scenes available under a permissive license and to Martin Lubich for the Austrian Imperial Crown model. Finally, our deepest thanks to Walt Disney Animation Studios for making the production-complexity Moana Island scene available as well as providing the detailed volumetric cloud model.

The bunny, Buddha, and dragon models are courtesy of the Stanford Computer Graphics Laboratory’s scanning repository. The “killeroo” model is included with permission of Phil Dench and Martin Rezard (3D scan and digital representations by headus, design and clay sculpt by Rezard). The dragon model scan used in Chapter 9 is courtesy of Christian Schüller, and our thanks to Yasutoshi Mori for the material orb and the sports car model. The glass used to illustrate caustics in Chapter chap:bidir-methods is thanks to Simon Wendsche. The head model used to illustrate subsurface scattering was made available by Infinite Realities, Inc. under a Creative Commons Attribution 3.0 license. Thanks also to “tyrant monkey” for the BMW M6 car model and “Wig42” for the breakfast table scene; both were posted to blendswap.com, also under a Creative Commons Attribution 3.0 license.

We have made use of numerous environment maps from the PolyHaven website (polyhaven.com) for HDR lighting in various scenes; all are available under a Creative Commons CC0 license. Thanks to Sergej Majboroda and Greg Zaal, whose environment maps we have used.

Marc Ellens provided spectral data for a variety of light sources, and the spectral RGB measurement data for a variety of displays is courtesy of Tom Lianza at X-Rite. Our thanks as well to Danny Pascale (www.babelcolor.com) for allowing us to include his measurements of the spectral reflectance of a color chart. Thanks to Mikhail Polyanskiy for index of refraction data via refractiveindex.info and to Anders Langlands, Luca Fascione, and Weta Digital for camera sensor response data that is included in pbrt.

About The Cover

The Watercolor scene on the cover was created by Angelo Ferretti of Lucydreams (www.lucydreams.it). It requires a total of 2 GiB of on-disk storage for geometry and 836 MiB for texture maps. Come rendering, the scene description requires 15 GiB of memory to store over 33 million unique triangles, 412 texture maps, and associated data structures.