Digital Compositing for Film and Video

Production Workflows and Techniques

Steve Wright

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781315283999
• Edition: 4
• Topic: Mezzi di comunicazione e arti performative
• Subtopic: Regia e produzione cinematografica

Written by senior compositor, technical director and master trainer Steve Wright, this book condenses years of production experience into an easy-to-read and highly-informative guide suitable for both working and aspiring visual effects artists.

This expanded and updated edition of Digital Compositing for Film and Video addresses the problems and difficult choices that professional compositors face on a daily basis with an elegant blend of theory, practical production techniques and workflows. It is written to be software-agnostic, so it is applicable to any brand of software. This edition features many step-by-step workflows, powerful new keying techniques and updates on the latest tech in the visual effects industry.

Workflow examples for:

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• Grain Management

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• Lens Distortion Management

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• Merging CGI Render Passes

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• Blending Multiple Keys

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• Photorealistic Color Correction

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• Rotoscoping

Production Techniques for:

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• Keying Difficult Greenscreens

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• Replicating Optical Lens Effects

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• Advanced Spill Suppression

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• Fixing Discoloured Edges

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• Adding Interactive Lighting

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• Managing Motion Blur

With brand new information on:

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• Working in linear

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• ACES Color Management

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• Light Field Cinematography

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• Planar Tracking

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• Creating Color Difference Keys

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• Premultiply vs. Unpremultiply

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• Deep Compositing

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• VR Stitching

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• 3D Compositing from 2D Images

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• How Color Correction ops Effect Images

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• Color Spaces

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• Retiming Clips

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• Working with Digital Cinema Images

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• OpenColorIO

A companion website offers images from the examples discussed in the book allowing readers to experiment with the material first-hand.

1
Getting Started

The Compositor’s Creed:

The ultimate artistic objective of compositing is to take images from a variety of different sources and combine them in such a way that they appear to have been shot at the same time under the under the same lighting conditions with the same camera.

Steve Wright, 2001

To do all of this well it is important to have an understanding of the technology of compositing because many of the obstacles that you will encounter are, in fact, technical problems. They stem from underlying technical issues that are not at all obvious to the casual observer but create problems in the shot. One example would be a double premultiply introducing dark edges around an element in the comp.

The designers of most visual effects compositing software have tried mightily to create a software tool that hides the technology so that it can be used by artists, and to a large degree they have succeeded. However, no amount of artistic training will help you to pull a good matte from a bad bluescreen or smooth motion track jitter caused by grain content. Problems of this sort require an understanding of the underlying principles of the digital operations being used to create the shot plus a library of techniques with multiple approaches to a problem. To that end, this 4th edition of this book contains a great many step-by-step workflow examples for keying and visual effects compositing.

It takes three distinct bodies of knowledge to be a good visual effects artist – art, tools, and technique. The artistic knowledge is what allows you to know what it should look like in the first place in order to achieve photorealism. The knowledge of your tools is simply knowing how to operate your particular compositing software package. The third body of knowledge, technique, comes with experience. Eventually you become a seasoned veteran where you are seeing problems for the second or third time and know exactly what to do about them. The beginner, however, is continually confronting new problems and it takes time to run through all the bad solutions to get to the good ones. This book contains over 20 years of production experience to help you get to the good ones faster.

While digital artists are invariably smart people, being artists they undoubtedly paid more attention in art class than in math class. But math is occasionally an indispensable part of understanding what is going on behind the screen. What I did in this book was, first, avoid the math wherever possible. Then, in those situations where the math is utterly unavoidable, it is presented as clearly as I know how, with lots of visuals to smooth the path for artists that are, ultimately, visual thinkers. I hope that as a result you will find the light smattering of math relatively painless.

1.1 How this Book is Organized

This book is organized in a task-oriented way rather than a technology-oriented way. With a technology-oriented approach all topics relating to the blur operation, for example, might be clustered into one chapter on convolution kernels. But blurs are used in a variety of work situations – refining mattes, motion blur, and defocus operations, to name a few. Each of these tasks requires a blur, but trying to put all of the blur information in one location is counter to a task-oriented approach when the task is refining a matte. Of course, scattering the blur information across several chapters introduces the problem of trying to find all of the information on blurs. For this issue a robust index comes to the rescue.

Part I – Making a Great Composite

The first part of this book is organized in the workflow order for the core tasks of pulling a key, performing the despill, and compositing the layers for both greenscreen and CGI shots.

Chapter 2: Pulling Keys – a million ways to pull a key. All about luma keys, chroma keys, difference mattes, bump mattes, color differences mattes plus an extensive section on professional rotoscoping techniques.

Chapter 3: Working with Keyers – pulling a key with a keyer. The internal workings of keyers, how to build your own After Effects keyer, coping with problem greenscreens and extensive techniques on preprocessing the greenscreen including the awesome screen-correction process.

Chapter 4: Refining Mattes – refining matte cores and edges. Using viewer “gamma slamming” to reveal matte defects, procedural techniques for creating garbage mattes, use of the media filter for noisy mattes, expanding, contracting and sculpting the matte edge falloff.

Chapter 5: Spill Suppression – multiple spill suppression techniques. Sources of spill and how despill works. Different spill suppression algorithms, my unspill operation, detecting and preventing despill artifacts, dialing in the edge color for the comp, and the edge-extension technique for fixing discolored edges.

Chapter 6: The Composite – a survey of methods for setting up a greenscreen composite. A look at the Over, AddMix and KeyMix composites, the Processed Foreground method, compositing inside the keyer, compositing outside the keyer, creating the Uberkey, and stereo compositing.

Chapter 7: Compositing CGI – proper technique for combining multi-pass CGI renders. Working with AOVs, ID passes, and normals relighting. All about EXR files, High Dynamic Range (HDR) images, and a large section about deep compositing.

Chapter 8: 3D Compositing – all about 3D compositing. Includes a short course in 3D explaining 3D terms and concepts for compositors. Camera tracking and how it is used, classic 3D compositing setups, an explanation of Alembic geometry and how to work with it.

Part II – The Quest for Realism

After we have a technically excellent composite we turn our attention to color correcting the layers to make them look like they are in the same lightspace, then adding several subtle effects such as light wrap that help to visually integrate the layers, and finally further blending the layers with camera effects such as vignetting.

Chapter 9: Color Correction – techniques for great color correction. First an understanding of light and light propagation, all about gamma, then a detailed explanation of the color operations (lift, gamma, gain, etc.) with their affects on appearance, on the code values, and when to use which one. Then a step-by-step process for color correcting a comp.

Chapter 10: Sweetening the Comp – a dozen things to do to make your comps more photorealistic. Adding interactive lighting, edge blending, light wrap, layer integration and creating realistic shado...