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* Gives useful, practical techniques for matte extraction, despill procedures, compositing and color correction
* Companion CD-ROM offers readers numerous problem-solving examples to work through for deeper understanding for applying the book's techniques
* Digital Compositing is loaded with tricks, techniques and alternative solutions to the common thorny problems faced by today's compositors
Digital Compositing for Film and Video is a hands-on, practical how-to guide addressing the problems and difficult choices faced by the professional compositor in real-life situations. Readers are offered in-depth practical methods for matte extraction, despill procedures, compositing operations, and color correction - the "meat and potatoes" of all digital effects.
Written by a senior compositor with over ten years' experience in both feature film and broadcast television, this book offers a broad range of alternative solutions that will save hours of fiddling with composites trying to get them to look right when the basic tools aren't working. A companion CD-ROM provides examples of the many topics covered in this book.
Author Biography: Steve Wright has 15 years experience in CGI and digital effects for broadcast television commercials, feature films, ride films, and IMAX films. He has spent eight years as in-house executive producer and digital effects supervisor for CGI Studios. Currently, Wright is Senior Compositor & 2D Technical Director with Cinesite., Cinesite (Kodak subsidiary)CGI StudiosIMAX
Audience: Compositors, graphic artists interested in moving into compositing and digital effects, and postproduction professionals, as well as students in advanced postproduction courses and graphics courses.
The ultimate artistic objective of a digital composite 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 same lighting conditions, with the same camera. To do all of this well, it is important to have a substantial understanding of the technology, because many of the obstacles that you will encounter are, in fact, not artistic obstacles. They stem from underlying technical issues that are not at all obvious to the casual observer but create problems in the shot.
The designers of digital 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 and a library of techniques and different approaches to the problem.
It takes three distinct bodies of knowledge to be a good digital effects artist: the art, the 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 photo-realism. The knowledge of your tools is simply knowing how to operate your particular compositing software package. The third body of knowledge, which is technique, comes with experience. Eventually, you become a seasoned veteran, to the point where you are seeing most problems for the second or third time and you know exactly what to do about them. The beginner, however, is continually confronting problems for the first time and it takes time to run through all the bad solutions to get to the good ones. This book contains years of production experience.
Although 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's going on behind the screen. What I did in this book was first of all 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 who are, ultimately, visual thinkers. I hope that as a result you will find the light smattering of math relatively painless.
1.1 WHAT'S NEW IN THE THIRD EDITION
The advancement of time and technology have not rendered any part of this book obsolete, simply because it is about good technique – and good technique never goes out of date. However, the last couple years have seen an expansion of digital compositing into three new areas that now warrant that some new material be added to keep it current. For stereo compositing, a new section has been added. For the new techniques in compositing CGI, an entirely new chapter has been added.
1.1.1 Stereo Compositing
Hollywood has flirted with 3D movies (technically, they are stereoscopic, not 3D) on and off for the last 50 years. Now they are here to stay. The reason I make this bold assertion is because digital technology has, for the first time, made it technically and artistically practical. It will not go away this time. Further, the television manufacturing industry is tooling itself up to support 3D TV in the home.
All of this 3D production means, of course, 3D postproduction, which in turn means stereoscopic visual effects and compositing. Most major compositing programs now support stereo workflow, so to stay current with the potential job market you will want to become familiar with the concepts, terms, and processes that go into stereo compositing. To this end, a stereo compositing section has been added to Chapter 5, "Compositing."
1.1.2 Multi-pass CGI Compositing
When digital compositing first started out, it was all about bluescreen and greenscreen compositing. These are still very important today, and will remain so in the foreseeable future. However, CGI has rapidly improved in photo-realism and now makes up the bulk of the compositing done for visual effects. Indeed, some feature films are all CGI.
The trend line in CGI visual effects is to render the elements into more and more multiple passes that are then pulled together in the 2D department and given their final look. Multi-pass compositing like this has huge productivity and artistic control advantages that are only going to increase its use in the future. The upside for us, the compositors, is that we are now the shot finishers and our importance to the overall production of visual effects has increased dramatically.
1.1.3 3D Compositing
The tight coupling between the 2D and 3D departments has introduced a whole new thing – 3D compositing. The concept is that limited 3D capabilities are now built into most major compositing programs so that many of the tasks previously done in the 3D department can now be done in the 2D department, where they are faster and cheaper. This has again increased productivity for the overall visual effects production pipeline and made the compositor yet again more important to it.
The trouble with 3D compositing for a straight up 2D compositor is that it introduces an alien vocabulary with major new concepts to master. To that end, there is an entire section devoted just to introducing key 3D terms and concepts such as shaders, surface normals, UV projection, geometric deformations, and much more. There is also a major section describing the most important 3D compositing techniques, such as set extension, matchmove, camera projection, and others. Learning about 3D compositing is a must do for any compositor that wants to future-proof his or her career.
1.2 SPECIAL FEATURES
There are four special features designed to assist the reader to get more out of this book, each identified by its own icon. They provide tips for Adobe Photoshop users (we are all Adobe Photoshop users), mark production tips, alert you to videos on the accompanying DVD, and identify the Production Exercise that goes with that section of the text.
1.2.1 Adobe Photoshop
Adobe Photoshop Users — this icon is for you. It marks tips on how to achieve the objectives in the text using Adobe Photoshop. Although this is a book on digital compositing, the vast majority of the topics are also quite valuable to a Photoshop artist, even though they might be implemented somewhat differently or given a different name. Those differences are documented wherever you see the Photoshop icon. There are even three Production Exercises specifically designed to be done in Photoshop.
1.2.2 Production Tips
There are production tips scattered throughout the book and designed to show good technique for various types of real world production problems. The "Tip!" icon at left marks the text both to alert the reader that this is a production tip and to make it easy to find later when the need arises. There are almost 200 production tips marked in this book.
1.2.3 DVD Videos
This icon indicates that there is a QuickTime movie on the DVD to watch that supports the adjoining text. You will find these icons in Chapter 6, "CGI Compositing," as many of the concepts in that chapter are simply better visualized with a moving clip rather than static images.
1.2.4 DVD Production Exercises
This icon indicates that there is a Production Exercise on the accompanying DVD for the material that you just finished reading. It is complete with test pictures and step-by-step procedures for trying out the techniques described in the text. This will give you real world production experience creating effects and solving production problems that reading a book alone cannot do. Plus, it's more fun.
The Production Exercises are organized into folders, one folder for each chapter of the book. Inside the chapter folders are the Production Exercises, each on its own HTML page. Just load the HTML document with your favorite browser and it will tell you where the images are for that exercise and guide you through a challenging production exercise. The caption under the icon tells you the name of that particular exercise on the DVD. The sample caption here, "Ex. 1-1" means "Production Exercise Chapter 1, number 1." Take a minute now to go to the Chapter 1 folder on the DVD and load the HTML document named "Exercise 1-1." There you will learn more about how the Production Exercises work.
The images provided on the DVD for the Production Exercises are typically 1k resolution feature film proxies (1024 778), which is half the resolution of 2k feature film scans (2048 1556). Half-resolution proxies are normally used in feature film compositing to set up a shot and full-resolution 2k film scans would have been an undue burden on the DVD and your workstation, for very little added benefit. The 1k film scans were selected as a good compromise to be useful to both feature film and video compositors. The half-resolution proxy is large enough for film work but not too large for the folks working in video. When the topic is video, of course, video-sized frames are provided, complete with interlacing when appropriate. There are even full-resolution high-definition video frames to work with.
Most of the images are in the TIFF file format, as that is the most ubiquitous file format and is supported by virtually every digital imaging program in the known universe. For the exercises that specifically require log images, DPX files are provided, as DPX is becoming more prevalent than the Cineon file format for log film scans. They contain the same log data as a Cineon file, so the file format does not effect the results, but more readers will be able to read a DPX file than a Cineon file.
1.3 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 in 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 situation, the robust index will come to the rescue.
Part I: Making the Good Composite
The first part of this book is organized in the workflow order of the process of pulling a matte, performing the despill, and compositing the layers.
Chapter 2: How to pull mattes. There are lots of different kinds of matte for lots of different situations. There is extensive coverage of the all-important color difference matte that is fundamental to bluescreen compositing.
Chapter 3: Methods of refining mattes. Regardless of how a matte is extracted, it will usually need some "sweetening" to soften the edges, expand or erode the perimeter, or refine the slope of the matte edges.
Chapter 4: The all-important despill operation. How they work and the various artifacts they can introduce. Several approaches for creating your own custom despill operations are given to help solve troublesome discoloration artifacts.
Chapter 5: How the compositing operation works. What goes on inside of the composite node and how to deal with premultiplied and unpremultiplied images. Stereo compositing with a general background in how stereo works is included.
Chapter 6: How to composite CGI. First, the issues involved in working with premultiplied and unpremultiplied CGI are described in detail. Then there is a detailed exposé on multi-pass CGI compositing followed by thorough coverage of 3D compositing.
Chapter 7: Image blending operations. There are a myriad of ways to blend two images together other than the composite. Without using a matte, two images can be blended with a variety of mathematical operations, each with its own unique visual result.
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 light space, matching the camera attributes, and then matching the action.
Chapter 8: Matching the light space between the composite layers. Some background on the nature of color and the behavior of light is offered, then it's on to the subject of getting the different layers to appear to have been photographed with the same lighting. A checklist of things to look for in the finished composite is included.
Chapter 9: Matching the camera attributes between the composite layers. The camera, lens, and film stock affect the appearance of the layers and must be made to match for the different layers to appear to have been photographed by the same camera.
Chapter 10: Matching the action between the composite layers. An extensive look at motion tracking plus the effects of geometric transforms and their filters on images are explored. Techniques to make more realistic motion blurs and quick image lineup procedures are offered.
Part III: Things You Should Know
At this juncture, we have completed the basic composite, so the topics turn to a broad range of issues beyond compositing that affect the results of the job overall.
Chapter 11: The wacky world of gamma. Not just the gamma command for altering the brightness of images, but also how gamma works on images and in your monitor and with film, plus its effects on the display of images.
Chapter 12: Coping with video. The complexity of video images and why they are the way they are. Procedures for removing the 3:2 pull-down, de-interlacing, and how to deal with the nonsquare pixels are addressed, plus how to incorporate video into a film job. Both standard definition and high definition are covered.
Chapter 13: Film and film formats. Definitions for the different film apertures, what they are for, and how to mix images between them. How to work with CinemaScope and IMAX images, the workings of film scanners and film recorders, and an overview of the Digital Intermediate process.
Chapter 14: Log vs. linear film data. How film captures images, and what the heck log film data is anyway. Why log is the best digital representation for film and what happens to your pictures when you go linear anyway.
Chapter 15: Working with log images. How to convert log images to linear and back to minimize the picture losses with Cineon film scans. For the brave souls that work with log images and those that want to try, the procedures for doing digital effects in log space are explained.
1.4 TOOL CONVENTIONS
The slice tool, flowgraphs, and color curves are used extensively throughout this book to analyze images, show procedures, and modify pixel values. They are essential to the telling of the story, so this section describes each of them in order to develop a common vocabulary and overcome any terminology differences with your software. Your software may not have a slice tool, so it will be a new concept to some, but I'm sure you will quickly appreciate why it is such an important tool for revealing what's happening inside an image. Who knows — you may want your engineering department to whip one up for you after you see what it can do. Although the flowgraph is becoming the standard interface for compositing software, terminology differences and its absence in a few compositing packages warrant a quick review of how it is used in this book. Though all software packages have color curves, we will be putting this tool to some new and interesting uses.
1.4.1 The Slice Tool
The slice tool is a very important image analysis tool used extensively throughout this book to illustrate pixel events. Not many software packages have such a cool tool, so an introduction to its operation and why it is so helpful is in order. Use of the slice tool starts with drawing a single straight line across the region of interest of a picture, shown in Figure 1-1 as a diagonal white line. The second step is to plot the pixel values under the slice line on a graph, shown in Figure 1-2. We are starting with a grayscale image because it is easier to follow, then we will see it in action on a three-channel RGB image.
Excerpted from Digital Compositing for Film and Video by Steve Wright Copyright © 2010 by ELSEVIER INC. . Excerpted by permission of Focal Press. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
|Ch. 2||Pulling mattes||13|
|Ch. 3||Refining mattes||69|
|Ch. 5||The composite||101|
|Ch. 6||Blend operations||133|
|Ch. 13||Log vs. linear||353|
|Ch. 14||Log images||385|