From the Publisher
"How to" books are a dime a dozen. What makes this book special is that it is also a "Why" book. Hullfish sits down with world-class colorists and records not only what they do but why they do it. That's where the magic lies.
"How" is the question to ask if you want to become a craftsman. "Why" is the question that creates artists. I bought the first edition for "How" and came away with a lot of "Why." This edition has lots more of both, with material from several additional world class colorists.
If you want an inside look into the art and craft of the professional colorist there's no better way to do it in book form. Whether you're learning to be a colorist or just want to understand what really happens when you decide something can be "fixed in post," you need to read this book.
-Art Adams, cinematographer/educator, ProVideoCoalition.com.
This book just keeps getting better with each new edition. Steve Hullfish's approach is designed to teach techniques that transfer to a wide range of popular and accessible color correction tools. The intent is to demystify the process, so readers can learn the concepts and apply them, regardless of whether the software has sliders, wheels or curves. Best of all, Hullfish features extensive tips and tricks from some of the premier colorists in the country, so you can learn from the masters. If you only purchase one book on color correction, this is the essential guide to include in your library. - Oliver Peters, Oliver Peters Peters Post Production Services, LLC
A terrific and much-needed book for anybody serious about digital color correction. Starting with the basics, it helps the reader work through a series of specific, well-illustrated examples, covering all the major software applications, and supports the text with insightful comments from prominent working colorists. All in all, it's essential reading for anyone who wants to improve their skills in this rapidly changing field.
- Steve Cohen, editor, Emmy and ACE Eddie winner, author of "Avid Agility."
Read an Excerpt
The Art and Technique of Digital Color Correction
By Steve Hullfish
Copyright © 2012 Elsevier Inc.
All right reserved.
Chapter One Primary Color Correction: Tonal Range Primer
Color correction is generally broken down into two distinct processes: primary and secondary color correction. These two processes will probably always be referred to as two distinct processes, but the technology itself is starting to change the perception of how and why these two processes are used and when the colorist moves from one process to another.
Primary color correction is the process of setting the overall tone, contrast, and color balance of the image. Secondary color correction is an additional step that refines the image in specific geographical regions of the image or in specific color vectors of the image. Don't let that word "vector" scare you. There are a number of definitions of the word "vector" that are used when discussing color space. It basically means the specific location or coordinates of a color. A vector can also mean the direction that something is heading, from one point in space towards another. So, essentially, in the color correction world, "vector" is just the technical word that defines a specific "color." Think of a vectorscope, which is a tool that allows you to kind of see the "color wheel" (Figure 1.1). The vectorscope shows you where parts of the picture are on the color wheel. So the vectorscope shows you the vector—or location on the color wheel—for the elements of your video image.
The first step in any color correction is to assess the tonal range of the picture. What are the problems with the tonal range and how can you address them? From a purely technical standpoint, it seems like an easy question to answer. As a matter of fact, many color correction plug-ins or color correction systems built into nonlinear editors have "automatic" buttons that will attempt to spread out the tonal range for you based on purely technical information. These automatic systems assume that the brightest parts of the picture should be as bright as possible while remaining "legal." The darkest part of the picture is also set automatically to be as low as possible while remaining "legal."
There are two big problems with this behavior. Simply setting the brightest pixel to 100 and the darkest pixel to 0 with all of the intermediate pixels spread evenly between them does not necessarily provide the best spread of the tonal range across the most visually important parts of the image. The other problem is that the image may not need to have either its brightest pixel at 100 or its darkest pixel at 0.
The first problem is solved with some experience. Great colorists know tricks that can enhance the perception of an image's tonal range. They know that they can sacrifice the detail in a certain tonal range where it may not be noticed so that they can use that tonal range to enhance a more visually important part of the picture. These are tricks that you will learn in this chapter and throughout the rest of the book, Automatic software doesn't know what is visually important, so it treats all areas of the image equally.
Even if the image should be spread from 0 to 100, that still leaves out one critical component: gamma. Spreading out the tonal range really serves to increase contrast, but the real impression of how bright or dark the image is relies largely on your gamma or midtone controls. Gamma really refers to a curve. The reason that midtones are sometimes referred to as "gamma" is because by lifting or lowering the midtones, you are creating a curve between the white point and the black point instead of a simple straight line (Figure 1.2).
The second problem is that the image may not require an expanded tonal range (Figure 1.5). Most shots should have a pretty wide tonal latitude (range) with rich blacks and sparkling whites, but there are those images that should not take advantage of the full tonal range. Some examples: an igloo in a snow storm; a dark, moonlit close-up of a Navy SEAL creeping through the underbrush; a foggy, early morning rowboat ride; a long lens shot of a smoggy city at dusk. Each of these may only have a partial tonal range, lacking either a deep black or bright high- lights. However, these examples are usually the exceptions to the rules. But they do require the colorist to consider the clues in the image itself to determine whether anything in the image deserves to be completely black or bright white.
Keeping these exceptions in mind, let's consider the approach to most of the images that—as you will see—will benefit from spreading the tonal range as much as we can.
My first book on color correction, cowritten with Jaime Fowler—Color Correction for Digital Video—goes into detail about monitoring. I don't want to address those same issues as thoroughly in this book, but I will touch on them briefly.
Proper monitoring is crucial: you must have a well set up video monitor. There are instructions for doing this in my first book and on numerous websites and online instructions. Although LCD monitoring has been largely shunned by serious colorists, the production of CRT displays for video was halted several years ago, leaving many with no choice but to switch to LCDs or some other technology. The main issue with these LCD monitors is how colors and tones shift with the viewer's angle to the screen and how deep a black is able to be displayed. This problem is called off-angle viewing.
At a recent NAB (National Association of Broadcasters) convention, Sony revealed some beautiful OLED video monitors that largely resolved the off-angle viewing issue and improved performance in the blacks, which is a weakness of LCD video monitors. These monitors remain very expensive, but they're getting serious attention from the colorists and facilities that deliver high-end broadcast and film images.
Many LCD video monitors can be set-up with look-up tables (LUTs) or by using calibration hardware and software. The cost and accuracy of these calibration units varies widely from several thousand dollars to under a hundred dollars. For my computer, I use a midlevel unit by X-Rite called the i1Display Pro (about $240). It uses a hardware device and software to create a custom monitor profile that even takes ambient lighting into account. This device would not fulfill the expectations of a serious, full-time colorist, but it creates a profile that seems very accurate to me.
Many high-end video monitors also have hardware-based calibration options that can help properly calibrate them. As I mentioned earlier, for video monitors that aren't capable of being set up with a profile or LUT, my first color correction book offers an in-depth description of how to set up a monitor to color bars. There are also several resources for doing this available on the Web and from the monitor manufacturers. Ensemble Designs has an SDI to HDMI converter box that allows calibration of a consumer monitor. Instructions for calibration are included with the device.
At the higher end, the manufacturer Cine-tal has created a small box, called the Davio. A software application runs the Davio hardware and allows any monitor, even a consumer monitor, to be calibrated and matched to another monitor or to a specification. All of the calibration is done automatically and only takes a few minutes.
This type of device (or some kind of LUT box) is really necessary to get the most accurate color reproduction from your monitor. Simply adjusting the brightness, contrast, hue, and saturation on your monitor will not deliver dependable results. Instructions on using these devices for monitor calibration vary and are provided by the manufacturers. Entire seminar series are devoted to the topic of color management, so it's outside the scope of this book to provide it.
For serious color correction, consulting firms can be hired to set up your suite, making sure that the image is accurate at each stage of the postproduction process, creating a workflow that guarantees the integrity of the image throughout the process.
The viewing environment is also of critical importance. The lighting in a color-critical environment is daylight balanced, not tungsten. There is some debate over the exact temperature of "daylight," but it's about 6000–6500K. The daylight-balanced light is often used only as reflected light as opposed to direct light. For example, it is bounced off of a back wall behind the monitor. It is also fairly dim. The eCinema displays we used for most of the color correction sessions come with a separate, external, daylight-balanced backlight that actually matches the light used inside the monitor itself. It is designed to be placed behind the monitor, bouncing light onto the wall behind it. The light bouncing off the wall behind the monitor should be one-tenth the intensity the monitor when displaying 100 percent white.
Any additional lighting in the room can't increase this brightness level. The light sources should be 6500K bulbs or be filtered to reach that temperature. This color value is often referred to as D65. The "D" refers to daylight; "65" refers to 6,500 Kelvin. Actually D65's exact Kelvin rating is 6503.6. The actual color of daylight varies. D65 represents the color temperature at high noon in the northern sky.
No bulbs or light sources should be visible to the colorist's eyes while grading. Some color correction suites have a bulb near the colorist's desk that sends a beam of pure 6500K light to a small white card or tile near the colorist to act as a reference for pure white. This light can be turned on or off independently from the other lights in the room.
Walls should be a completely neutral gray: no tint at all. Paint mixers have a very hard time with this. Bring an 18 percent grey photo card to your local paint store and see if they can match it. Many color suites aren't painted at all but are instead covered in gray cloth, which cuts down on reflected light and glare.
Here's a simple test to prove how important the viewing environment is to good color correction. Look at the following squares and determine whether the blocks to the right are darker than the blocks to the left (Figure 1.6). If you're familiar with optical illusions, you can probably guess the right answer despite what your eyes are really telling you.
The color chips inside the black surround (to the right) appear to be brighter than the ones on the white surround (to the left). The black surround also makes the contrast ratio of the chips appear slightly lower. This is due to a thing called lateral-brightness adaptation, which means that a particular retinal receptor in the eye is affected by the brightness of the receptors coming in to its neighboring receptors, which helps us detect edges better. (For more on the color theory involved, check out Digital Color Management: Encoding Solutions by Edward Giorgianni and Thomas Madden [Wiley]. Publication Date: January 27, 2009 | ISBN-10: 047051244X | ISBN-13: 978-0470512449)
High-level colorists are very sensitive to their viewing environment. This sensitivity extends to very small stimuli, such as glowing on/off switches on equipment and the color of the trace of the waveform or vectorscope. Most colorists try to grade using waveform or vectorscopes that have a neutral trace and graticule color instead of the traditional green.
This obsession with surrounding environment used to include the option to turn off the bright white Mac menu bar at the top of the monitor when using Color (then FinalTouch). Color and some other color correction software applications, such as Avid Symphony, go so far as to allow the user to customize the application's graphical user interface (GUI) colors to be darker and less saturated. A look at the GUI for DaVinci Resolve makes this clear (Figure 1.7).
Waveform and Vectorscope Displays
Most of the waveform and vectorscope displays that are built in to the software of desktop applications are barely sufficient for color correction purposes. These scopes have two things going for them: they're free and they're convenient. Other than that, there's not much to recommend them. There are a number of reasons that they do not stand up to a professional's needs.
Excerpted from The Art and Technique of Digital Color Correction by Steve Hullfish Copyright © 2012 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.
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