An Introduction to Color Grading

3Share

If you are a video editor or are looking to get into video editing, I have both good news and bad news. I’ll start with the good news. Never before have video editors had such an extensive set of color-correction and color-grading tools available at their fingertips. Over the last decade, the makers of non-linear editing software have strengthened the color-grading abilities of their software to the point where they now rival dedicated color-grading software in control and ability. Perhaps as a response to this competition, the developers of dedicated color-grading and VFX software like Davinci Resolve, Nuke, and Scratch have introduced non-linear editing tools into their software.

This convergence of NLE and color-grading software means that regardless of the program you choose to edit your video, this an exciting time to work in post production. With the powerful and precise control these tools offer, you can make day look like night, turn a warm sunset into cool dusk, or turn a red car blue. Video editors can change the entire mood of a scene or just the color of a single object in the frame without even rendering their timeline.

Don’t forget, I promised bad news, too. Here it is. This convergence of software has led to a blurring of the line between the roles of video editors and colorists. With access to these powerful color-grading tools, video editors are often expected to know how to use them.

It’s not uncommon for video editors to be called upon to balance the color of a scene, if not completely grade the video, as well. Fortunately, if you know what you are doing, color-grading is usually a fun and expressive process.

A Few Quick Terms

If you are already familiar with the vocabulary of video color, you might want to skip to the next section. If you are new to color correction, then before diving into the tools for the first time it’s a good idea to be familiar with the vocabulary of video color. Fortunately, this language is fairly consistent across most programs.

Hue refers to the “pure color” of a color without referring to how vivid, bright, or dark it is. When most people speak of a color like red or green, they are speaking about its hue.

A hue scale isolated from saturation or brightness
 

Saturation, in a basic sense, refers to how colorful a color is. Saturation varies between there being no color in an image and a pure color. A color image can be converted to a black-and-white image by reducing its saturation to 0.

A value scale, which controls brightness
 

Value / Lightness / Brightness / Luma  The terms value, luminance, lightness, and brightness all deal with how bright or dark a color is. However, they each refer to a different scale and have different relationships with saturation and contrast. The distinction between these terms can be important. Fortunately, interface designers who work in professional video software usually provide useful visual feedback to let you know if the brightness-adjustment tool you are using will influence your saturation.

Common Color Correction Tools

Color-grading might be an art, but it is an art that relies heavily on science and computer programming. To some, the user interface of color-grading tools might look like radar screens or Cartesian graphs from math class, but once you know what they do and how they work you will find that they have been expertly designed to help you work quickly and efficiently. It is also fortunate that the interfaces of most color-grading tools have been more or less standardized across different software. For example, once you learn to manipulate the curves tool in Davinci, you will know how to do this in any piece of video software.

White Balance

What does it do?

The white balance tools found in post production are based on the white balance setting found on professional video cameras. These tools offer you the ability to shift the color cast of your image to become either warmer or cooler on the Kelvin scale. The main purpose of this tool is to correct video that was shot with improperly tuned white balance settings; however, if the white balance tool in your software offers manual adjustment, it can be used creatively to simulate the look of specific natural lighting conditions.

White balance and tint controls
 

How does it work?

This may seem counterintuitive at first because the higher the setting is in degrees Kelvin (hotter), the cooler the colors in your video will become (bluer) and vice versa. A warmer color setting (fewer Kelvin degrees) can emulate sunset, whereas a cooler (higher Kelvin degrees) can make video look like it was shot under the bluish light of dawn or on an overcast day.

Some implementations of this tool only offer the ability to make automatic corrections using an eyedropper tool. This is helpful to remove an unwanted color cast created by improper white balance settings or unpredictable fluorescent lighting. Even when you encounter an automatic white balance, you can still achieve some expressive control by using a clever hack. Used normally, the eyedropper is meant to be used to identify areas of an image that should have a neutral color cast, but do not. However, if you click on a saturated color, the automatic white balance will tint your image with the complementary color to the one you chose.

Brightness and Contrast

What does it do?

In virtually every instance, this tool delivers exactly what is advertised: a set of two sliders where one controls the brightness of a scene and the other controls contrast. This may sound simple enough, but if you are unfamiliar with this tool, there are a few things you should know to get more out of it. It is important to remember that brightness and exposure controls are different. If you are looking to correct over- or under-exposed video, then you should turn to your software’s exposure adjustment tool first.

How does it work?

Another important fact to remember about this tool is that changing brightness can increase or decrease contrast. Conversely, changing contrast can increase or decrease brightness. These tools are most often bundled together for that reason. This complex relationship can make it difficult to achieve a specific fine-tuned look, unless you are well practiced in using these sliders together. This tool works best to quickly give your footage a small adjustment quickly, but for anything more nuanced, you might be better off using a curves tool, or a three-way color corrector.

Sharpening / Unsharp Mask

What does it do?

Sharpening tools are effective at increasing the perception of sharpness, but they will not help fix an out-of-focus image. Believe it or not, sharpening is not a tool that literally sharpens your image, but it is a trick that relies on a color correction of sorts. It was first developed for use in photo darkrooms. Sharpening and unsharp masks trick the eye to make an image appear as though it is sharper by increasing the contrast of certain edge pixels. Of the two tools, unsharp masks offer greater control, and allow you to create a more nuanced sharpening effect that doesn’t leave you choosing between sharpening all edges or none. Be careful to use these tools in moderation. When taken to the extreme, they can introduce a harsh look to your video. A helpful way to use these tools it to move all the sliders to maximum and then back them off until you are happy with the adjustment.

No sharpening Some sharpening Extreme sharpening

How does it work?

Unsharp masks work by creating a copy of your footage, blurring the copy and then subtracting the brightness of the copy from your original footage. All this blurring and math is invisible to you as the editor, but there are still a few controls to master. The overall amount controls the overall contrast between an edge and the adjacent pixels. Radius increases or decreases the blur, which widens or narrows the transition of contrast. Some implementations of unsharp offer a threshold control, which allows the user to define at which point contrast increases are applied.

Three-Way Color Corrector

What does it do?

The three-way color corrector is the workhorse of the color-correction industry. These tools offer the ability to control hue, saturation, brightness, and contrast all within a single interface. You may have seen colorists’ control surfaces like the Tangent Wave, or the Avid Artist Color. These devices were designed primarily to control three-way color correctors.

While three-way color correctors are not quite as precise as a curves tool, they are much faster to operate and far more user-friendly. Because they make it possible to get great results quickly, they are great for experimenting with different looks for your scene.

How does it work?

Three-way color correctors can seem intimidating if you’ve never used one before, but they are very easy to pick up. Each circular control has a point within it that the user can control by dragging it within the circle. Usually this point defaults to lying in the center. By dragging this point around the circle, you control the hue, while pulling this point closer to the edge or center increases or decreases saturation, respectively. Nearby each wheel is a scale or dial that controls brightness. Each of the three wheels will control either the highlights, midtones, or shadows of your video. These color wheels may also be labeled as gain, gamma, and lift. Three-way color correctors differ somewhat from software to software, but I’ve never encountered one that couldn’t get the job done. Interesting looks can be achieved by applying complementary colors to the highlights and shadows.


Before three-way color corrector

After three-way color corrector

This grade took less than thirty seconds to accomplish, using the settings below.

GUI of the Davinci Resolve color corrector


Fast Color Corrector

What does it do?

Fast Color Correctors are like the younger sibling to the Three-Way Color Corrector. With fewer controls to adjust and simpler color math than their older siblings, they offer speed in both adjustment and rendering time. This tool is perfect to set an overall tint or saturation adjustment to a video. While it is easy to use and experiment with, the number of possible looks you can achieve with it are limited.

How does it work?

Much like the three-way color corrector, hue is adjusted by moving around the center point while saturation is adjusted by moving closer or away from the center. There is often a brightness slider that accompanies the main circle.

Curves

What does it do?

Curves are perhaps the most precise and complex tools available in most color correction tool sets, and this makes them very powerful. They appear simple, but they can achieve the most complex and nuanced looks possible without secondary corrections. Curves remap the brightness of the overall image, as well as each individual red, blue, and green color channel.

Basic curves adjustment. The bottom axis is the original pixel value.
The horizontal axis is the pixel value you want.

 

How does it work?

Curves derive much of their flexibility from the graphic user interface. Curves are literally set up like a Cartesian graph with a curve running perfectly diagonally (x=y for the nerds) through it. The Y, or vertical axis, represents the light-to-dark pixels of the image before curves were applied, while the X, or horizontal axis, represents the light-to-dark pixels that will result. To control this tool, you add and drag points to the curve, which changes their shape. By bending curves, you can very precisely remap the brightness and contrast of pixels in the image.

This sounds complex, but there are a few tips that will help you make effective adjustments with this tool. Adjusting a curve to make it more horizontal lowers the contrast, while adjusting a curve to make it more vertical will increase the contrast. The power of curves comes from the fact that you can simultaneously adjust any of these settings. You can lower the contrast of the highlights, while increasing the contrast in the shadows.

Moving a point directly up or down will increase the brightness or decrease the brightness, respectively. By manipulating the individual red, blue, and green channels, you can create complex and powerful color effects.

Match

What does it do?

Match color (or Color Match) tools analyze the colors of a reference image and automatically adjust the colors of a target image to match. This is often used to match clips from shot to shot, or match video shot by different cameras. This can be a huge time saver, when applying a specific look to similar shots in a scene once you’ve gotten your reference shot to look the way you want.

Match Color uses the colors of one clip and applies them to another.
This is before match was applied.
After match is applied, the shots will look more
consistent when edited together.

How does it work?

Match tools are one of the few color manipulation tools that don’t offer a complex or interesting-looking graphic user interface. They tend to be simple buttons, or menu options, but don’t let this simplicity fool you. This is one of the more modern and advanced tools in color correction tool sets.

The creative potential of this tool lies in selecting the image you plan to use as your source. Think of it as creativity through curation. You can use this class of tools to match your video to scenes from a movie, a photo or advertisements. You can even use a painting. The image search on your favorite search engine just became a powerful tool in your color-grading arsenal.

Secondary Color Manipulations

Making color adjustments to an isolated portion of your video image is commonly called a secondary correction or secondary grade. Most professional video software includes tools for making these adjustments, although some software buries them a little deeper than others.

Whereas primary color changes transform the color of all pixels across an image indiscriminately, secondary color manipulations only apply to an area or color the editor or colorist has selected. Speaking figuratively, primary color changes paint with a broader brush. Primary changes are useful when you need to correct a poorly white-balanced scene, change the tint of the scene to set a mood, match shots of the same scene from different cameras, or make other general changes.

Secondary color corrections offer precision, and this is where the inner control freak in you can come out and play. By selecting only the portion of an image that you want to adjust, you have total control over the color of an image. The two most common ways to isolate pixels are with qualifiers and masks.

This fish is blue before secondary color correction. Secondary color correction allows you to adjust specific
colors in a shot without adjusting others.

Qualifiers

Qualifiers allow you to make adjustments to a specific color or a range of colors that you want to change while the rest of the image remains unchanged. Conversely, qualifiers can define colors that you don’t want to change while you are adjusting the rest of the colors in an image. Qualifiers work in a similar fashion to a chroma keyer, used to remove green-screen backgrounds. However, instead of selecting a color to replace it with another image, you are selecting a color to replace it with an adjusted version of itself. Like a chroma keyer, qualifiers often have you begin by selecting the colors you want to change with an eyedropper tool.


GUI for Davinci Resolve Qualitfier Panel

You can then refine your selection further by selecting small portions of the color scales for hue, saturation or brightness. The advantage of using qualifiers to isolate a portion of your image is that even as an object moves around the frame, they will continue to adjust only color you selected, as long as its brightness doesn’t change too much.

Masks

Masks, also known as Power Windows in Davinci, are a straightforward approach to isolating colors. You may be familiar with masks from Photoshop or another image editor. Masks in video software are not really that different from their counterparts, except that to follow a shape that moves around a frame, they sometimes need to be animated. This animation can be handled by either manually setting keyframes on the mask, or by automatically tracking a pixel, and having the mask follow the animation of track.

A geometric mask allows you to apply color correction to
the fish without affecting the surrounding colors.

 

Ultimately, the best-quality secondary color grades generally come from using a mix of masks and qualifiers. Masks help prevent qualifiers from picking up colors similar to the ones you selected but don’t want to adjust. Qualifiers help masks work better because you don’t need the mask to follow the edges of your objects so tightly. Together they are better than either would be alone.

Color adjustments are confined to this poorly placed mask.


Practicing Moderation

On a final note, modern color correction tool sets give you unprecedented power to affect the look of your video. However, having the power to make extreme color changes to your video does not mean you should necessarily use it in every scene. It may seem obvious, but first and foremost, color grading should serve the material you are working with. With all that control at your fingertips, this is sometimes easier said than done. Some of the most effective grades are the ones that go unnoticed.

If you do find yourself pushing the sliders to 100%, or creating curves with sharp turns, you will quickly realize another important reason to practice moderation in your color correction. Color correction tool sets, when pushed to their limits, have an uncanny ability to show off the otherwise unseen flaws in your video. Color correction can fix many on-set mistakes, but if used to an extreme, it may also exaggerate video noise, compression, incorrect exposures, and harsh lighting. Be aware to look for these flaws when making significant adjustment to your hue, saturation, or exposure levels.

3 Comments

Thanks!An interesting piece on something I am starting to think about (non-"serious" video with m43 cameras).  The pricers of the software mentioned are breathtaking when this is not your profession.  Are there simpler/less expensive tools to do this?

Davinci Reslove 12 lite is free to download. No time limit, Limitations are negligable and you won't notice them.

You're in a bit of niche market but I applaud your ambition. I don't know what's what on the Windows side but Mac's iMovie has basic color tools packed into it, and you can address the common situations. With the free version of Davinci Resolve you'd be jumping in at the deep end but if you're willing to learn it you'd have a powerful set of tools available. Like the article says, my guess is any non-linear editor you tried would have at least some color tools included. Good luck.

Close

Close

Close