What is gamma, and how should colorists use it in their color grading practice?
Gamma is one of those things we all have an idea about. We see it at work, but it’s likely that only a few of us have a clear understanding of what drives the behavior of gamma and when we want to use it. So let’s dive into DaVinci Resolve and get a clearer look for what gamma is, how it works, and when we should and shouldn’t use it.
What is gamma?
The simplest answer is that gamma makes the image brighter or darker. But gamma is a powerful tool, and it provides a huge function in the world of color grading. It’s worth having a more detailed understanding of how it actually behaves. To get that understanding, we’re going to use my favorite visual aid, the grayscale ramp.
As you can see, we have this beautiful line running all the way from zero to one. With this line in place, we can evaluate what exactly gamma does within the DaVinci Resolve Primaries. Take a look at what happens to the waveform when I spin the Gamma wheel around.
The line becomes either a rainbow or a hammock, depending on if we move the Gamma wheel to the left or to the right. But notice that neither the zero nor the one hundred values are changing. Absolute black and absolute white do not change when we move gamma. Gamma only moves everything in between.
Applications of gamma in color grading
This behavior has all kinds of useful, interesting applications in the world of color grading. One technical application is when we want to prioritize the transmission of a signal to a monitor. It turns out that gamma is a good way to fill in the low end of our available bit depth. That’s why we use things like Rec 709 Gamma 2.4, because that display space is set up to respond to an image that has been encoded to something like what we’re using today.
One of the first applications of gamma came way back in the good old days, long before we had color management and all the fun tools that we use today. In the past, the most common way to color grade—the way, in fact, that I learned how to color grade—was to do all grading in Rec 709 color space.
Back then, we didn’t have a lot of latitude in our original camera negative to move things up or down. We had to work with a finite color volume. Basically, we had to work within the box of our display. All we could do was carefully move things around and make sure that nothing was clipping out.
Early colorists had to make sure they weren’t introducing any problems while color grading. Gamma was a vital tool for them because it pins down zero and one hundred and only moves the values between.
Gamma as an exposure adjustment
Gamma is also the closest thing that we are going to get to a photometric exposure adjustment. Look at what happens as I open up or shut Gamma while working in a Rec 709 Gamma 2.4 display space.
We’re not exactly getting an exposure response, but we are getting something reasonable, especially if we pair Gamma with our other Primaries. With Lift and Gain, we can get some pretty nice looking results out of our image.
Gamma vs. Offset
Let’s compare Gamma to another often-used tool, the Offset wheel. Offset is one of the most useful operators that we can use inside of Resolve. But using Offset in a display space, like Rec 709, is often a compromising choice. Look at how quickly and easily my shadows clip out when I spin the Offset wheel to the left.
See how quickly the shadows clip out? And if I now spin Offset to the right, something similar happens, but to my highlights.
The highlights go straight through the ceiling! So, Offset has limited utility in a display space. Gamma, on the other hand, is really useful because it pins down those maximum values.
Controlling tonality and color balance
Even when we are color grading in a scene space with a color managed workflow, gamma can still be an interesting way of delicately controlling tonality. For example, if you want to add a slight bit of extra weight into your image, but you don’t want to move your true black shadows, gamma can be a great option. That’s the exact nature of the tool, right?
But I don’t recommend using Gamma as your go-to tool inside of a color managed workflow. However, you should absolutely use it as a way of making nuanced, localized adjustments when you feel like the Offset tool isn’t quite working. The knob I usually reach for after Offset is either Gain or Gamma, and that decision is contextual. It depends on what you’re trying to do.
Now, let’s look at how we can use gamma to balance colors.
We can make a color balance happen by moving Gamma to the southeast without moving our zero or one hundred values. That means our whites and blacks are going to stay where they are, but all the colors between zero and one hundred are going to be gently moved.
Use the slider to get a better look at our Gamma color balance.
The importance of gamma
Gamma was the go-to tool for the first generation of creative colorists. Those colorists had four total wheels to work with—Lift, Gamma, Gain, and Offset—but Gamma gave them what they needed to feel their way to good results.
Gamma is a magical operator. It’s simple. It’s clean. It does something that no other Primary operator can do. And more than anything, it can be a great gateway to a tactile, feel-based relationship with the adjustments that you are making to your image.
Gamma can also teach you how to make adjustments by playing your tools off of each other as opposed to reaching for a single knob and expecting to get ideal results. Using Gamma can help you feel your way through your color grade and show you how to create subtle overlaps between two or more adjustments.
Wrapping up
Gamma has an amazing legacy as both a creative and a technical tool. It’s is how we transport images out to our Gamma 2.4 display, and it’s how those images end up getting decoded and shown to us. If you can better understand what gamma is doing under the hood, you can be more empowered and make better choices when it comes to using Lift, Gamma, and Gain.
Our goal as colorists is to understand the tools in front of us and to make amazing use of them. That’s what allowed that first generation of colorists, with their finite set of tools, to craft compelling, artful, and cinematic images. They knew how to use the tools they had and they understood what each of those tools did.
