How to choose between Gamma 2.2 and Gamma 2.4 when color correcting?

Gamma 2.2 vs Gamma 2.4 – How, Why and When (in DaVinci Resolve)?

August 23, 2017
Patrick Inhofer C.S.I.

When you start delving into the finer points of color correction you'll eventually learn about Gamma 2.2 vs Gamma 2.4. Learn how to choose between them.


How do you set up DaVinci Resolve for different Gamma settings (and why)?

We recently had a question come in about a common source of confusion:

What color & gamma settings should I use in FCPX & Resolve when it’s going either to the internet or onto DVD’s?

It’s a great question – but opens a can of worms when it relates to setting your gamma on your reference display and the various options in DaVinci Resolve. Why a can of worms? Because you have to consider not one but two different scenarios for setting your gamma:

  • Scenario 1: Your color correction / mastering environment matches the delivery / viewing environment. For example, your mastering environment is set for broadcast and you’re delivering for broadcast.
  • Scenario 2: Your color correction / mastering environment does NOT match the delivery / viewing environment. For example, you’re set for broadcast but delivery is for the Internet.

Each viewing environment has a different recommended gamma setting. And when it comes to setting gamma for color correction, what’s the rule for setting gamma?

1st Rule of Setting Gamma: It’s Based on Your Viewing Environment

Most discussions of setting gamma start with the display you’re using or your final delivery – but that misses the point of Rule #1: When mastering / color correcting your images, you set your gamma based on your viewing environment.

In fact, the differences in the standard gamma settings used by Mac and Windows versus the standard gamma settings for television or cinema are all based on overall brightness levels in the room!

Why?

It’s due to the Simultaneous Contrast Effect of human perception.

The Simultaneous Contrast Effect and How it Relates to Gamma Settings

Wikipedia has a good explanation of how Simultaneous Contrast works. But a single pictures really is worth a thousand words and in the image below, the gray square in the middle of both boxes have precisely the same brightness values (if you don’t believe me, just pull out a color sampler and check for yourself:

The Simultaneous Contrast Effect
The middle gray boxes have precisely the same RGB brightness values – yet they look different. Why? That’s the Simultaneous Contrast in action.

The reason the two middle boxes look like they have different brightness values comes down to human perception. The human brain make brightness assumptions comparatively, not absolutely. None of us has a built-in eyedropper tool that gives us absolute RGB readouts. Our perception of the brightness of an object in a room is effected by room itself.

And if those middle gray boxes are a television or computer screen, and the surround fields is the overall brightness of your room… what implication does that have while color correcting??

The exact same image, in two different rooms—one bright and one dark—will look different! Particularly the brightness values.

Using Gamma to Solve the Simultaneous Contrast Effect

How would you fix the problem of Simultaneous Contrast on the two boxes above? Let’s call the top box our ‘reference environment’; it’s the one with the dark surround field. To get the bottom box to match, we can apply a brightness adjustment to push the middle gray box brighter until its ‘perceived brightness’ matches our reference environment.

And that’s what precisely we’re doing when we move our images between Gamma 2.2, 2.4 and 2.6. We adjust those middle boxes to make them brighter or darker so their apparent brightness in the different viewing environments is equalized.

For most of us, the question comes down to choosing: Gamma 2.2 vs Gamma 2.4?

In this Insight, I’m not going to dive any deeper into the technical explanation of gamma (you can read that explanation on Charles Poynton’s site). But if you’re going to make an informed decision about choosing your gamma settings then you need to understand the standard gamma settings for different viewing environments:

  • Gamma 2.2 – This gamma setting is generally used for brighter viewing conditions. Think: Office setting with bright overheads and lots of indirect daytime light from exterior windows. Under these conditions, the viewing screen needs to pop the shadows or the image becomes a mushy mess and ‘lowering’ the gamma setting helps the image fight glare. Hence, gamma 2.2 is the standard gamma setting for Windows and has been the standard gamma setting on Apple computers since Mac OS 10.6 (prior versions of the Mac OS used gamma 1.8) since computer displays assume a bright, daytime viewing condition.

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