Understanding Gamma Settings

[ This article was first published in the August, 2009, issue of
Larry’s Final Cut Pro Newsletter. Click here to subscribe. ]

John Menszer sent me the following:

I and my friends have always had this problem- the video looks great in the Canvass but when it is exported to Quick Time it looks washed out. I recently stumbled across this Apple support article (support.apple.com/kb/HT2912), which discusses Gamma settings.

 

But I don’t know what they mean. Can you help?

Larry replies: Gamma controls where the mid-point of gray is set. On the Mac, traditionally, gamma is set to 1.8. In video, gamma is set to 2.2. The easiest way to see this is via an illustration.

The only difference between these two images is the gamma setting. The image on the left has a gamma of 2.2. Notice how the image seems darker than the image on the right with a gamma of 1.8? The blacks and whites of both are at exactly the same level. The only difference is where the grays are set.

(Thanks to my actress niece, Resmine Atis, for the use of her head-shot.)

In general, for all operating systems EXCEPT Snow Leopard, set your Mac Gamma to 1.8. This is where most Mac applications expect to find it. Final Cut, however, knowing that it is editing video, resets the computer monitor gamma to 2.2 while you are running Final Cut. This means that you see your video correctly within the program.

As Apple’s tech doc states:

“While it is possible to re-calibrate Apple displays via the Display Calibrator Assistant in Displays preferences, users should leave the gamma of their monitors to the 1.8 Standard Gamma setting when working in Final Cut Pro. ColorSync settings are not used by either Shake or Final Cut Pro for automatic color calibration or compensation of any kind.”

The trouble comes, as John discovered, when you view videos outside of Final Cut, because they appear lighter than you expected.

In the past, the principal distribution media for our projects was tape. When we laid video off to tape, this difference in gamma setting was handled automatically during the tape lay-back so that material in Final Cut and on tape looked correct.

So far, no problem.

However, now, tape is the exception, not the rule. Most of our projects are sent to the web. And, here, the differences in gamma between Macs, PCs, and video become most apparent.

(This is the reason in my tutorials on video compression, I show you were to set the gamma setting during compression so that you can adjust for these differences as you are compressing the file.)

With the release of Snow Leopard, Apple is changing its default gamma setting to 2.2; so this problem of matching gamma goes away.

However, until such time as he decides to upgrade, John asks another very relevant question:

“Usually I am making videos to deliver to others who will project it to an audience. I thought I was giving them the best quality by handing them a QT movie and getting them to play it full screen in Quick Time Player Pro. Instead of compressing it to DVD format and suffering the quality losses of compression. If there is going to be no DVD how should I set the gamma?”

Here the answer is a bit more complex. First, QuickTime does not allow you to adjust the gamma setting of a movie. Nor does Final Cut Pro, gamma adjustments are available for still images, but not video.

However, there are two relatively easy solutions, seeing as you want these to be projected as QuickTime movies.

If you are projecting the QuickTime videos using a properly calibrated PC, there’s no problem, as PCs and video share the same gamma.

If you are projecting the QuickTime movies from a Mac, changing the system gamma to 2.2 for the purposes of projection also solves this problem.

Fortunately, there’s a very easy way to do this. Go to Apple menu > System Preferences > Display and select the Color tab.

When you want to display video with the correct gamma, select SMPTE-C (PAL users can select PAL/SECAM). When you want to go back to your standard Mac gamma, select Apple RGB, or the setting that was selected when you entered this screen.

Simple – once you know why.

UPDATE – Aug. 30, 2009

Luca Immesi adds:

About installing Snow Leopard: Although, as you said, it’s always recommended to wait for a system upgrade, the change to gamma 2.2 in SL is a huge advantage to consider. It’s the first time I have a gamma consistency on my mac between applications without tweaking here and there.

Larry replies: Thanks, Luca! The gamma change is huge, but I’m already getting emails from pepole with problems. It won’t hurt to wait a bit longer.

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