What Is Gamma?

What Is Gamma?

Gamma is one of those terms that gets thrown around a lot in VFX, and it causes a lot of confusion. Simply put, gamma is a mathematical curve applied to image data to adjust how brightness is distributed. It is not a color space, though it is often associated with one. Gamma encoding is used because human vision does not perceive brightness linearly, and neither do display devices. Without gamma correction, your images would look washed out or too dark.

Gamma values are expressed as a single number. A gamma of 1.0 means no correction, the image is linear. A gamma of 2.2 is standard for sRGB and most computer monitors. This curve takes the linear data from your render and redistributes it so that more precision goes to the darker areas, where the human eye is more sensitive. When the monitor displays it, it applies the inverse curve, and the image looks correct.

The problem is that many VFX operations need to happen in linear space, before gamma is applied. If you blur an image in gamma corrected space, you get dark halos around bright objects because the math is wrong. If you composite two elements that have different gamma assumptions, they will not match. This is why color managed pipelines are so important. They ensure that every operation happens in the correct color space.

Different devices use different gamma values. Macs traditionally used a gamma of 1.8, though modern Macs use 2.2 like everyone else. sRGB is approximately gamma 2.2 but uses a slightly different curve with a linear section near black. Rec.709 uses a gamma of about 2.4 for display. If you are viewing VFX work on an uncalibrated monitor, you cannot trust what you are seeing because the gamma could be wrong.

The practical takeaway is to always work in a color managed pipeline. Software like Nuke, Fusion, and After Effects have built in color management that handles gamma conversions for you. Make sure you tell the software what color space your input footage is in and what color space you want your output to be. If your renders look too dark or too light when you bring them into compositing, the first thing to check is your gamma settings.