First off, Gamma is maths. Maths is not my strong point. I can do basic maths, but anything slightly advanced loses me so don’t expect me to explain gamma very well in my own words.
This is possibly the most simplified explanation of gamma you will ever receive: The term “gamma” or “gamma correction” refers to the brightness of an image.
Gamma correction is, in the simplest cases, defined by the following power-law expression:
I read through some forums discussing gamma and came across a comment from a Michael Nash that explained it rather well and quite simply. This particular discussion was on a site called Cinematography.com so was very helpful as gamma was discussed in relation to cinematography. Below is what Mr. Nash had to say about the topic.
In video cameras you can often adjust the master gamma, which makes the midtones brighter or darker relative to your exposure, and in turn makes the adjacent highlights and shadows appear higher or lower in contrast, depending on which direction you go. For example if you raise the gamma and make the midtones brighter, the highlights get “squeezed” or lowered in contrast while the shadows get stretched to a higher contrast (and some brightness). The opposite gamma adjustment has the opposite effect. […] This all becomes important to us cinematographers because we’re “painting with light,” and the gamma curve of the system we’re using is part of our palette. We want to know if the dark shadow we’re looking at on set is going to come out detailed brown, or completely black. By understanding gamma we can choose to exploit, or compensate for, the characteristics of the system we’re using to get what we want up on the screen.
And here is an image that hopefully makes me look like I understand what I’m talking about: