Understanding the Gamma value

In this movie I'll show you how to use the Gamma value to adjust the midtones…in an image independently of the Black and White points.…Now in my case, what I want to do is, I want to darken up the wall inside of this image.…It's looking awfully washed out, and the wall clearly falls inside the midtone range.…So what I need to do is drag this Gray slider around, and notice if I drag it…over to the right then I'm darkening out the image considerably.…You can also see what's happening to the composite histogram over here, all…the colors are moving radically over into the shadow arena, which is not what we want.…

If I drag the Gray triangle over to the left, you can see that I'm pitching the…histogram over to the right here into the highlight range.…Now this value here is a little bit confusing.…It's not a Luminance level like the Black and White points, instead it's an…exponent, and not to get too techy on you, but that means, that in this case,…we're raising the Luminance levels to a power of 2, that is we're squaring them,…