Understanding the Gamma value

In this movie, I'll show you how to use the gamma value to…adjust the mid-tones 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 mid-tone 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 grey triangle over to the left, you can see…that I'm pitching the diagram over to the right here into the highlight range.…Now, this value here is a little bit confusing.…It's not illuminates level like the black and white points.…Instead it's an exponent. And not to get too techie…on you, but that means that in this case we're raising the…luminescence levels to the power of two, that is we're squaring them.…