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. And that ends up brightening the image considerably. I want to show you something that you need to keep an eye out for. I'm going to click inside of this value and I'm going to press Shift up arrow a few times.

And notice that just raises the value in decimal increments, however it has a big effect on the image. I'm going to go ahead and zoom in here on the shadow inside of this window. And notice how much noise we're bringing out in that shadow. And that's something you really need to keep an eye out for when you're brightening images inside of Photoshop. And those shadows certainly need brightening but I'll show you a better way to do it in the next movie. All right, I'm going to zoom back out here. What I want to do instead is lower the gamma value. So I'm going to start things off just resetting it to its default of one, which does nothing.

Because raising the luminescence levels to a power of one keeps them the same. And then I'll press shift down arrow in order to lower that value to 0.9. And I want you to see over here in the histogram panel. I'll go ahead and update the histogram. We have a very nicely balanced histogram in deed, which is generally what you're looking for when you're correcting a photographic image. And that friends is how you adjust the gamma value here inside Photoshop.