PSD Basics The Use of Histogram

This Photoshop tutorial will be explaining the very basics of the use of histogram.
When working with pictures in Photoshop the histogram is a very useful tool to get a better view of where you have your highlights, mid tones and shadows. Here's an example of a histogram.

To the most left you got your shadows, in the middle you got your mid tones and to the most right you got your highlights. When you work with your pictures you should always check your histogram. If the histogram has any clipped out highlights or burned out shadows it is probably because you are working with an under- or overexposed picture.

If you take a close look to the underexposed picture you will see that it has burned out shadows. You can see that because the graph tops on the most left. It's quite a small line but if you take a look at the overexposed picture it is even easier to see my point. The overexposed picture have a much wider clipped highlight. These pictures are barely any good working with because of the clipping.

Shadows & Highlights in Photoshop

So lets take picture with no burned out shadows or clipped out highlights and see if we can make it even better.

So here we got a picture with a "normal" histogram. We got no burned out shadow or any clipped highlights.
Lets try and improve this picture and apply a bit more contrast using the highlights and shadow option in Photoshop, Image > Adjustments > Shadows/Highlights. While still having your histogram open you can try apply a bit more contrast by dragging the amount of shadow and highlights.

To the left: After - To the right: Before.
As you can see that the after picture has a lot more mid tones now than it had before. When I work with pictures I usually try to get a nice balance of shadows, mid tones and highlights.

Working with Levels in Photoshop

There is also the Levels option in Photoshop when you want to apply more contrast to your picture, Image > Adjustments > Levels (Ctrl + L).

This looks very much like a normal Histogram but with a few tools. You can drag and drop your shadow, mid tones and highlights. When moving the left arrow you make your darkest pixels white and when doing it with the right one you make your brightest pixels black. This way you can easily control your highlights and shadows. There is also an auto option if you want to use that but I'd recommend you working a bit with this manually just to get the feeling of it.
If you hold down the Alt key while dragging you can see which pixels in your image that are affected by this move.

That was pretty much all I had for this Photoshop tutorial. Later in the chapter, "Adjustments layers", I will teach you how to work with these contrast tools in a non-destructive way. The method you just read about is a destructive way of working with Photoshop. Oh well, you can always just undo, but with the Adjustment layers you will always be able to see your original photo and you can easily change the parameters of your adjustments.