Most image editors will work with Levels and Curves on an image to :-
Levels – Set the white and black point
Curves – Decrease the values of black and increase the value of white
Both of these in combination will help create contrast in the image, and ultimalty more interesting to look at.
These operations are typcially performed using an adjustment layer for Levels and independently a curves layer.
Actually Photoshop can perform both of these operations just on the curves adjustment.
Let’s take this image. It’s a bit flat, so by working on both Levels and Curves on a Curves layer, we can make it more interesting, just in a single step.
First thing is to create a new Curves layer, using the menu item, Layer, New Adjustment Layer and Curves.
When working with Levels, it’s beneficial to show the clipping points, this will make it really easy to see where the black / white points start to clip to black or white. The clipping indicators are available on the curves panel, by turning it on in the fly out menu. Once the curves dialog box is open, click on the fly out menu (marked in red), and select ‘Show Clipping for Black/White points’.
Now the clipping points have been turned on, when the left hand slider is moved towards the right (marked in red below), at some point the black points will show (as below) when they clip to pure black. The outcome of this, is that the details in the shadow will evetually be erroded away and detail will be lost (can be used creatively, but this type of precision will help control the black point).
The same can be applied to the highlights area, by moving the right slider to the left (be carefull with the white clipping point, as it will clip to white and can be offputting for the viewer when shown on a backlit screen).
Once the white and black points have been set, then the curve can be applied, in this case an ‘S’ curve.
That’s it. Photoshop levels and curves, just saved me an extra step. This can also help when used on a mask, or a clipping mask , as all operations are on a single layer, which in turn will make the document simpler with less layers to adjust and think about.