Here is a Photoshop technique for contrast that uses layers, one for the lights and one for the darks. Contrast can be adjusted with many commands in Photoshop: Brightness/Contrast, Levels, Curves, Exposure, to name a few. Layered contrast provides certain kinds of control you can’t achieve with the other commands. I’ll describe it step by step for you, by way of explanation, and also provide a downloadable action.
- Open an image to work with.
- Open the Channels palette (Window menu > Channels).
- Hold down the command key (control key on PC) and click the RGB channel: the light areas of the image are loaded as a selection.
- Open the Layers palette (Window menu > Layers) and press command-J to copy the selection to a new channel.
- Set the blend mode of the new channel to Overlay. The bright areas of the image get brighter.
- Command-click on the new layer to load it as a selection.
- Select the original layer.
- From the Select menu, choose Inverse. The formerly unselected areas of the image–the dark areas–are now selected.
- Press command-J to copy the selection to a new channel.
- Set the blend mode of the new channel to Multiply. The dark areas get darker.
And there you have the basics. To see the original channel by itself, option-click on it in the Layers palette (alt-click on PC).
You will probably want to adjust the fill or opacity of the two channels you created. Try 34% for the multiply and 47% for the overlay, for example–these are the values used in the Layered Contrast Action. You can also try using Soft Light blend mode for the light channel (not quite so bright) or Screen (brighter). In fact, now that you’ve got the light and dark areas into two different layers, you can experiment freely.