Levels is one of the most useful Photoshop tools I know of. It can be used to correct both color and contrast. It takes a little practice and some trial and error, but it can work wonders to improve your photos. I'll show several examples over time of how this tool works in various situations.
Today’s tutorial starts with an overly dark photo. This can happen a lot when photographing paintings with a lot of white in them. Let's see if we can fix it. (Note that it’s already been cropped and aligned as per tip 2. I've made a duplicate layer to edit on.)
Click Ctrl + L (or Cmnd + L for Mac) to open the levels dialog box
(it can also be accessed from the top toolbar: Image/Adjustments/Levels)
(Note: I've shown a duplicate file to better show how the levels works)
Using the default tab (Channel: RGB), slowly adjust the three arrows until the image is closer to your original art. I suggest starting with the middle arrow first:
- the basic rule for the middle arrow is left is lighter, right is darker.
- To darken your darks, move the left point inward;
- to lighten your lights, move the right pointer back towards the center.
- Make sure the 'preview' box is checked so you can watch the transformation.
- If at any point you feel you've lost control, click cancel and start again.
- Once the image is where you want it, click Enter.
This image will still need a little color correction, but you can see how much improved the photo is with this one simple step.