The Curves Eyedropper technique provides a fast way to simultaneously correct color and fix exposure problems in your photo all at once. That’s a lot of benefit for just a few clicks.
Here’s how it works.
1. Open a photo that you think needs correcting.
2. Create a Curves Adjustment Layer by clicking on the Adjustment Layer icon in the Layers Palette, and then choosing Curves from the drop-down menu.
3. Near the bottom of the Curves Dialog, you will see a row of three eyedroppers. From left to right they are used to set the Black Point, the Gray Point, and the White Point.
4. Ideally you should set specific color values for each of these droppers (although you can skip this step and try it with the default values if you like). Double-click on the Black dropper to open its settings, and in the R,G,B values enter 20, 20, 20. For the Gray dropper: 128, 128, 128. For the white dropper: 240, 240, 240. Now we will simply click once in the image with each of the three droppers to correct color and contrast all at once!
5. Click on the black dropper to select it. Your cursor now looks like the dropper. Click the dropper once in the darkest part of your image. You are telling Photoshop “This spot should be black.”
6. Now click on the White Point dropper to select it. Click with the White dropper in the lightest part of your image. You are telling Photoshop, “This spot should be white.”
7. Now comes the tricky part. You need to use the Gray dropper to select a spot in your image that should be Neutral Gray. This does NOT mean a gray that is exactly halfway between white and black. That doesn’t matter. What matters is that the gray be neutral in color (i.e., its RGB values should be equal). It could be a very dark gray, or a very light gray, so long as it is neutral. Perhaps it does not not look neutral in your photo due to a color cast, but you know it should be neutral in reality. This can be challenging, unless you have an object in your photo that you know should be gray. But you can also don’t choose any gray if you don’t like to.
Compare the before and after photos, and it’s remarkable what Photoshop can do with three little clicks!