2. Levels & Curves Eyedroppers

faq229-3720 introduced the basics of using Levels and Curves, so this FAQ will fill in the some of the gaps.

You may have noticed three eyedroppers in both the Levels and Curves dialog box. These are incredibly useful in both color & tone correction.

In simple terms, if you know a particular point in your image should be black, select the black eyedropper, and click that point. Do the same with the white eyedropper for a point you think should be white. There you have it, a full tonal range in your image!

In reality, you will probably get better results if you set a slightly off-white and off-black. That means that if there are lighter pixels in your image, they will remain slightly lighter, and some shadow detail is also retained. It also means that printed images don't have white 'holes' in them, a common enough problem.

So, double click the white eyedropper and give it a slightly off-white color (I usually use HSB, with settings of 0,0,96). Now click on your white point in the image. Do the same with the black eyedropper (only with darker values - say 0,0,4).

Notice these are neutral colors. This is important, and it's important that the highlights and shadows you pick in your image should be neutral too. When you click on these points, it will affect the color balance of the whole image. If there is a color cast over the whole image, but you know part of it should be black or white, then very often using these eyedroppers to tell Photoshop that they should be neutral will correct a lot of the color cast throughout the image. The gray eyedropper can also guide the colors in the image.

Although it takes a bit of practice to get it right, you can keep on clicking with any of the eyedroppers for as long as the dialog box is open.