The tone curve is not the most intuitive feature of Lightroom or Photoshop. In this tutorial I will explain how to read the curve, and then how to use the basic version of it in Lightroom and Camera Raw. Note that this is a rewrite of an old post. If you are a Photoshop user, you will want to read the old one (but keep in mind that the Lightroom information is out-of-date there.).
The tone curve is used to brighten or darken tones in your image. For general image brightening and darkening, I usually start with Exposure in the Basics panel to set how bright the brightest tones in the image should be, and then I move to the Brightness slider to set overall image brightness. Finally, I go to the Tone Curve when I want to affect just particular ranges of tones — for example, perhaps I want to brighten just the shadows or darken just the highlights in an image. In Lightroom, it is the panel directly below the Basics Panel in the Develop Module. In Camera Raw, it is the second symbol from the left below the histogram.
Reading the Tone Curve
Let me first say that if at the first mention of “graphs” and “X and Y axes”, your eyes are about to glaze over, you can skip down to “Using the Basic Curve”. You don’t have to know how to read the curve to use the basic version. However, consider giving it a try! If you fall asleep, I will take full responsibility — just please don’t read this while you are driving.