Levels or Curves?

What is the difference between Levels and Curves? Which of them should I use to edit my photographs?
Sumit Yadav, New Delhi

This story was originally published in October 2014.

Levels and Curves are extremely useful functions that help you do basic editing like altering exposure and contrast. However, there is a significant difference between both, that one needs to understand before manipulating an image.

Levels is the linear representation of all the tones in an image, while Curves is a graphical representation. The Levels dialogue box shows you the histogram of the image, but it only has three control points. On the other hand, the Curves dialogue box is a graph that allows you to click on any point and control the way the image looks. Now, which of these should you use while editing your photographs?

Technically speaking, since Levels has only three control points, it does not offer you the amount of control that the Curves function does. Yet, you can use both Levels and Curves to enhance your image. Use the Levels function to set the black point (darkest tone) and the white point (brightest tone) in your image. Set these points at the end points of your histogram to optimise the exposure and contrast of the overall image.

Now, since you have only one middle grey control point in Levels, you can do the rest of the editing in Curves. Curves allows you to edit a number of control points in the overall graph. This can be used to enhance certain parts of the image as well.

Expert users use both Levels and Curves minimally to avoid damaging the image information. Excessive use can lead to problems like posterisation.