What is the difference between levels, curves and contrast settings in post processing?

Question

I have found and read a lot of tutorials that speak individually about curves, levels and contrast in post-processing but no luck so far about finding something that compares them.

It is my understanding that curves is the most flexible tool, while levels is more simplified and the contrast slider is even more simplified. Is this the case?

To put it another way. Am I correct to assume that I can do with curves anything that is possible with levels (and more)? Do I need to bother with the contrast slider at all if I am accustomed to working with curves?

Answer 1

Yes, your assumption is correct. A levels control is basically the equivalent of a curves control that can only be adjusted at the end points and one point in the middle, while a contrast slider is (usually) the equivalent of moving both ends at the same time (although some may be more sophisticated). The curves tool gives the most flexibility, but also allows you to create very unnatural-looking results.

Answer 2

I look at them kind of like sandpaper for a woodworking project: The Contrast slider is the really coarse paper that you use to get in the ballpark of the final shape you want, the Levels sliders are like a medium grit that allows you to fine tune the shape and get closer to your goal, and then the Curves allow the finest control like a really fine grain paper to smooth things out and give your projects its final shape. You could use only the fine grain sandpaper, but it would take forever to get from the starting point to the final shape.

Similarly, you could do everything you can do with Contrast and Levels using only the Curves controls. But in most cases it would take you a lot longer to get the image to appear the way you want it to.

Answer 3

This is really a basic "how do I do post processing" question, and it's beyond this group to do general tutorials of any length. I've linked to a couple of older questions with some links to some good resources and discussion on this topic.

That said, the general answer to your question is that you don't need any specific button or slider in Photoshop or Lightroom to process an image, because there are usually a dozen ways to get the look you want and you can get through to the look you want.

In older versions of Lightroom I was taught not to use the contrast slider and to use the tone curves. In current (LR 5) I've flipped around and I almost never use the tone curves any more in favor of other techniques, but I'm adjusting contrast on most images. It comes down to learning your tool, having a vision for the way you want an image to look, and putting enough practice into post processing to be able to manipulate the image to get to that look.

There is no "one way" to process an image, and there's no "one look" that's correct. What matters is your look. And more importantly, there's no magic formula to process images, there are lots and lots of them -- and you need to put enough time into learning enough post processing to understand which path you're comfortable with so you can produce good looking images in the way you like reliably and efficiently.