There's been a lot of tutorials on the curves. But why should you use the curves over contrast/white balance/split toning, etc? In this tutorial by Denny's Tips, you'll learn 4 scenarios when you should be using the curves.
Curves is one of the most powerful and useful tools you can learn. You'll find it in Photoshop, Lightroom, Premiere, Capture One, Snapseed and more. Here are the scenarios when you should use the curves over other settings.
1. Curves vs Contrast
The contrast adjustment is a simple slider that increases contrast. The curves tool lets you have more control over the contrast. For example, you can add contrast that is stronger in the shadows as shown in the image below.
Curves can also let you adjust the black and white point to create a faded film effect.
2. Curves vs Exposure
Exposure isn't something that a lot of people use the curves for. First, the exposure adjustment in Lightroom and Camera Raw works better for recovering details.
So then why use the curves?
Let's say you create a preset that uses the exposure setting. When other people use your preset, it'll overwrite their setting. Then they will have to readjust the exposure. Imagine using the preset on 100 photos - that's a lot of wasted time!
How do you brighten/darken without using the exposure setting? With the curves. Create a point in the middle then drag up to brighten or down to darken.
3. Curves vs White Balance
You can use White Balance to make your photos warmer/cooler. But just like with the exposure setting, white balance should only be used for retouching - not color grading. Instead of using the white balance to make your image warmer (as an effect, not to fix the white balance), go to the Blue channel. You can create a point in the middle and drag it up for a cooler image or down for a warmer image.
4. Curves vs Split Toning
Finally, how is curves better than split toning? Split toning is great when it works. Using the curves is harder but gives you more flexibility. For example, if you want more fuller colors, the curves can do that. You can learn more about how to create duotones with this tutorial.
Asides from those abstract effects, you can also create subtle effects but control where the split toning gets cut off. In the example below, we lifted the blues in a narrow range of the shadows.