Tone Curves: Final Tips, Tricks, and Things to Avoid

We've had quite a journey with this whole histogram and curves ordeal:

• How to Read Image Histograms
• Photo Editing With Histograms: 6 Basic Settings
• How Well Do You Know Your Curves?
• Photoshop Curves Video Tutorials
• Linear Curve Adjustments and Histograms
• Nonlinear Curve Adjustments and Histograms

And now I'd like to wrap things up with a few tips, tricks, and things to avoid when using curves. It's a fairly simple tool once you begin to work with it and understand it, but there are a few non-obvious items worth pointing out.

TIPS

We'll start off with a few generic tips for working with curves, then we'll move on to the some of the more detailed stuff.

• Always work with 16-bit images to avoid posterization.
• In Photoshop, utilize layers and adjustment layers for non destructive editing.
• Use the color channel adjustments to correct color cast.
• Start subtle in ACR/Lightroom (or with an adjustment layer in Photoshop), then bump it up or add another layer if you need more.
• In Photoshop, use a levels adjustment first rather than a linear curves adjustment, then go to curves for a wider range to work with.

TRICKS

Here are a few tricks for the ACR/Lightroom interface under the “Point” curve.

• Hold Ctrl and mouse over the image to see where the tones lay on the curve/histogram.
• Ctrl+click over the image to set an adjustment point on the curve.
• Ctrl+select adjustment points on the curve to delete them.
• Ctrl+Tab to move between adjustment points without using the mouse.
• Shift+select multiple existing adjustment points if you want to grab more than one at a time.
• Shift+click over the image to set your neutral point for white balance (this works outside of the curves dialog too).
• Shift+arrow keys to move selected adjustment points by 10 rather than 1.

And then we have a few general tricks:

• Use extreme curves adjustments to separate tones for creating masks. Then remove or turn off the adjustment layer once you have the mask. (tip via Niels Henriksen)
• Use curves in LAB mode on the lightness channel to minimize saturation effects of adjustments.
• Boost your saturation using LAB mode curves adjustments on the A&B channels.

THINGS TO AVOID

• Watch for vertical sections in your curve — that produces an extremely high contrast and you lose all midtone data in that area.
• Watch for horizontal sections in your curve — that produces zero contrast and you lose all midtone data in that area.
• Too many adjustment points will be difficult to manage, just use what you need.
• Avoid inverted slopes, they invert the tones. Can you roll a ball from the upper right point of the curve to the lower left (without relying on momentum)? If not, you've inverted a section of your curve.
• Don't clip your shadows and highlights (unless that's what you really want to do). Keep an eye on your histogram for this one.

I'm sure there are a few hundred other tips and tricks out there for using curves, but I don't know them all and I couldn't cover them in one article even if I did. These tips, combined with the previous articles linked at the top, should keep most of you busy for a while. And if you're looking for more, here's my final tip on the subject:

Experiment. Try things out, push buttons, make mistakes, and keep learning.