Getting more from Curves in Paint by Zaweba

If Levels gives you three handles on a picture's tones, Curves gives you as many as you like. It's the most flexible tonal tool in any photo editor, and once it makes sense it becomes the adjustment you reach for first. Paint by Zaweba's Curves adds a few helpers that make it easier to use well.

The basics

The curve runs from shadows at the bottom left to highlights at the top right. A straight diagonal line changes nothing. Push a point on it up and those tones get brighter; pull it down and they get darker. The tones around the point follow smoothly.

A histogram sits behind the curve, so you can see where the picture's tones actually are. There's no point bending the curve in a range with no pixels.

You can add any number of points. Most good edits use two to four.

The classic Curves move is the S curve. Pull a point in the shadows down a little and push a point in the highlights up a little. The middle stays put, the ends spread apart, and the picture gains contrast, more gently than a contrast slider.

The reverse, an inverted S, lowers contrast for a soft, faded feel.

Drag in image

Drag in image is the helper that makes Curves friendlier. Press on a tone in the preview and drag up or down. A point is added at that tone and moved. You don't need to work out where a dark jumper sits on the curve; press on the jumper and drag up to lighten it.

The Pencil lets you draw the curve freehand, and Smooth tidies a drawn curve into something gentler. These are for creative effects, like strange solarised tones or stepped contrast, rather than everyday correction.

As with Levels, a clipping warning shows where you've pushed tones to pure black or white. Steep curves at the ends can clip quickly, so it's worth turning on when you're adding strong contrast.

LCh and cross-channel curves

Paint by Zaweba also has perceptual LCh curves. LCh describes colour as lightness, chroma (how colourful) and hue, in a way that follows how we see. A lightness curve here changes brightness with less shift in colour than an RGB curve, which often makes saturated colours go strange when contrast is added. A chroma curve can boost dull colours without touching ones that are already strong.

Cross-channel curves go further, letting one property drive another. That's specialist work, but it opens up precise colour corrections.

Working well with Curves

Use it as an adjustment layer so you can change it and mask it later.

Make small moves. Curves is powerful, and a point moved a short distance often does the job.

Work in the RGB composite for contrast and brightness. Use the red, green and blue curves for colour, such as a slightly lifted blue in the shadows for a cool look.

Curves that misbehave

Too many points is the commonest problem. A wavy curve creates odd bands of tone. Remove points you don't need.

Ignoring colour shifts is another. Strong RGB curves can push saturation. If skin goes orange, try the LCh lightness curve instead.

And don't forget the histogram. If you're bending a part of the curve where the histogram is empty, nothing in the photo is changing.

Curves rewards practice. Start with an S curve and Drag in image, and the rest comes with use.