Curves adjustments are one of the more advanced image-editing techniques, not because they’re especially technical or difficult to carry out, but because you have to understand exactly what’s happening in order to make any genuine improvements. With curves, a small adjustment can make a big difference, and Aperture curves adjustments are no different.
Curves work in exactly the same way in any image-editor that offers them. Initially, the image ‘curve’ is a straight line running diagonally from the bottom left corner of the scale to the top right. The curve matches ‘input’ and ‘output’ levels, so that when you start out, the input brightness is the same as the output brightness, hence the straight-line graph.
But by changing the shape of the curve, you can change the way different parts of the tonal scale are reproduced. You can make shadows darker, highlights brighter and, where you create a steeper section of curve, you can increase the contrast.
So understanding how curves work is only half the battle – you also need to be able to assess your pictures to see exactly what kind of adjustments are going to produce the best results. And to show how this can be subtly different from one image to the next, I’ve assembled three pictures I took at an air show just a few minutes apart.
This is one of them. It needs a subtle boost in contrast, but as we’ll see it needs to be done in the right way, and what works for one image won’t necessarily work for another.
01 The Aperture Curves display
You’ll find the Curves panel amongst the tools in the Adjustments panel on the left. If you don’t see it, you may need to open the Adjustments menu from the top and choose it from the list. To start with, all you see is this straight line against a blank background.
02 Curve control points
To change the shape of the curve you just click on it. This adds a control point which you can then drag up and down vertically to make that section of the curve lighter or darker respectively. (You’ll see that the curves panel now displays a histogram behind the curve to help you judge your adjustments more effectively.)
Here, I added a control point (1) near the bottom of the curve, in the shadows region of the tone curve, then dragged it downwards to make the shadows darker still. Then I added a second control point (2) near the top of the curve, in the highlights region, to make the highlights brighter still.
You’ll see that the section of curve between these two control points is now a lot steeper, which means the contrast in this region is now higher. And you can see this in the picture, which now has a lot more contrast in the midtones, right where the curve has become steeper.
This is the classic ‘S-shaped’ curves adjustment used to boost contrast in flat-looking pictures, and it’s certainly improved this one. The tones in the shadows are now darker and more flattened out, and the highlights are brighter and flattened out too, but that doesn’t matter because the midtones, where all the detail and interest lie in this picture, are now much more vivid.