Most digital photographers are using level adjustments and/or curve adjustments to adjust and improve their images, but how are curves different from levels, and when should you use them ? This tutorial will help you understand a bit more about curve adjustments in photoshop.
If you’re comparing the curve adjustments with level adjustments, level adjustments are more straightforward. You use it to give your images the maximum possible contrast by making sure that the darkest parts correspond to dense black, and the lightest parts correspond to brilliant white.
What about Curve Adjustments?
With Curve Adjustments you can increase the contrast in flat-looking images, lighten dense shadows withouth bleaching out the highlights in the image and also darken and saturate pale colors. You can also save curves for re-use if you have several images with a consistent color bias or lack of contrast.
Like Level Adjustments, curve also can be applied directly to image layers, and they can also be applied as adjustment layers. Here are some samples og curve shapes and their uses, plus ways to adjust parts of your image only using adjustment layer masks.
Using Curve Adjustments to Darken and Lighten an Image
You can drag the centre of the curve upwards to increase the lighteness of the image in the midtones without loosing any shadow or highlight detail. Of course, if you need to darken the image, what you need to do is to drag the center of the curve downward.
Using Curve Adjustments to Increase the Contrast of an Image
The steeper the curve, the greater the contrast becomes in that section of an image. By using the mouse pointer over the sky shows its position on the curve. If we steepen the curve at that point, we increase the contrast in the sky.
Using Curve Adjustments to Avoid Blown Highlights
When you adjust one part of a curve it tends to have a know-on effect on other areas. But we can lighten this image overall, while keeping the highlights unchanged by ‘pegging’ the curve about three-quarters of the way up
Using Curve Adjustments to Adjust Individual Channel
The Curve Adjustments are applied to all three color channels (RGB) in an image so only brightness/contrast distribution is altered. But if you want, you also adjust the RGB channel manually by choosing the one you want from the drop-down menu. In this image, I want to warm-up my image by lowering the blue curve
Using Curve Adjustments with Black and White Points
You can use the curve just like you use the level adjustments by using your image’s black and white points. This is how you do it, click the option button, and you can choose how much you want to clip the shawod or highlights to maximise contrast. A small sacrifice in one or the other can boost the contrast markedly.
Using Curve Adjustments with Curve Eyedroppers
You can maximise your image’s tonal range and fix color cast at the same time using the curve eyedroppers. They do the same thing as they do in the levels dialog. What you’re doing is setting neutral white and black points, and this usually shifts the color to some degree. I’ve found this technique is really useful when you want to have a product shot with a clean white background while you can only afford a (not so) white background.
Save Your Curve Adjustments setting
If you certain characteristic curve shapes that you’ll use quite often, you can save your curve setting and apply them to different images
Adjustment Layers > Curve Adjustments
Instead of using your curve from image adjustments (image>adjustments>curves), you can change your curve via a curves adjustment layer (layer>new adjustment layer>curves). You will get the same curves dialog and control, but you can go back later and change any of them. The benefit of using this technique is you can change any of your setting without changing the image pixels themselves (non-destructive).
When you create a new adjustment layer, it comes with a ‘mask’. Initially this is a clear, but if you click on it and paint it over black, it hides the effect of the layer where you paing, letting you control the areas of the image the curves adjustment’s applied to. You can also repaint your mask as many times as you need to get it right.
See also: Photoshop Tutorials