The curve tool is essential when it comes to contolling the colour and tone of an image, don’t be afraid of this feature of Photoshop –

Once mastered, you will gain precise control over your work!

The curves command works around a graph, Original image against New image with variations being made to the shadows, midtones and highlights of the image. Default setting is RGB, so all channels will be changed at once; This tutorial will only deal with RGB curves – not colour correction with the curve tool.

How To Read Curves

It doesn’t take long to get to grips with the ideas and concepts of what you can do with this tool, here’s a quick-start guide on the basics:

Vertical axis shows the new values for the selected band.
Horizontal axis shows input levels and tones from the original image.
An image in its original (unaltered) state will have a straight line of 45deg.
Bottom left is your pure black point, top right is your pure white point.
Important – Always make your curve adjustments via Layers > New Adjustment Layer > Curves rather than simply Image > Adjustments > Curves, so your curve can be edited later in your creative process if needed.

Creating A Simple Curve Adjustment

Create a new curve adjustment layer. Now, you need to add a ’point’ before you can use the tool, so left click on the line once to create a point like this:

Refer to the top image for what the regions are – my point is in the shadows. This point can now be dragged up or down, moving it up will make the selected tone brighter, moving it down will make the selected tone darker. Here’s an example of a curve you might use, with several points on it:

Practical Example Of A Basic Adjustment

As with any tool, the more you use it the more you will get to understand and appreciate its subtle (or drastic) effects. Here is an example of a basic shadow/highlight correction on a stock image. The curve adjustment looks like this:



Small changes on the curve make BIG differences to the image – so be subtle with your use, a selected point can be moved with arrow keys if more precise adjustment is needed. Subtlety is very important, big changes can cause very un-natural looking products.
If you need to reduce the effect of the curve so it only partially affects the image below – just lower the adjustment layer’s Opacity level in the Layers Pallet.

Quick Fixes

Increase Brightness – Make a point near the middle of the line and move it up slightly to increase midtones.
Decrease Brightness – Make a point near the middle of the line and move it down slightly to decrease midtones.
Decrease Brightness And Contrast – Drag the pure white point (top right corner) down the side of the graph.
Made a Mistake? – While still in the curves window, hold Alt. The cancel button changes to reset, allowing you to restore original settings.

I hope this brief and simple guide to curves helps some of you out with your photography and digital art. If you would like further information or help understanding aspects of this topic, please post in the Tutorial Talk Forum.


About the author:

I live in Northern Ireland, currently still in school studying to do Sonic Arts at university. Enjoy photography (Nikon D70) and Photoshop (Cs), aswell as playing bass in jazz bands and singing choral/classical works.
Check out my Profile/Gallery for more tutorials and to see my work.