Say the word curves, and what do you think of? A fast car tearing down a country lane? Not me. You say curves, I say PhotoShop.
Curves are PhotoShop's most powerful tool, letting you correct colour, contrast and brightness from a single window.
But the most important thing is: Be gentle. Open the Curves window; you will see something that looks like a graph. The graph shows a straight line from one corner to the other. At the bottom is a grey scale running from white to black. The black end may be on the left or the right, and can be swapped by clicking on it. For the purposes of this article, I will assume the black is at the left.
Look for a small check box labelled Preview. Make sure that it is marked. This will allow PhotoShop to change the values of the image alone rather than change the lightness, darkness, colour, etc of the whole monitor.
Hold down the Option key on the Mac, or the Alt key on the PC, and click anywhere on the graph. The graph will become finer, with nine lines vertically and nine horizontally rather than the usual three.
Down the side of the window are six buttons - OK, Cancel, Load, Save, Smooth and Auto. The use of the first two is obvious. The second two can be used to load and save changes, should you want to apply the same correction repeatedly. This can be useful if you have several pictures shot under the same conditions which are to appear next to each other.