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Most of the better image editing programs, including Paint Shop Pro, PhotoImpact, Photoshop Elements and of course Photoshop itself, also include another way of altering brightness and contrast, but this time with more subtlety and control, by adjusting the levels histogram.

You’ll usually find this in the same area of the menu as Brightness/Contrast. In Photoshop Elements 5 it is in the Enhance menu under Adjust lighting, whereas in Paint Shop Pro X it is in the Adjust menu, under Brightness and Contrast.

The levels histogram is basically a graph showing the proportion of pixels in the image at each colour intensity. The far left-hand end of the graph represents black, and the right-hand end is white, with every tone in between represented by a spike on the graph. On the bottom axis of the graph are three points, the left representing the black cut-off point, the right the white cut-off point, and the one in the middle representing the mid-tone point.

As you can see from the graph here, our image is all highlights and shadows, with very little in the mid tone range. What we need to do is brighten some of those shadows into mid-tones, so the way we do this is by moving the mid-tone point left towards the shadows.

As you can see this has the effect of bringing out a lot of the detail from the shadow areas without burning out any more highlights. It also leaves the deeper shadow areas intact. It is a far better way of adjusting the exposure of a photograph than simply altering the Brightness/Contrast, however it isn’t quite the best way. Adjusting the Levels mid-point is still strictly linear in its adjustment. For the best results you need to be able to make precise adjustments of specific tonal values.

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