Fixing underexposed shots

The two most important tools for correcting exposure problems in digital images are the Levels dialog and the Curves dialog. We’ve already looked at these in the Master Black & White book, but they’re so important that it’s worth examining them again. But what’s the difference between the two? Broadly, Levels are used for maximising the image’s tonal range, and rough brightness adjustments. Curves are used for fine-tuning the image’s tonal balance and contrast. Elements does not include Curves adjustments, so we’ll stick to describing the effects of the Levels dialog, and these are the same in both Photoshop and Elements.

BEFORE-This shot has been underexposed because the intensity of the bright white sand on the beach fooled the camera’s multi-segment exposure meter. We need to lighten the image, and the Levels dialog will tell us the best way to go about it.

The Levels dialog does indeed show us what the problem is. As you can see the tones in this image are shifted towards the left-hand (shadow) end of the scale, and the histogram tails off long before the right-hand (highlight) end.

‘Clipped’ shadows

Digital cameras can’t record an infinite range of tones. If the darkest areas of a scene fall below the sensor’s detection threshold, they’re going to record as a solid black tone with no discernible image detail. This is what’s called ‘clipped’ shadow detail, and it’s more common – obviously – with underexposed images. The histogram in the Levels dialog demonstrates this visually – the ‘toe’ of the histogram is chopped off abruptly. No amount of adjustment can restore this clipped shadow detail – it’s gone for good. What’s more, you need to be careful, when making Levels adjustments, that you don’t clip even more detail.

AUTO LEVELS-The Auto Levels command can often fix an image instantly. You’ll find it on Photoshop’s Image > Adjustments menu, but it also has a button in the Levels dialog. Our shot looks much better after we’ve applied this command.

LEVELS-The Auto Levels command can be effective, but like all automatic tools, it’s not foolproof. What’s more, because it adjusts each colour channel individually, it can cause colour shifts. Manual Levels adjustments will yield more controlled results.

The Auto Levels command has stretched out the histogram so that it now reaches the right-hand (highlight) end of the scale. The image’s tonal range now stretches from dense blacks to brilliant white highlights.

You adjust the Levels manually by dragging the sliders under the histogram. Here, we’ve brought the highlight slider back to just the point where the histogram ends. We’ve also moved the mid-point slider to the left to slightly lighten the image overall.