Controlling contrast: levels and curves

Successful black and white photography relies on careful tonal adjustments. With film photography this is achieved initially by selecting the correct exposure and contrast filters to help separate and distinguish the images tones, and then by careful selection of paper grade (contrast) and print exposure time. In the digital darkroom, we can simulate filters using the Channel Mixer, as weve seen, and the Levels and Curves dialogs enable you to make extremely precise contrast and tonal adjustments. Whatever you do, dont be tempted to use Photoshops Brightness/Contrast controls; this is like using a sledgehammer to fix your wristwatch, and youll end up deleting vital shadow and highlight detail, and ruining your images. Instead, your first stop should be the Levels dialog, which tells you exactly how the tones in your image are distributed, and enables you to adjust the contrast range exactly, producing the brilliant white highlights and dense black shadows that most black and white shots rely on.

AFTER-The histogram in the Levels dialog shows us that the tones in the image tail off well short of the highlight end of the scale. We were able to drag the white point slider to the left to restore a full range of tones.

BEFORE-This shot was taken in brilliant tropical sunshine, but its come out rather dull and muddy-looking. This was no doubt due to the cameras meter being fooled by the bright sand, but what can we do about it?

Controlling the highlights

Sometimes black and white images will look dull and flat, and the Levels dialog can provide the solution. We looked at the Levels dialog in relation to colour images in Chapter 2, and the principle is exactly the same for black and white images. The histogram displays the distribution of tones in the image as a histogram, which displays how many pixels in the image correspond to the different brightness levels, ranging from pure black (far left) to pure white (far right. The most common cause of a dull-looking black and white image is the absence of pixels at the highlight end of the scale, indicated by a histogram curve that tails off to zero before it reaches the extreme right-hand side of the scale. You can fix this by dragging the white point slider to the left until it meets the point where the histogram tails off; this expands the images tonal range to include all values up to a brilliant white.

LEVELS-The white point slider is the right-hand one of the three sliders directly below the histogram; by default, it will be at the far right end of the scale. The knack is to drag it until it meets the right-hand edge of the histogram.

CURVES-You can achieve a similar result using the Curves dialog; by pushing the centre of the curve upwards weve lightened the image overall, and compressed (flattened) the highlight area.

Next >>