Getting the right level and type of tonal contrast in a finished image is something a lot of photographers find challenging. Very often, in an attempt to generate a bit of impact, the contrast slider is dragged up the scale until dense shadows and over-bright highlights appear to deliver the ‘woof’ that’s required.
However, in many cases, by the time the desired effect is achieved the shadows and highlights have begun to conceal information rather than helping with the story. As well as hiding details, deep shadows and very bright whites often create a distraction of their own and draw the eye away from the subject. It also makes the photo look less realistic.
The secret to boosting impact in an image without compromising detail is to use the curves tool. Contrast sliders are blunt instruments by comparison and deal only with the extremes of the tonal range, while a curve allows the photographer to determine which tonal values get the separation that enhances the feeling of depth and three-dimensions in the picture.
For an image where the exposure is about right for the main subject, try just a slight tweak of the curve in the middle of the line. This will create an exaggerated difference between the greys just below the mid tone, and this is often enough to lift the image sufficiently to create some impact. Lifting of the brighter tones and the darkening of the darker tones will have more dramatic, and you only need to apply small changes to see the effects at play.
The impact comes about relative to the incline of the slope between the two points, and the steeper the curve the more chance there is of losing the darkest and brightest tones to deep shadow and burnt-out highlights.
Sometimes the contrast is needed in a specific tonal area – for example, if you are trying to separate a medium grey tone from a dark grey. With the curves window open in Photoshop, we can use the curser to click on areas in the picture to find out which part of the curve line relates to each tone. Then we can create the curve in that area by dragging one tone down and the other up. This way we only create contrast in the tonal regions that need it and we get to hold on to the extreme tones without them becoming featureless areas in the image.
Other times, we need to use restraining points to prevent the extreme tones from being too dramatically affected by our local adjustments. If a shadow area curve has forced the highlights to become too bright, create a new control point and pull the line down a bit. This creates an uneven curve, with is generally not a good thing, so keep the corrections moderate.
Quite often it is a dramatic reduction in global contrast that is needed to make a subject stand out more, and then a small tweak to a curve to add impact to the tones that need separating.
Impact comes about not just through the addition of contrast, but through the addition of contrast in the tonal areas that need it. With the curves tool and with practice, you can refine your images to strike the right balance and create visually striking images.