CONTRAST IS ARGUABLY THE MOST important element of both black and white and color photography, and by understanding how it works and how to manipulate it you can improve your pictures beyond your wildest dreams.

Contrast basically refers to the tonal difference between the brightest and the darkest elements in the picture, and more importantly, how these are presented in the final image.

In traditional black and white photography, the aim is to present a picture where there is at least one area of the picture which is as dark as your display medium, whether it be printed paper or a computer screen, will allow and another area which is as bright as it is possible to be.

If you have achieved this, the picture is said to have maximum contrast and the image will appear punchy and alive, with very rich tones.

Pictures with too little contrast appear dull and grey and can even be described as muddy. In the days when I worked in a darkroom, I never tired of the tremendous difference between a flat, tonally poor print and that of a full contrast photograph of the exact same negative.

As with all good things in life, one can have too much contrast in ones images. If a picture is displayed with too much contrast, the detail in the lightest and darkest areas of the image will disappear into black and white. While this is acceptable for small parts of the photograph, it can be troublesome if huge swathes of detail are lost into oblivion.

There are, of course, situations where the photographer will intentionally create a lower contrast image, with whites that are not completely white or where the darkest parts of the image is toned in grey rather than in full black, but the key is to be able to get to full range of contrast from your display medium, and then break the rules if you need to do so for visual effect.

Contrast has been taken so seriously by photographers over the ages that Ansel Adams, arguably the finest black and white landscape photographer in American history, devised a system to get the maximum amount of contrast out of every single picture he printed.

The Zone System for Digital Photography

The zone system is basically a technique used to display pictures with the full tonal capabilities of the display medium. Though Ansel Adams applied the system mainly to pictures printed in a wet chemical darkroom, the system is as relevant, regardless of whether you are shooting on a digital camera or on negative, and whether you intend to display on a laptop screen or a wet chemical print.

In the zone system, the properties of the display medium are assessed, and the range of tones that it is capable of producing is divided into ten zones. The first zone, zone zero equates to complete black, as dark as you can get out of your medium, zone one can be described as near black, with detail just about visible in the shadows. Zone two would represent dark grey, while zone three holds the tones in the medium dark area. Zone four is the shades just darker than the average and zone five those just lighter. Zone six will be medium light grey while zone seven is best described as light grey. Zone eight holds all the lightest detail just visible before it disappears into zone nine, pure white.

When Ansel Adams printed his masterful work, he always made sure that each of these areas was represented in the final print. This ensured that his photographs always contained the full tonal range available and gave his images an unrivalled richness and vibrancy.

The camera’s histogram and the zone system

Every single digital SLR worth its salt has an image histogram review function.

A histogram is basically a graphical representation of the tonal distribution in the recorded image. Let me rephrase: a histogram is a graph which shows the size of the area of the image that is captured for each tonal variation that the camera is capable of recording…

Hang on a minute, that sounds an awful lot like the zone system.

In fact, the histogram is nothing more than a slightly more complex representation of the zone system. The only difference between it and Ansel Adams’ model is that it has many more zones, but they still start at pitch black and still stretch to pure white.

By looking at the histogram for a specific image you will be able to judge the entire tonal distribution at a glance. It tells you how much detail is at the light end of the spectrum and how much at the dark. It also tells you whether you may be losing detail to the outer edges of the spectrum with so-called blown-out highlights or blacked-out shadows.

By learning to read a histogram, you will instantly be able to tell whether your image is too light or dark and whether it has sufficient tonal variation to produce a good quality final image.

How to read a histogram

Like most graphs, a histogram looks much more complex than it really is.

The horizontal axis represents the tonal variations the camera is capable of recording. The left side of the axis represents the black and dark areas, the middle represents medium grey and the right hand side represents light and pure white areas.

The vertical axis, on the other hand, represents the size of the area which is captured in each one of these zones.

So let’s look at a few graphs to explain.

Each histogram on the right shows the tonal distribution for the image above it. The first histogram, with most of the weight of the graph concentrated on the left, is for a very dark, perhaps even underexposed image. The second graph, with the weight of the graph concentrated on the right, shows the tonal distribution of a light image, with very little detail on the dark side of the spectrum. The final image, with the weight of the graph distributed across the spectrum, represents a normally exposed image with a full tonal range.

Histograms, a closer look

Let’s look at one more image: the overall tonal distribution of this photograph is quite normal, though slightly weighted to the left hand side, showing that there is a concentration of tones at the dark end of the spectrum.

As you can see, certain areas of the photograph correspond directly to certain areas on the graph. The highlights in the clouds is represented by the far right of the graph; the mid-toned sky is represented by the middle of the graph; finally, the dark silouetted players corresponds directly to the left hand side of the graph.

If we lighten the image, for instance at the picture taking stage by decreasing the shutter speed, opening the aperture, or by increasing the ISO setting, the weight of the graph will shift right. If we darken it, the weight of the graph will shift left.

If, on the other hand, we increase the contrast in the image without either lightening or darkening it, such as with cameras that will allow us to adjust the contrast of the recorded image, the center of the graph will flatten out and the weight of the graph will shift to the outer edges. Do the opposite and lower the contrast and the weight shifts from the edges to the center.

The zone system in practice

Now that we understand how to read a histogram, and more importantly, how to manipulate it, we can look at the best way to get a workable image.

The central idea behind the zone system, is that you need to record all the tones needed during the picture taking stage. If they are not there, recorded by the camera, lost to either black or white, or are so densely concentrated that there is very little variation, then you will not be able to retrieve them during the later stages in Adobe Photoshop.

Sure, you may be able to lighten or darken the image slightly, but if certain details have not been recorded in the camera, they are lost forever, and there is nothing you can do on the computer to retrieve them.

At the image capture stage, or in plain English, the picture taking stage, we need to record as many tones as possible while losing as little as possible important detail to pure white or to pitch black. This allows us, during the image manipulation stage, where we edit the image in a software program such as Adobe Photoshop or Gimp, to make much more rigorous adjustments to the image without causing the tonal curve to become broken up.

That is not to say that the camera’s histogram for all images must conform to the same ‘normal’ distribution, but rather that the detail must be spread out over the entire possible range, while being weighted to the specific effect you need to create.

Say for instance you are taking a picture of people at night, outside, using flash, such as the one on the right. Here, you will not expect an even distribution. For a correctly exposed picture of the people you are photographing, you will have a tonal distribution which is heavily slanted to the left hand side, the dark side of the graph. This is because the people are surrounded by a lot of dark space, which will be lost to pure black no matter what you do. The key is to get as wide a distribution of tones as is possible for the specific detail that is needed in the final image, in our case the people illuminated by the flashgun.

You may of course be presented with more difficult subjects, where the contrast is simply too high to be recorded correctly, and this may cause clipping (where detail is lost on the outer edges of the graph to blown-out highlights and blacked out shadows). In such a scenario, you may have to resort to fill-in flash to lower contrast, or even to taking two pictures, with one exposed for the highlights and the other for the shadows.

This two step process, where you first record the widest possible tonal range in the camera, and then redistribute these tones to best effect during the manipulation stage, is the key to mastering digital photography, both of the black and white, and color variety, and any photographer would be well advised to keep both stages in mind as he presses the button to release the shutter.