The New Black and White

Black and white photography has been quietly revolutionised by going digital. One way has been its easy availability — far from needing different procedures and the conscious decision before going out to shoot to load a different kind of film in the camera, black and white has become, technically at least, a post-production decision. I’ll deal with the implications of this in an upcoming Observations piece. The second revolutionary way has been the spectacular control that digital black and white now offers over the processing, and in particular over how each of the colours in the scene is converted into a tone. Any distinct colour can be reproduced as more-or-less any tone you want, from almost white to almost black.

Using the Black & White control in Photoshop, the cool and warm hues in this picture of brightly dressed women in Darfur can be virtually reversed in tone.

Digital capture is, of course, in black and white. The sensor reads light quantity, not wavelength (which is the measure of a colour), and to add colour to the image a filter array is bonded to the front of the sensor. With the exception of one particular sensor design (Foveon), this mosaic-like array has a pattern of red, green and blue filters placed individually over the photo-sites, so that each pixel is filtered with one colour only. The job of interpolating the colour across the whole image is an in-camera process, and the result is an image file — raw, tiff or jpeg — made up of three channels, red, green and blue. The value of this for black and white photography is that these three channels can be manipulated. They don’t necessarily have to be combined equally, and each one is, naturally, a monochrome channel.

In the Bayer filter bonded to the front of most camera sensors, alternating red, green and blue each filters cover one photosite. In this strongly coloured image of a bull sculpture in Chicago, the green and blue channels almost completely block the red.

Every digital image processing software, from Photoshop to Lightroom, Aperture, LightZone and others, offers a simple, no-thought, single-click method of turning a colour image into monochrome. Some offer more than one. Yet there is no such thing as a standard, ‘correct’ method, and even the most decision-free, which is desaturating each channel, assumes that the default is to treat each channel equally. In fact, there is an open choice of how bright or dark different colours will translate to monochrome. With this in mind, the best ways to use your software’s default conversion are as a quick preview and/or as a reference point against which to start channel mixing.

Channel mixing is the technique by which the three colour channels, red, green and blue, are selectively combined so that some colours become brighter, others darker, according to taste. This is nowadays presented in a very straightforward interface, in the form of sliders for each colour. The procedure is completely straightforward: select the slider for the colour you want to adjust when it is converted into monochrome, and raise it for a lighter grey or lower it for a darker grey. In most programs these are quite sharply cut filters, meaning that they tend to select the colors precisely without affecting others much (and a word of warning – extreme adjustments of sliders can sometimes cause strange breaks in tone for this reason, on some colours).

Now, simply playing around with the sliders to see what effect you can get is one way of doing this, as is cycling through the choice of presets to see which you prefer. However, a more logical, planned approach is to study the colour image first and decide what needs to be done to it. Among the many possibilities, I’ve selected three procedures….

Controlling contrast

The traditional way to adjust contrast in an image is to drag the lighter values one way and the darker values in the opposite direction, usually in a curves window, or with brightness and contrast sliders. But a subtler and more satisfying method is to take advantage of the contrast of colour within the original scene. If there are two important colours in an image that are in opposition, such as red and green, or blue and yellow, then adjusting the hues in the conversion to monochrome will easily do the trick. Raise or lower the tonal value of one colour, and its opposing colour will naturally go in the opposite direction. In the example below, a foggy sunrise offers a warm-cold contrast that can be used in this way.

The colour original, in Dedham Vale, and the default conversion in Photoshop for reference.

On the left, high contrast by raising red and yellow while lowering cyan and blue; on the right, the opposite effect, evening out the tomes by lowering red and yellow while raising cyan and blue.

Controlling depth and atmosphere

One of the most valuable hue controls in black and white photography is altering the sense of depth in a landscape shot. The technique, as old as panchromatic film, relies on blue in the atmosphere. The reason is the selective scattering of light by the atmosphere; as the bluer wavelengths are shorter, they get scattered more easily by particles in the atmosphere, and so are more visible. There are two ways to go: compressing aerial perspective by darkening the blues and so clarifying distant parts of the scene, and expanding it by lightening the blues to give a greater sense of depth.

Early morning light in this view of Pagan, Burma, is suffused with blue, and so capable of being either almost eliminated by lowering the cyan and blue sliders, or enhanced by raising the sliders. The difference in effect here is extreme.

Controlling skin tones

When most people refer to skin tones, they mean the shades of colour. Here we’re being literal — the actual tonal value, the brightness of skin when the image is converted to monochrome. Skin colours are among the strongest ‘memory colours’, meaning that we are so familiar with and sensitive to the way they should appear that the ‘correct’ appearance in a photograph is embedded in our memory. The same thing happens with a black and white image. We have a feeling for the ‘right’ tonal value. This, of course, varies greatly with ethnic group, and is not simply to do with darker vs lighter, but also involves the general colour cast. Here are two examples, one very pale, the other brown.

Very pale Caucasian skin, but the analysis shows a high red component. The default conversion is acceptable, but to my taste too light; there’s a sense of losing the highlights on the upper planes of the face. Lowering the red slider gives a more normal sense of tone, while raising the yellow slightly restores the background. This is very much matter of taste.

Distinctly brown skin — this young lady is from Eritrea. Here, the same default conversion as used above darkens the skin too much (again, to my taste). The solution is raising the red slider, while lowering the yellow to keep the background wall medium-light. Note that raising the green slider to maximum for the leaf on her forehead (there for medicinal reasons) has no effect on other colours.

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Tags: atmosphere, black & white, contrast, photoshop