When a photograph is converted to mono and the colour removed, what remains is tone. Tone is in fact one of the reasons black and white photography has continued to be popular after the advent of colour. It was the tonal quality of Paul Strand’s work that inspired landscape legend Ansel Adams to make a career change from classical pianist/bobby photographer as a hobby to full time professional. It was the“full, luminous shadows and strong high values, in which subtle passages of tone were preserved” in Strand’s photography that Adam’s found so compelling.
Tonal range refers to the range and distribution of tones in an image from the darkest to the lightest values. An image with a wide tonal range will include very dark (black) and very light (white) elements, whereas as one with a narrow tonal range will be limited to a more restricted area and will have less contrast. Lighting conditions have a great impact on tonal range. On a misty day in Oxford, UK the difference in brightness between the lightest part and the darkest parts of the scene will be relatively insignificant, but under the harsh light of the mid day sun in Arizona the range will be much greater. Extremes such as that aside, images with a wide tonal range tend have both greater contrast and greater appearance of drama and depth. A narrower tonal range makes the image look flatter, though this may be by design. Tonal range is influenced by the amount of and quality of light (harsh or soft) and the reflectance of the subject. The addition of a polarising filter, something I use extensively, improves contrast and can thus help expand the tonal range. Tonal range is different from dynamic range which refers to the ability of the camera’s sensor to capture shadow detail from the darkest values and highlight detail from the brightest values in the same shot. Dynamic range is maximised in RAW format which records all the image data the sensor is capable of recording, and is one of the main reasons this format is used. Cameras.about.com describes the the tonal range of a digital image as “the number of tones it has to describe the dynamic range”, which helpfully describes the difference between the two.
Tonal contrast is created when light tones and dark tones are adjacent to one another – it has the effect of directing the viewers attention to the contrasting area and is the basis of the success of many black and white images. It is an essential element of composition, but is not as well known as other compositional rules such as leading lines, the rule of thirds, framing, and diagonals.
A tonal curve is typically applied to the image by the camera by default as the image data from the photo sites is linear (the values are directly proportional to the light received), whereas human vision is non-linear. The process is known as (tone curve correction aka gamma correction) and makes the pictures look right to the human eye on a screen display. This process generally lightens the midtones. This default tonal curve can be adjusted in the curves tool of RAW conversion programs (such as the ageing but excellent Aperture, which I still use). The Aperture user manual describes the use of the Curves tool quite well:
“You use the Curves adjustment controls when you want to manually set the tonal values of the shadows, midtones, and highlights in an image using a tonal curve. Unlike the Levels adjustment controls, the Curves controls do not reapportion the luminance values in the image by constraining the white and black points. Instead, you use the Curves controls to precisely remap the position of the midtones relative to the white and black points. Because the human eye’s perception of light is logarithmic rather than incremental, a curve is necessary to distribute the luminance values across all tonal ranges in an image in a way that matches how the eye perceives light in nature.”
Applying an S-shaped curve to the data, which is initially shown as a straight line, applies a steep curve in the mid tones, which increases contrast and give the image greater impact. A correctly exposed film image has an inherently more S shaped tone curve than a digital image, and film, being based on a chemical process, and therefore essentially analogue, also creates a smoother continuum of tones than digital cameras. This difference diminishes with every generation of sensor. As much as I care about tone, the advantages of the digital dark room, for me at least, vastly outweigh any disadvantages of digital photography. Let’s take the example of dodging (applying reduced exposure locally) and burning (applying additional exposure locally), both of which are important techniques to modify tone. To quote Ansel Adams once again: “dodging and burning are steps to take care of mistakes God made in establishing tonal relationships.” Both are fiendishly difficult to master with film to the level Adams used, and far simpler with image editing programs such as PhotoShop. It is worth noting that some photographers also consider that dodging and burning can give a more natural impression than adjusting the tonal curve. I use both techniques.
Here are some of the advantages that the various attributes of tone confer over colour:
- With only tones to work with, black and white forces the photographer to pay closer attention to composition – which is in itself an advantage.
- The simplicity of a race of tones makes the subject easier to focus on, which is one of the reasons so many street photographers eschew colour.
- Simplicity can be enhanced by discarding extraneous detail more easily in monochrome images. I often burn out distracting detail in dark areas to further simplify the image.
- Editing a photo converted to black and white provides a much greater opportunity to redistribute the light to create finely graduated tones, which can make architecture and sculpture both more three dimensional and more beautiful.
- In portraiture, skin tones are evened out.
- Graphical elements and patterns are more evident.
- Abstract images are stronger.
- Textures often appear to have more depth.
- Black and white photography is more effective in low contrast situations, such as under heavy cloud
My example of tone from Flash of Darkness is the Colossus of Constantine in the Courtyard of the Palazzo dei Conservatori of the Musei Capitolini (Capitoline Museums) on the Capitoline Hill in Rome. The statue, built c. 312-315 AD is truly immense and once stood at around 40 feet high. I have experimented with many different versions of this image, from low key to high key and with varying tone curves and application of dodge and burn. The image I prefer however is the one on this page which is fairly neutral, with only a slight increase in contrast; it seems to be the most effective at describing the shading of the marble forms and the subtle changes in the tones of the painted plasterwork.