The picture of the lighthouse was taken after sunset on a cloudy day. The contrast is very low, with the tonal values in the histogram lying primarily in the middle. Information: 65 mm | f7,1 | 1/60 s | ISO 400 | APS-C-Sensor
Contrast refers to the distribution of brightness in an image. If the contrast of an image is low, or "soft", the tonal values are clustered within a small area and are difficult to distinguish from one another. With colour photos, the colour mood means that a low contrast may not be noticed. Black and white photos generally appear dull if the contrast is low, unless the tonal range lies primarily in highlights (high key), or in shadows (low key).
Black and white photography rarely has the problem that the contrast is too high or too "strong". With colour photography, by comparison, the colours appear unnatural if the contrast is too strong. With black and white photos it is even possible to clip the highlights or saturate the shadows, provided this fits with the content. Generally speaking, however, you should take care to ensure that the tonal range in the image is not exceeded, with the exception of small highlights. You can control the contrast of black and white photography to a large extent. Whilst you have few options to influence the production of black and white pictures, those that you have give you considerable room for manoeuvre.
The pickup truck sits in the harsh midday sun in southern France. Glistening sunlight and deep shadows produce a strong contrast. The histogram uses the full tonal range, and has points at the ends. Information: 20 mm | f11 | 1/200 s | ISO 125
The photo of the lighthouse has been edited to make full use of the contrast range. The clouds, barely visible in the first version, now stand out clearly.
Gradation refers to how steep the brightness curve of a tonal value climbs. When analogue cameras were used, gradation could be controlled though the development of the film and the choice of photo paper. If a film was exposed for longer and then developed quicker, the negative would be softer (have a lower contrast) than if the film was under-exposed and developed for longer (known as "pushing"), because doing so enabled the sensitivity to be increased.
There were also paper types ranging from gradation 0 (very soft) to gradation 5 (very hard). This meant it was possible to balance out a soft or hard negative using the paper, but also gave significant scope for choosing different contrasts. With digital photography you can adjust the gradation whenever you want. If you use Photoshop to 1) strengthen the shadows and 2) reduce the highlights (Image • Corrections • Gradation curves), you will notice the middle of the gradation curve is flatter than the 45° degrees of an raw curve- the image appears soft and low in contrast.
An uncorrected gradation curve represents each tonal value as itself, and changes nothing. You are able to adjust a gradation curve considerably and in many different areas. Doing so can also quickly ruin a picture, however. If different tonal values are represented as the same value, for example, the image no longer appears photographic.
If you strengthen the highlights and reduce the shadows (3), the curve becomes steeper and the picture stronger. Since you have not changed the end points, the contrast range remains the same, which means the highlights will not be overexposed and the shadows will not be saturated. The control options are considerably easier than in analogue photography.
The gradation curve lets you control the contrast of your images, just as you could before using paper gradation. The 45° line corresponds to normal gradation (1), the curve with strengthened shadows and reduced highlights has a "soft" gradation (2), and the curve with the reduced shadows and strengthened highlights has a "hard" gradation (3).
Improving Partial Contrast
Partial contrast refers to the contrast of different image areas with one another. It is important for differentiating image elements and ensuring the picture has a good overall impression. You can increase the partial contrast by increasing the contrast of the image as a whole. This may lead to the overall contrast appearing too strong, however.
The example image (4) is a view of the Majorcan coastline. On the day the photo was taken there was a slightly stormy atmosphere. The aerial perspective means the individual headlands in the picture appear lighter and lighter the further back they are. The different sections in the middle cannot be distinguished from one another, however easily, and the image appears a little too soft.
In image (5) the gradation has been increased and the separation is now fine, but the original atmosphere has been lost. There are hardly any outlines in the sky and the image has become a little too hard. Whilst it still works as a photo, there is now a different mood.
In image (6) the partial contrast is as high as in the second image. The overall contrast, however, is only a little higher than in the first image. The atmosphere is retained, whilst the differentiation between black and white has been improved. How can you achieve this effect? To do this you need an increase in the local contrast without changing the overall contrast substantially. The technique is known as "unsharp masking" – it is a Photoshop filter that is rarely used. A small radius of 0.8-1.5 pixels and a strength of 150% (typical values for image sharpening, the standard use of this filter), will produce significantly sharper edges.
If instead you choose a very large radius and select a low strength, you will increase the partial contrast. The radius must be large enough that it is no longer seen as a glow along the edges. In this example a radius of 100 pixels was used, together with a strength of 25%. These values are based on an image size of 3 megapixels. With larger pictures it may be advisable to increase the radius further.
The first image appears quite dull. Raising the contrast as a whole leads to overexposed highlights. If you adjust the partial contract using the method shown here, however, the picture elements distinguish themselves from one another much better, without the overall contrast creating problems. Information: 190 mm | f6,3 | 1/1250 | ISO 100
During the analogue enlargement of a black and white photograph the light of the enlarger is often shadowed in certain areas (a process known as dodging), whilst other areas are over-exposed. This provides an extensive range of options to control the tonal values, and harder photo-paper can be used to bring back the shadows and highlights into the tonal range of the paper. For digital photographers it may at first appear somewhat paradoxical that burning makes the image darker, and dodging brighter. The analogue process of developing black and white photos is a negative technique, however. After development, the silver will become dark where it has been exposed. In this way, a film negative exposed on negative paper will produce a positive. In Photoshop you have both a dodge tool and a burn tool at your disposal. For photographers who have experience of working in darkrooms the symbols are almost self-explanatory. The dodge symbol looks like a cardboard stencil on wire, with which you can cover certain areas of the picture to make them brighter. The burn tool is a hand in the shape of a hole, which can be used to add extra light to selected areas following the standard exposure time.
This photo has been filtered in yellow using Photoshop, but the tonal values are still not ideal. Information: 135 mm | f8,0 | 1/320 s | ISO 100
In this second version the sky and parts of the church have been burned, while the shaded areas have been gently dodged. The tonal values appear to be more harmonious.
In contrast to the darkroom, Photoshop allows you to limit the sphere of influence of the tools to dark areas, mid-tones, or highlights, though the tools do have the disadvantage of producing a slight "painted" appearance. You should therefore set the EXPOSURE to a low percentage (5-12%), and go over the areas you want to change carefully a number of times. The tools can be graded even more precisely if you use a graphics tablet with a touch-sensitive pen rather than a mouse. Even the cheap amateur equipment (like the Bamboo range from Wacom) is much better than a mouse. Another method that can be used to change the brightness of image areas is to select a smooth area and then darken or brighten this using the gradation curve. This technique is preferable when working with larger image areas because it is easier to create a natural impression.
In the example image the area of the stone was selected using the polygon lasso tool, it was then FEATHERED to a width of 120 pixels, and a new adjustment level for the gradation curve was created. The corresponding areas were then darkened there. To see in detail how these production steps are undertaken in Photoshop, you can follow a practical example in the next step.
The light stone in the left foreground of this picture draws the attention of the viewer too strongly. It should be darkened, so that the church tower plays a more prominent role in the picture.
The picture has been partially darkened using an adjustment layer, and has been changed to black and white using another. This approach leaves you free to use other editing options, because the original data is always retained.
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