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Digital Contrast Management We have all heard the saying "the sky is the limit". Is it really true? In this article, I will discuss digital contrast management. As most advanced photographers know, a film can only record details in a certain range of contrast. Details in the very dark shadow areas become too dark to discern, and highlight details in the bright areas become blown out. Details which we perceive with our eyes in the orginal scene is not a accurate representation of how it will turn out in the final image, because our eyes can adapt to a great range of contrast than the film can. Conventionally, there are several ways to combat this deficiency of film. All depends on the photographers' ability to analyse the brightness range in the scene prior to exposure. The basic theory of controlling contrast lies in reducing light in the bright areas, and/or increasing the light levels in the shadow areas. You can use a neutral-density (or coloured) graduated filters to bring down the brightness of the skies, or use fill-in flash or reflectors to boost the light levels in the shadows. I am a great proponent of doing things right the first time round. If it can be done conventionally during exposure, do it. If I face a high-contrast scene, I will try to balance the contrast in the scene with the above tricks such as fill-in flash and reflectors. But what if I do not have any of the tools (such as ND-grad, flash or reflectors) with me? Or perhaps it is impossible to fill-in a huge dark area? Do I skip photographing the scene altogether? No! There are various ways of coping with such high-contrast situations in the conventional (non-digital) ways. B/W photographers have the old adage "expose for the shadows, and develop for the highlights" to gain maximum details from the negative. Others might take two images (one exposed for the shadows, the other for the highlights), and merge the two images in the darkroom manually. This article will teach you some simple ways of controlling the contrast so that the skies and land can be represented equally using digital techniques. Of course, I am using the sky as an example of high-contrast area, but you can apply the techniques learnt here to other scenes with high contrast.
Scanning same image twice This is probably the easiest digital manipulation to do. If your original image has areas which are not too severely overexposed/underexposed, you might be able to create a optimal image by scanning the film/negative twice. The idea is that the film contains the details in the highlight/shadow areas, but you cannot fit them into the tonal scale of the paper in a straight print. As such, by scanning the same film twice (once for the highlight details and once for the shadow details), you can extract all the details and merge them together into the same print. Conventional darkroom printers can do exactly the same thing through a process called dodging and burning. Because we need the details, you need to be able to scan from the film
using a film scanner. Alternatively, you can also make two prints, one
for the highlight details and one for the shadow details, and scan them
using a flatbed scanner.
Once you have scanned both images into the computer, open up both files simultaneously in the imaging program. Select a broad brush and select a point for cloning (it is ALT-click for PhotoShop) on the image with the highlight details. Next you need to go to the image with the shadow details (making sure that the cloning tool is selected) and start painting over the highlight areas (those areas which are blown out). The cloning tool will copy the area of the highlight details onto the current image. If your positioning of the cloning tool is correct and the image size of both images are the same, you will be able to achieve a precise match of the two images. You are using the broad brush now to clone the image area, for maximum speed. When you are nearly done with cloning most of the areas, switch to a small brush to clone in the edges. This will allow you precision cloning for the narrow areas. When you are done, the image will contain both details in the highlight and shadow areas, just like your eye saw them in the original scene.
Shooting two exposures to shoot two exposures: one for the highlight, and the other for the shadow. Try to use a tripod for this purpose, because it allows you to shoot twice with exactly the same viewpoint. You might ask, "how the hell do I spot meter for the highlight and shadows if I am not allowed to change my viewpoint?". Simple, you meter before shooting the two frames! Once you have shot the two frames, scan them and scale them to the same
size. This is crucial if you are to match the two images. This technique
is similar to the one above, but now you are scanning from two images which
are optimized for the shadow details and highlight details, giving you
the best results. Once the images are scanned, open them up simulataneously
and do exactly the same thing as the technique described above.
In case you are wondering why you must shoot two frames when I said
you can use the first method of scanning the same frame twice. It is because
the first method is only applicable if the highlight and shadow areas are
not too extreme. In case of extreme situations, this method of two exposures
will work much better than the first one.
Combine the sky from another image digitally This technique is slightly tricky, but it is not difficult to do. The trick is to add in a sky from another scene to replace the blown-out sky in your image. What can be so difficult about that? The new sky which you are adding in must match the required area to
be filled. And the most important rule is that the new sky must match the
direction and intensity of the light in the original scene. Otherwise the
montaged scene will look surreal and unnatural.
Like the technique above, you are required to scan both images and use
the cloning tool to clone in the image for the highlight areas. The only
difference is that you are working with two different scenes rather than
two scans of the same scene. Match the areas carefully, and nobody will
be wiser for the fact that it is actually a manipulated image!
Draw your own skies This is perhaps the most drastic measure of all. If you did not photograph the original sky, have no matching images of sky, and you are unable to scan the original film for details of the sky, then you need to get creative and draw your own sky! I have used the image of two adjoining brick walls as an example. The
original image was taken on a overcast day, resulting in an overexposed
sky and bland looking red brickwalls. I adjusted the contrast and saturation
of the walls to give them more "umph", to match the cheery blue sky I am
about to add.
Next, I selected the white sky area with the marquee tool, carefully trimming it with the magic wand tool to get the exact area. Once I was satisfied the selection, I chose two pale shades of blue from the colour palette, one of which is slightly lighter than the other. You need to posses a keen sense of observation to choose colours which are realistic to match nature. Next I used the gradient tool to fill in the sky, creating a smooth bland of blues. The reasons for using a gradient of blues instead of using a paintbucket of blue is because most skies are at least slightly graduated and not just comprising of a single shade. Without deselecting the area (I'll tell you why in a moment), I selected a very pale blue which is nearly white. I use the spraypaint tool and a wide soft-edged brush to paint in the cloud. I did not use pure white paint because most clouds are slightly bluish. Because you are trying to create a false sky, you must be very careful about such details, otherwise the image will look very fake. Do not worry at this point that your clouds do not look real. Now use the Gaussian blur tool to blur the sky with the clouds. The reason why I told you not to deselect the cloud is because you have to blur the sky area without affecting the other parts of the image. Adjust the level of blur with the slider, and the cloud will immediately look much more realistic! Do not try to increase the blur factor too much, or else the edges of the selection will start to halo. A slight halo and blur acts to make the image more believable, since a hard-edged wall looks fake. The image is now completed, and you have a much better looking image than you started off with! Enjoy your new found tool! All text and images
by Nelson Tan
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