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Taking Photographs

(7 - The Evolution - Exposure & HDR)or Back to Table of Contents

We've looked at histograms to see how exposure was working when we photographed our images. In short if information was flowing off the sides of the histogram, then we were losing information. There are certainly times when having an ultra-dark image or an ultra-light image may be desirable. Some artistic types create what's called a "high-key" image. These are bright and happy images of maybe a white subject on a white background and very low contrast to everything else. Occasionally they can be over-exposed for effect. This isn't a bad thing. Additionally, some create images in dark shadow where only the highlights of the subject can be seen. For artistic effect these work.

Sometimes one is not being artistic and the image is still exposed incorrectly. There are complicated scenes that many cameras still cannot do, even in this modern age. This is important because unsatisfactory images sometimes are not the photographer's fault. They may be the limits of the modern hardware and software. What can't be captured? Suppose one has a super bright area in your image and a super dark area too. Take a look at the example image below. The bright sky and the darker mountainous area are in great contrast. Only one of those areas is going to turn out satisfactory because the camera can't do both ranges. The human eye will dart around a scene to get the detail but your camera can not.

Having an image with two super contrasts of both light and dark in it will make it hard to find the balance. This is true with the histogram below. It is apparent that the sky was so bright that it washed out the image on the top. That information is lost and much of the details in the clouds are gone. As the photographer this image may look okay but one must be aware of the problem and maybe accept the trade-offs depending on the situation.

When the photographer sees over exposure in the camera's histogram they shouldn't be afraid to crank the manual exposure down on the camera. If not sure how to do this, then it is really worth looking up the camera's manual. On a Canon it often means holding the AV button and turning a dial down. This setting tells the camera that I don't need as much light from the aperture in the lens.

Histogram to image number 1

The image 1 above is over-exposed in the sky area and clouds have no detail

In the image below we've taken the same seen and lowered the manual exposure in the scene as the image was taken. What we get now is a crisp sky with detailed clouds. The trade-off is dark mountains but the histogram shows that we have not under exposed the scene. This is a good sign that other adjustments are possible later in our processing software.

Histogram for image 2

Image number 2 is dark in the mountainous area but not under exposed.

One solution for capturing a high contrast scene that may have the extremes of both dark and light is to use a polarizer. Circular polarizers can help cut down the light in certain circumstances. They mostly work if the sun is shining 90 degrees from where one is focusing. So using a polarizer and the sun is straight in back of the photographer then it won't help much. However, if the sun is coming from your left or right and you turn the polarizer the results are quite remarkable.

There are other tools out there to cope with scenes where extremely bright lights and very dark shadows at the same time. One of these is a neutral density filter. These are a bit like putting sun glasses on the camera lens. They are created not to change the color of your image. However, they do reduce the light and make the camera take longer to get the light needed. If the camera needs too long to get light then you may also need a tripod to get a clear scene.

A new trend is HDR or High Dynamic Range imagery. Many cameras now come with what is called auto exposure bracketing. This means the camera is prepared to take 3 shots for every image you want to take. Usually you have to press the button on the camera three times yourself unless you use the timer or a remote control and tripod. The camera then takes a dark image (under exposed on purpose), a bright image (over exposed on purpose), and then a middle range image. The HDR software out there now takes the brightened details in the shade and the darkening details of the clouds and sky for a hybrid image. The results are incredible in many cases and sometimes artsy depending on how they are processed. Many believe that this HDR process will soon be a standard feature process in-camera that each hardware can do. This idea may be a some time down the road.

You can still create the perfect image if you take auto-exposure-bracketed (AEB) images and don't buy the software. In Photoshop, GIMP, or other image editors you can place all the exposed HDR images on a different layer. You will have to become comfortable with how layers work before you do this. It is then possible to remove the poorly exposed sky to show the betters sky from the best sky image. Using layer masks and so forth you basically splice the best parts of all three images together. The Franken-image effect can be surreal but cool in appearance.

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Written March2008 and updated Dec2010 by - Tracy Lee Rose