High Dynamic RangePhotography is all about light. Except when it isn't. Sometimes a camera will manage to capture the delicate balance of light and shadow just with its automatic settings and create an image of breathtaking clarity and tone. Sometimes. All too often, however, part of the image will be over or under exposed. Digital photos with a lot of sky often have this problem. Either the sky is in focus and colored correctly leaving something in the foreground a black silhouette or the foreground is exposed correctly and the sky is a white, washed out mess!High dynamic range (or HDR) is a way to work around this. The concept is very simple if three different exposures of the same photograph are taken they can be merged digitally to bring out the correctly exposed areas of each photograph. A feature of many DSLR cameras and some medium or smaller format cameras is called Exposure Bracketing. This sets the camera default to adjust settings in sets of three so that a short (dark) underexposure, a normal exposure and a long (bright) overexposure can all be taken simultaneously with three presses of a button. Exposure bracketing can be useful for shooting in general when you aren't sure what setting you should use and want to try a range of exposures. In the context of shooting for HDR however it is also extremely important to make sure that the images are not shifted. It is possible to adjust for slightly shifted images but it is highly reccomended that a sturdy tripod be used and all three images snapped in succession to avoid shaking the camera or disturbing the image in some other way. Here are three images which were taken using exposure bracketing. The camera was set to use an exposure compensation change of 2 so it snapped an image at -2, 0 and +2.
None of these images is exceptional or correct, however we will see what happens when we merge them together. The dark image is far too dark but brings out the shape of the trees and the subtler tones of the sky gradient. The bright exposure the colors on the tractor and background trees are more vivid but the sky is totally washed out. The normal image is a nice medium between the two if perhaps a bit on the dark side and a little flat and grey. There are many tools that exist to help you merge the images. For the example I used a GIMP Script-Fu tool called Exposure Blend which creates an exposure blended composite image. Here is the image that was formed after blending the exposures.
You can immediately tell the difference. While the image still seems washed out and very flat there are many places where textures and tones have come through the shadowy areas of the bright exposures and lighter areas have been corrected from the darker exposure. After creating the above image by merging the exposures I then took it a step further by adjusting the color levels of the output image and here is what I got!
This image combines all the corrected exposure values plus regained some of the warmth of the beautiful morning light I was shooting in. This picture captures the feel of the light and the moment in a way none of the original exposures do. Here are a few more examples. Click to enlarge.
Learn to use the Exposure Blend Script-fu Tool in GIMP |
