High Dynamic Range Images
Written on December 29, 2012
In photography, dynamic range is the difference between the lighest and the darkest parts of an image. High dynamic range (HDR) images have been manipulated to a greater range of shades of colour from light to dark.
HDR images are an attempt to show a level of detail that we can see with our eyes. When we look at a scene “in person” the lens in our eyes will constantly adjust focus, and the iris(aperture) will constantly adjust according to the lighting conditions.
In the same way that what we "see" has already been "processed" in several ways including correcting for white balance and filling in the "blind spot". Whether it is due to the light sensitive cells in our eyes or due to how our brains process the information, we see the world with higher dynamic range than a camera can capture.
Creating high dynamic range images
The first step is to take several pictures of the same scene; each of these should correctly expose different parts of the scene. If your camera has an "exposure bracketing" function, then this is the easiest way to take the pictures. Exposure bracketing will set your camera to take several pictures, one at the specified exposure and then two more at a lighter and darker exposure.
To get the best results in your HDR images you should use a tripod and a shutter release cable.
There are many different programs that you can use, I have used a free program called "Luminance HDR" to create these examples; this program is available for Windows, Mac, and Linux.
In each of the images some parts of the image are correctly exposed and other parts are not. The detail in the sky increases in the images to the right, whereas the details in the forest and field are lost.
After loading the images, the program will read the exposure settings from the images’ ISO information.
The program will also align the images, since even in the best of conditions the images will be slightly offset.
The pictures can be processed using a number of different processes. Each of these uses different mathematical algorithms to blend the images, so choose the method that gives the best result for your set of images.
So, once the image has been processed, we arrive at the following HDR image. You will notice that there is visible detail in both the dark and the light areas.
by Simon James Allanach, edited by Alan Frost