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How to Create Awesome HDR Photographs
Jayesh Limaye, Jun 24, 2010 1244 hrs ISTA step by step guide to make HDR images
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Most of you may be now familiar with HDR or High Dynamic Range in games. HDR enabled games look amazingly lifelike with better lighting and shadows and the clouds look ultra-realistic. What actually makes HDR images different from traditional images is the fact that they have a higher range of intensity levels (this article is meant for a layman and we are therefore not using technically correct words like Radiance and Luminance), and it is more like the way we perceive through our eyes.
Digital cameras are cheap these days, and you get image quality that rivals that of SLRs of yesteryear. But if you observe closely, there is still a lack of realism in the images that are obtained by these digicams. The problem is that the CCD is simply unable to capture the complete range of intensity of light in an image at one shot. An example of this is that the shadows are not dark enough, highlights are not bright enough or at times are too bright, and then there is the loss of perception of color of the light source. This is where HDR photography comes into play.
In HDR photography it is possible to capture and display the complete range of intensity of light and color that makes the photographs look lifelike with a richer contrast that doesn't look artificial (usually). Contrary to popular perception, HDR photography does not require an expensive digicam. Even entry-level cameras, which allow you to set different exposure levels or shutter speeds, can do a good job. All you need to do is take photographs of a scene with different exposure settings. If your camera supports Exposure Bracketing, then select the Continuous Shooting mode with the camera set to Aperture Priority and select an exposure increment of +/-2. The camera will automatically vary the shutter speed each time the shutter button is pressed and vary the exposure. The larger the number of photographs and the larger the exposure difference, the better will be the results you get.
The most common technique for HDR photography is to shoot a number of photographs of a scene using different exposure settings. Thus, some photographs are underexposed, while some are overexposed. The underexposed photographs capture the details in the lighter and reflective areas better, while the overexposed photographs capture details in the darker areas. These images are now combined into a single image, taking the better things from each image, thus resulting in an image that contains a larger range of light intensity. This method is known as Exposure Blending and there are several programs available that can do it.
Since HDR images contain a huge amount of data and it is not possible to display it as it should actually appear on conventional CRTs and LCD monitors, a method known as Tone Mapping is employed. Tone Mapping attempts to compress the entire dynamic range of light intensity into a viable range that can be displayed on the above display devices. This produces an image that retains realistic color and contrast.
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