The modern digital camera is an excellent example of imaging technology, but the human eye can still do better. Take dynamic range, which is the difference between the brightest and the dimmest object that can be perceived in a scene. A point-and-shoot camera might achieve 256:1; a top-end digital SLR, 2,000:1; and the human eye, 10,000:1.
This 10,000:1 contrast ratio matches the dynamic range of a high-contrast daylight scene. This means there are still some scenes that we can see perfectly yet, when photographed, display black shadow areas devoid of detail and/or bright white areas.
High-dynamic-range (HDR) photography is a technique designed to overcome this limitation. It permits a scene to be reproduced as it appears to the human eye, but it can also go beyond this to produce some truly dramatic results.
You can create HDR effects with even a fairly ordinary digital camera. The secret is to take several photographs of the same scene at different exposures, typically -2EV (two stops underexposed), 0EV (exposed normally) and +2EV (two stops overexposed). The 0EV shot will show most of the scene correctly, the -2EV image will reveal detail in the highlights, and the +2EV one will record detail in the dark areas. Between them, these photographs contain all the information necessary to produce an HDR image.
The creation of that image is carried out using dedicated HDR software, which combines the images so that the best parts of each are incorporated.
Having created an HDR photograph, we’re faced with the unfortunate fact that neither an LCD monitor nor a print has sufficient dynamic range to reproduce it correctly. The final step, therefore, which uses the technique of exposure fusion, tone compression or detail enhancing (often referred to as tone mapping), processes the image in such a way that it can be viewed on an ordinary monitor or as a print.
Create images with HDR
Step 1. The HDR software we’re using can correct any alignment errors between our three photos, but better results are achieved by eliminating these problems at the outset. Mount your camera on a tripod and stand it on a firm, level surface to prevent it moving while you compose and capture photographs.
Step 2. If there’s enough light, select a low ISO value such as 100. The lower the ISO, the less image noise will result. This is particularly important in HDR photography, since the tone-mapping process has the effect of adding noise. Turn off the flash to prevent your camera compensating for underexposure.