High Dynamic Range

High dynamic range (HDR) photography is a new technique for combining several similar images with the objective of extending the final dynamic range, or range of brightness recorded in a image. The dynamic range of film and digital sensors is such that under high-contrast conditions it may be impossible to record satisfactorily all the detail in both the lightest and darkest regions. Films and sensors may simply be incapable of coping. Set the exposure for the bright areas and the detail will be lost in the darkest regions. Set it for the dark areas and the highlights will burn out. Even a compromise exposure may prove inadequate.

One solution is to take a number of identically framed images at different exposures, and then combine the best areas of each into a final HDR image. The camera should be set up on a tripod and great care must be taken to ensure that it is not moved as controls are reset. A series of identical images is then recorded so as to record effectively all the detail over the entire dynamic range presented by the scene. A typical sequence might incorporate four images exposed at two-stop intervals.

The four images can then be combined by masking the various combined lays to reveal all the most appropriately exposed areas in a single final image. Unfortunately, this process can be complex, so it may prove difficult to produce a satisfactory seamless result. Specialist software, such as Photomatix Pro, is now available to carry out such processing in an almost automatic manner.