HDR: An Introduction to High Dynamic Range Photography

Image Capture Bracketing Methods

Image capture for HDR imaging is slightly different than traditional single-shot low dynamic range photography. The goal is not necessarily to capture a single frame that best represents the scene before the camera, but to capture a series of different exposures that are intended to best capture the various tonalities contained within the scene.

In simpler terms: HDR imaging begins with a bracketed series of low dynamic range images that run the gamut from underexposure to overexposure. Perhaps counterintuitively, the underexposed source images from the series are used for the extreme highlight details, and the overexposed source images provide the shadow detail.

It makes perfect sense when you think about it for a moment. In the underexposed images, all but the spotlights, sun disk, or other extremely bright image elements will be thrown to shadows, but the highlight areas will have a degree of detail. In the overexposed images, all but the darkest shadows will be blown out and white-clipped. But those very dark shadows and low tones will appear close to normally exposed—providing shadow detail that would be lost in a normally exposed tonal range. By combining these extremely exposed source images, along with like images from the series that are exposed for the middle tonal areas, the tonal information gleaned from all photos provides the HDR generation program with enough information throughout the image curve to create an HDR output image that shows ...