A technique which uses a high dynamic range image as a light source during rendering.
By capturing a high dynamic range image (or series of such images to represent an environment map) of a real scene, it is possible to illuminate rendered objects using that data, so that the rendered objects will match the lighting conditions of the original scene exactly. This produces an extremely realistic looking image, as there will be no discrepancies between the lighting conditions in the real and computer-generated portions of the final image.