Differential Photon Mapping - Consistent Augmentation of Photographs with Correction of all Light Paths

Augmenting images with consistent lighting is possible with differential rendering. This composition technique requires two lighting simulations, one simulation with only real geometry and another one with additional virtual objects. The difference of the two simulations can be used to modify the original pixel colors. The main drawback of differential rendering is that not all modified light paths can be displayed: The result of the lighting simulation is visible in a reflective object instead of the real environment, augmented with virtual objects. Moreover, many regions in the photograph remain unchanged and the same work is done twice without any visual effect. In this paper we present a new approach for augmenting a photograph with only a single photon mapping simulation. The changes in lighting introduced by a virtual object are directly simulated using a differential photon map. All light paths intersecting the virtual object are corrected. To demonstrate the correctness of our approach, we compare our simulation results with real photographs.