The main purpose of this paper is to discuss the global illumination methods in the context of real-time walkthrough. Our work focuses on an accurate illumination of complex scenes; the intensity of the lights can also be interactively modified. This feature is particularly relevant within the context of a production pipeline: After the 3D modeling, photorealistic walkthrough is often used to detect inappropriate reflections or to measure illumination rates. The known methods that usually work in real-time do not simulate all light paths for large scenes. However, some methods provide a full global illumination with a computation time close to a few seconds. This paper shows how this calculation time can be reduced to approach real-time animation thanks to a specific method derived from the photon mapping.