This chapter discusses how precomputed data can be reused in rendering by applying precomputed light transport algorithms in pbrt software. Artists modeling scenes generally desire quick feedback, and many applications require not just faster rendering but also full interactivity. It is desirable that the images generated by interactive rendering share in the benefits of the improvements in light transport algorithms of recent years. A variety of precomputed light transport algorithms have been developed to this end. The general idea is to separate the complete rendering computation into a portion that can be performed offline in a preprocess and stored in a data structure, such that the results can then be incorporated into the final rendering computation later. When rendering a walkthrough of a scene (where only the camera position changed from frame to frame, and the objects, materials, and lights stayed the same), the same photon map could be reused across all of the frames of the animation, saving the cost of recomputing it.