Volumetric three-dimensional (3-D) displays allow the user to explore a 3-D scene free of joysticks, keyboards, goggles, or trackers. For non-trivial scenes, computing and transferring a 3-D image to the display takes hundreds of seconds, which is a serious bottleneck for many applications. We propose to represent the 3-D scene with an occlusion camera reference image (OCRI). The OCRI is a compact scene representation that stores only and all scene samples that are visible from a viewing volume centered at a reference viewpoint. The OCRI enables computing and transferring the 3-D image an order of magnitude faster than when the entire scene is processed. The OCRI approach can be readily applied to several volumetric display technologies; we have tested the OCRI approach with good results on a volumetric display that creates a 3-D image by projecting 2-D scene slices onto a rotating screen