Neubauer, A.Forster, M.Wegenkittl, R.Mroz, L.Bühler, K.Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe2014-01-302014-01-3020043-905673-07-X1727-5296https://doi.org/10.2312/VisSym/VisSym04/301-310Many applications of virtual endoscopy require the display of background objects behind the semi-transparent surface of the investigated organ. This paper deals with pre-processing and visualization of background objects for virtual endoscopy. A new first-hit ray casting technique for efficient perspective iso-surfacing of arbitrarily selected objects of interest is described: Visualization is performed without the use of dedicated hardware or data structures limiting flexibility (e.g., polygonal meshes or distance fields). The speedup is gained by exploiting inter-pixel coherency and by finding a near-optimal compromise between reduction of ray-tracking distances and limitation of the administrational cost associated with this reduction. The algorithm was developed by enhancing the previously published cell-based first-hit ray casting algorithm. This paper describes the original algorithm and explains the extensions needed to achieve interactive rendering of background objects.