Accelerating virtual endoscopy

Applying volumetric ray tracing in interactive visualization has always been limited by low rendering speeds. This paper presents methods for accelerating first-hit ray tracing based virtual endoscopy with negligible impact on image quality, which aim at improving empty-space traversal (tracing all rays to the colon wall and storing the results in a depth buffer) and shading (surface normal approximation at hit locations and simple Phong shading applied to obtain pixel color). The first method proposed accelerates empty-space traversal by exploiting inter-ray coherence based on the fact that the colon wall is a (C2) continuous natural surface, which does not exhibit erratic behavior, such as sharp jumps, steps or edges. The second method presented improves shading performance by using conditional interpolation in pixel space. Results have been successfully implemented in the virtual colonoscopy application ColVis, maintained by the author