Virtual Ray Sampling for Direct Volume Rendering using Hermite Interpolation

Keywords

Direct volume rendering, reconstruction filtering, virtual sampling.

Abstract

Virtual sampling has been proposed as an alternative of pre-integration to reduce artifacts caused by an insufficient sampling of the ray profiles in volume-rendering applications. According to the originally recommended implementation, a 3D tricubic B-spline reconstruction is applied to evaluate true samples along the rays, while between the true samples, virtual samples are calculated by using a 1D Catmull-Rom spline interpolation. The virtual samples can be evaluated much faster, but they can still well approximate the true samples. Therefore, the rendering performance can be drastically improved at the cost of a very slight quality degradation. Nevertheless, in this paper, we show that the original virtual sampling scheme does not exploit the fact, that the applied tricubic B-spline reconstruction filter together with its analytic derivative filters provide Hermite samples. Therefore, it is more natural to use Hermite interpolation along the rays rather than Catmull-Rom spline interpolation. From a sampling-theoretical point of view, this modification requires half of the true samples to guarantee the same reconstruction quality. Furthermore, concerning the evaluation of the true samples, we also investigate a recently published GPU-accelerated triquadratic B-spline filtering as an alternative of the tricubic B-spline filtering.