High-Quality Unstructured Volume Rendering

For the visualization of volume data the application of transfer functions is used widely. In this area the preintegration technique allows high quality visualizations and the application of arbitrary transfer functions. For regular grids, this approach leads to a two-dimensional pre-integration table which easily fits into texture memory. In contrast to this, unstructured meshes require a three-dimensional pre-integration table. As a consequence, the available texture memory limits the resolution of the pre-integration table and the maximum local derivative of the transfer function. Discontinuity artifacts arise if the resolution of the pre-integration table is too low. This paper presents a novel approach for accurate rendering of unstructured grids using the multi-texturing capabilities of commodity PC graphics hardware. Our approach achieves high quality by reconstructing the colors and opacities of the pre-integration table using the high internal precision of the pixel shader. Since we are using standard 2D multi-texturing we are not limited in the size of the pre-integration table. By combining this approach with a hardware-accelerated calculation of the pre-integration table, we achieve both high quality visualizations and interactive classification updates.