Jan C. Hardenbergh

The VolumePro real-time ray-casting system

This paper describes VolumePro, the world’s first single-chip realtime volume rendering system for consumer PCs. VolumePro implements ray-casting with parallel slice-by-slice processing. Our discussion of the architecture focuses mainly on the rendering pipeline and the memory organization. VolumePro has hardware for gradient estimation, classification, and per-sample Phong illumination. The system does not perform any pre-processing and makes parameter adjustments and changes to the volume data immediately visible. We describe several advanced features of VolumePro, such as gradient magnitude modulation of opacity and illumination, supersampling, cropping and cut planes. The system renders 500 million interpolated, Phong illuminated, composited samples per second. This is sufficient to render volumes with up to 16 million voxels (e.g., 256) at 30 frames per second. CR Categories: B.4.2 [Hardware]: Input/Output and Data Communications—Input/Output DevicesImage display; C.3 [Computer Systems Organization]: Special-Purpose and ApplicationBased Systems—Real-time and embedded systems; I.3.1 [Computer Graphics]: Hardware Architecture—Graphics processor;

Emissive clipping planes for volume rendering

Figure 1. The inner walls of the colon are easy to see. On the right the colon extends into the volume. While the walls are clear, the clip plane itself makes the image too distracting to be useful. Figure 2. The emissive clip plane reveals muscle (blue), fatty tissue (dull red), the hip bone in the lower left and a fibrous mass in the lower right. The resulting image shows both the clip plane and the colon walls.

fMRI visualization of multiple functional areas

The reconstructed scan data consists of a volume dataset for each activation area as well as the anatomy and vasculature (blood vessels). We display the anatomy and vasculature to provide context for the activations. In hardware that is two texture reads and two dependent (LUT) reads. Naively, each activation volume requires a texture lookup and two dependent reads. Display of three activation areas requires 13 texture reads, 3 serial pixel subtractions and 4 additions. This is not possible on the VP1000 [Wu 2003]. Also, memory requirements, complexity and performance on current graphics processors leads us to look for alternative solutions to displaying multiple activation areas. e-mail: jch@terarecon.com Image rendered the TeraRecon VolumePro 1000. Data courtesy of MGH 3D Imaging Service. Application knowledge: Shirley Miller. Exposition