Fast perspective volume rendering with splatting by utilizing a ray-driven approach

Volume ray casting is based on sampling the data along sight rays. In this technique, reconstruction is achieved by a convolution, which collects the contribution of multiple voxels to one sample point. Splatting, on the other hand, is based on projecting data points on to the screen, and reconstruction is implemented by an "inverted convolution", where the contribution of one data element is distributed to many sample points (i.e. pixels). Splatting produces images of a quality comparable to ray casting but at greater speeds. This is achieved by pre-computing the projection footprint that the interpolation kernel leaves on the image plane. However, while fast incremental schemes can be utilized for orthographic projection, the perspective projection complicates the mapping of the footprints and is therefore rather slow. In this paper, we merge the technique of splatting with the principles of ray casting to yield a ray-driven splatting approach. We imagine splats as being suspended in object space, a splat at every voxel. Rays are then spawned to traverse the space and intersect the splats. An efficient and accurate way of intersecting and addressing the splats is described. Not only is ray-driven splatting inherently insensitive to the complexity of the perspective viewing transform, it also offers acceleration methods such as early ray termination and bounding volumes, which are methods that traditional voxel-driven splatting cannot benefit from. This results in competitive or superior performance for parallel projection, and superior performance for perspective projection.