Abstract: A voxel transfer circuit that implements high-speed voxel transfer operations. When implemented in a 2D or 3D texture mapping circuit of a graphics system, or in a graphics card adapter of a workstation, the voxel transfer circuit provides a comprehensive, accelerated volume rendering capability to the existing imaging pipeline. For each voxel in a volume data set, the voxel transfer circuit generates a texel having an opacity value and a color value based on one or more properties of the voxel including the local gradient magnitude and a lighting model. The relationship between these values is referred to herein as a classification or transfer function. In the present invention, the voxel transfer circuit implements a transfer function that employs a gradient-influenced classification. Such a transfer function generates opacity and color values of structures with excellent edge and surface discrimination.

Abstract: A volumetric pre-clipping method that guarantees only a minimal number of sample points along rays that pass through a volume data set will need to be processed by a volume rendering system. Pre-clipping is a two step process. First, a projection of the volume is made onto an image plane based on the orthographic or perspective view desired. Each bounding vertex of the volume data set is multiplied by the appropriate transformation matrix to transform the vertices from source space to view space. The transformed vertices establish on the view space image plane the projection outline of the volume data set. By definition, only rays cast from pixels on the image plane within this projection outline will pass through the volume data set. Pixels outside the projection outline do not need to be considered. Rays and pixels in view space are transformed back to source space by multiplication with the appropriate inverse transformation matrix for an orthographic or perspective view.

Abstract: A ray transform method for performing 3D spacial volume transformation for perspective view rendering of a volume data set on a 2D graphics display. A backward mapping approach is used whereby each destination point along a ray is transformed and resampled from the source. The rays converge at the center of projection, or the eye pont, from the projection plane for the perspective view desired. Each ray has a unique ray transform matrix which is combined with an orthographic model view matrix to yield a combined inverse matrix. The floating point values of the combined inverse matrix are coded into a 32 bit fixed point format having 16 bits of scalar and 16 bits of fraction. Once this coding has been done, then transforming consecutive points along a destination ray becomes simple integer adds. The method supports two resampling techniques, nearest neighbor and trilinear interpolation.