Abstract: Methods, systems, and computer program products for processing three-dimensional image data to render an image from a viewpoint within or beyond an occluding region of the image data are disclosed. According to one method, a set of three-dimensional image data is accessed. The image data includes image data for a surface of interest and image data for a region occluding the surface of interest from a desired viewpoint. The viewpoint may be within or beyond the occluding region. A plurality of rays is cast from the viewpoint to the surface. Along each ray, an occlusion determination is made independent from a volume rendering transfer function definition to render voxels within the occluding region as transparent or partially transparent. The volume rendering transfer function is applied along a portion of each ray outside of the occluding region to render voxels defining surface of interest as visible. The voxels that define the surface are displayed as visible.