Rendering three-dimensional (3D) volumes from scan data acquired by computed tomography (CT). A transfer function is applied to a 3D grid of voxels generated from the scan data, each voxel having an associated intensity value, to determine a density value associated with each voxel. A 3D grid of super voxels is generated, each super voxel being formed from a number of adjacent voxels of the 3D grid of voxels, each super voxel having an associated density value. An optimization is performed using the 3D grid of super voxels, based at least in part on a defined super voxel size. A 3D volume is drawn based at least in part on the 3D grid of super voxels and the determined density associated with each super voxel. The super voxel size may be determined based at least in part on a 3D fractal dimension of a 3D volume being rendered.