The key to interactive but software-based volume rendering is an efficient approach to skip parts of the volume which do not contribute to the visualization results due to the visualization mapping in use and current parameter settings. In this work, an efficient way of skipping non-contributing parts of the data is presented. Skipping is done at a negligible effort by extracting just potentially contributing voxels from the volume during a preprocessing step, and by storing them in a derived enumeration-like data structure. Within this structure, voxels are ordered in a way which is optimized for the chosen compositing technique, and which allows to efficiently skip further voxels as they become irrelevant for the result due to changes to the visualization parameters. Together with a fast shear/warp-based rendering and flexible shading based on look-up tables, this approach can be used to provide interactive rendering of segmented volumes, featuring object-aware clipping, transfer functions, shading models, and compositing modes defined on a per-object basis, even on standard desktop hardware. In combination with a space-efficient encoding of the enumerated voxel data, the approach is well-suited for visualization over low-bandwidth networks, like the Internet.