Depth-peeling for texture-based volume rendering

We present the concept of volumetric depth-peeling. The proposed method is conceived to render interior and exterior iso-surfaces for a fixed iso-value and to blend them without the need to render the volume multiple times. The main advantage of our method over pre-integrated volume rendering is the ability to extract arbitrarily many iso-layers for the given iso-value. Up to now, pre-integrated volume rendering is only capable of visualizing the nearest two (front and back-faced) iso-surfaces. A further gain of our algorithm is the rendering speed, since it does not depend on the number of layers to be extracted, as for previous depth-peeling methods. We rather exploit the natural slicing order of 3D texturing to circumvent the handicap of storing intermediate layers in textures, as done in polygonal-based depth-peeling approaches. We are further capable of rapidly previewing the volume data, when only few context information about the concerning dataset is available. An important example of use in the area of non-photorealistic rendering is given, where we can distinguish between visible and hidden silhouettes, which are important elements in stylization. By using standard OpenGL extensions, we allow the exploration of spatial relationships in the volume -at interactive rates- in hardware.