1. Paper-4 Interactive Translucent Volume Rendering and Procedural Modeling Joe Kniss Simon Premoze Charles HansenDavid Ebert Univ of Utah

2. Introduction • Interactive shading model which captures volumetric light attenuation effects to produce volumetric shadows and the qualitative appearance of translucency. • A technique for volume displacement or perturbation that allows realistic interactive modeling of high frequency detail for real and synthetic volumetric data. • Appearance of many common objects dominated by sub surface scattering effects • Need not be accurate but interactive

3. Volume shading model • Multiple scattering and indirect illumination effects are important and no restrictions on external illumination and optical properties • Color bleeding and diffusion of light across boundaries are also consequences of multiple scattering • Full global illumination , backward scattering and volumetric light sources not part of this model

4. Model • Translucency implies blurring of light thro the medium • Multiple scattering modeled as random walk->light is diffused within volume • Surface shading parameter set automatically using gradient magnitude at the sample

5. Implementation • Tf , light direction and volume data not static. • Diffuse reflectance material , absorption/emission , shadows , indirect attenuation term • Transport color- the color indirect light becomes after getting attenuated by the material

6. Rendering • Uses half angle slicing • modification of the slicing axis allows us to render each slice from the point of view of both the observer and the light. • Total of 3 image buffers • Two buffers are maintained for the attenuation of light in the light direction (current and next), • One buffer for the accumulation of light for the observer, which is typically the frame buffer • Ping-pong blending current next.

7. Volume perturbation

8. Results