Feature-driven ambient occlusion for direct volume rendering

Ambient occlusion techniques were introduced to improve data comprehension by bringing soft fading shadows. They consist in attenuating light by considering the occlusion resulting from the presence of neighboring structures. Recently introduced in volume rendering, we show that the straightforward application of ambient occlusion in direct volume rendering has its limits as rendering a multi-layer volume results in overdarkening the internal layers of the volume. This paper proposes to address the overdarkening issue by computing ambient occlusion according to the features present in the dataset. This allows us to neglect inter-occlusions between features without losing the auto-occlusions that give cues on the shape of the considered features. We use a GPU-based approach with bricking to speed up the computations of our ambient occlusion method. Results show that our approach not only improves the visual quality of images compared to classical ambient occlusion, but it is also less parametersensitive, thus furthermore improving usability for every-day users.