Section: New Results

Editing and Modeling

Tomography-Based Volume Painting

Participant: I. Ihrke

Although volumetric phenomena are important for realistic rendering and can even be a crucial component in the image, the artistic control of the volume’s appearance is challenging. Appropriate tools to edit volume properties are missing, which can make it necessary to use simulation results directly. Alternatively, high-level modifications that are rarely intuitive, e.g., the tweaking of noise function parameters, can be utilized. We have introduced [18] a solution to stylize single-scattering volumetric effects in static volumes. Hereby, an artistic and intuitive control of emission, scattering and extinction becomes possible, while ensuring a smooth and coherent appearance when changing the viewpoint. Our method is based on tomographic reconstruction, which we link to the volumetric rendering equation. It analyzes a number of target views provided by the artist and adapts the volume properties to match the appearance for the given perspectives. Additionally, we describe how we can optimize for the environmental lighting to match a desired scene appearance, while keeping volume properties constant. Finally, both techniques can be combined. We demonstrate several use cases of our approach and illustrate its effectiveness.

Implicit Skinning

Participant: G. Guennebaud

In collaboration with IRIT (Toulouse), we extended our implicit skinning method to a new approach for interactive character skinning called elastic implicit skinning. The method simulates skin contacts between limbs as well as the effect of skin elasticity (Figure 12 ). In addition, we go a step further towards the automation of the rigging process: our method doesn't require the definition of skinning weights. Elastic implicit skinning takes the best features of the recent implicit skinning method, and makes it robust to extreme character movements. While keeping the idea of implicit skinning, namely approximate the character by 3D scalar fields in which mesh-vertices are appropriately re-projected, we depart from the processing pipeline used so far. Implicit skinning is history independent and uses an initial skinning solution (e.g., linear blending or dual quaternions) to correct vertex positions at each frame. Our new approach is history dependent; the mesh directly tracks the iso-surfaces of the scalar field over time. Technically our solutions include: new implicit surface composition operators and a tangential relaxation scheme derived from the as-rigid-as possible energy. This work  [101] has been presented at SIGGRAPH Asia this year.

Multi-scale Editing

Participant: G. Guennebaud

In the continuation of our Growing Least Square approach [5] for the multi-scale analysis of shape, we developed a novel tool that enables the direct editing of surface features in large point-clouds or meshes [19] . This is made possible by a novel multi-scale analysis of unstructured point-clouds that automatically extracts the number of relevant features together with their respective scale all over the surface. Then, combining this ingredient with an adequate multi-scale decomposition allows us to directly enhance or reduce each feature in an independent manner. Our feature extraction is based on the analysis of the scale-variations of locally fitted surface primitives combined with unsupervised learning techniques. Our tool may be applied either globally or locally, and millions of points are handled in real-time. The resulting system enables users to accurately edit complex geometries with minimal interaction.

Manipulation of Anisotropic Highlights

Participants: B. Raymond, P. Barla, G. Guennebaud, X. Granier

We have developed [20] a system for the direct editing of highlights produced by anisotropic BRDFs, which we call anisotropic highlights. We first provide a comprehensive analysis of the link between the direction of anisotropy and the shape of highlight curves for arbitrary object surfaces. The gained insights provide the required ingredients to infer BRDF orientations from a prescribed highlight tangent field. This amounts to a non-linear optimization problem, which is solved at interactive framerates during manipulation. Taking inspiration from sculpting software, we provide tools that give the impression of manipulating highlight curves while actually modifying their tangents. Our solver produces desired highlight shapes for a host of lighting environments and anisotropic BRDFs.