Overall Objectives
Scientific Foundations
Application Domains
New Results
Contracts and Grants with Industry
Other Grants and Activities

Section: New Results

3D Data Rendering and Visualization

Light Warping for Enhanced Surface Depiction

Participants : Romain Vergne, Romain Pacanowski, Pascal Barla, Xavier Granier, Christophe Schlick.

Recent research on the human visual system shows that our perception of object shape relies in part on compression and stretching of the reflected lighting environment onto its surface. We use this property to enhance the shape depiction of 3D objects by locally warping the environment lighting around main surface features [20] . Contrary to previous work, which require specific illumination, material characteristics and/or stylization choices, our approach en- hances surface shape without impairing the desired appearance. Thanks to our novel local shape descriptor, salient surface features are explicitly extracted in a view-dependent fashion at var- ious scales without the need of any pre-process. We demonstrate our system on a variety of rendering settings, using object materials ranging from diffuse to glossy, to mirror or refractive, with direct or global illumination, and providing styles that range from photorealistic to non-photorealistic. The warping itself is very fast to compute on modern graphics hardware, enabling real-time performance in direct illumination scenarios.

Figure 10. Our novel light warping approach enhances surface depiction by locally compressing patterns of reflected lighting. Such a process preserves the overall appearance of 3D objects. Observe how various surface features are properly enhanced in both settings: sharp features on the face, broad variations around shoulders, and rough details on the torso.

Real-time Soft Shadow Rendering

Participants : Gaël Guennebaud, Vincent Forest, Loïc Barthe, Mathias Paulin, Baoguang Yang, Jieqing Feng, Xinguo Liu.

Shadows is a fundamental visual effect which both increase the level of realism of a 3D scene, and help to identify spatial relationships between objects. This latter observation makes them particularly important in the context of interactive 3D applications. Generating high quality soft shadows in real-time is still an open challenge. In collaboration with University of Toulouse, we extended state of the art object based methods to deal with alpha textured models [21] which are often used to efficiently represents complex geometries such as foliage and or fences. In contrast to object based methods, the Soft Shadow Mapping algorithm is usually significantly faster excepted for large penumbrae. In collaboration with the State Key Lab of CAD&CG of Zhejiang University (China) we addressed this limitation by exploiting the screen space and light space coherence via a packet-based and a hierarchical traversal schemes [22] . These optimizations allowed us to reach an acceleration up to a factor ten without trading off the quality (Figure 11 ).

Figure 11. Two images rendered in real time using our optimized soft shadow mapping algorithm.

Vector-based lighting

Participants : Romain Pacanowski, Xavier Granier, Christophe Schlick.

We extend to caching [12] , [15] , [35] the use of our volumetric representation that captures low-frequency indirect illumination, structure intended for efficient storage and manipulation of illumination on graphics hardware. It is based on a 3D texture that stores a fixed set of irradiance vectors. This texture is built during a preprocessing step by using almost any existing global illumination software. Then during the rendering step, the indirect illumination within a voxel is interpolated from its associated irradiance vectors, and is used by the fragment shader as additional local light sources. The technique can thus be considered as following the same trend as ambient occlusion or precomputed radiance transfer techniques, as it tries to include visual effects from global illumination into real-time rendering engines. But its 3D vector-based representation offers additional robustness against local variations of geometric of a scene. We demonstrate that our technique may also be employed as an efficient and high quality caching data structure for bidirectional rendering techniques.

Figure 12. Virtual Museum of 3D Objects for Computer Graphics


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