Jochen Lang

DISCO: acquisition of translucent objects

Translucent objects are characterized by diffuse light scattering beneath the objects surface. Light enters and leaves an object at possibly distinct surface locations. This paper presents the first method to acquire this transport behavior for arbitrary inhomogeneous objects. Individual surface points are illuminated in our DISCO measurement facility and the objects impulse response is recorded with a high-dynamic range video camera. The acquired data is resampled into a hierarchical model of the objects light scattering properties. Missing values are consistently interpolated resulting in measurement-based, complete and accurate representations of real translucent objects which can be rendered with various algorithms.

Interactive rendering of translucent objects

This paper presents a rendering method for translucent objects, in which view point and illumination can be modified at interactive rates. In a preprocessing step the impulse response to incoming light impinging at each surface point is computed and stored in two different ways: The local effect on close-by surface points is modeled as a per-texel filter kernel that is applied to a texture map representing the incident illumination. The global response (i.e. light shining through the object) is stored as vertex-to-vertex throughput factors for the triangle mesh of the object. During rendering, the illumination map for the object is computed according to the current lighting situation and then filtered by the precomputed kernels. The illumination map is also used to derive the incident illumination on the vertices which is distributed via the vertex-to-vertex throughput factors to the other vertices. The final image is obtained by combining the local and global response. We demonstrate the performance of our method for several models.

Interactive Rendering of Translucent Objects

This paper presents a rendering method for translucent objects, in which viewpoint and illumination can be modified at interactive rates. In a preprocessing step, the impulse response to incoming light impinging at each surface point is computed and stored in two different ways: The local effect on close‐by surface points is modeled as a per‐texel filter kernel that is applied to a texture map representing the incident illumination. The global response (i.e. light shining through the object) is stored as vertex‐to‐vertex throughput factors for the triangle mesh of the object. During rendering, the illumination map for the object is computed according to the current lighting situation and then filtered by the precomputed kernels. The illumination map is also used to derive the incident illumination on the vertices which is distributed via the vertex‐to‐vertex throughput factors to the other vertices. The final image is obtained by combining the local and global response. We demonstrate the performance of our method for several models.

Planned Sampling of Spatially Varying BRDFs

Measuring reflection properties of a 3D object involves capturing images for numerous viewing and lightingdirections. We present a method to select advantageous measurement directions based on analyzing the estimationof the bi‐directional reflectance distribution function (BRDF). The selected directions minimize the uncertaintyin the estimated parameters of the BRDF. As a result, few measurements suffice to produce models that describethe reflectance behavior well. Moreover, the uncertainty measure can be computed fast on modern graphics cardsby exploiting their capability to render into a floating‐point frame buffer. This forms the basis of an acquisitionplanner capable of guiding experts and non‐experts alike through the BRDF acquisition process. We demonstratethat spatially varying reflection properties can be captured more efficiently for real‐world applications using ouracquisition planner.

Local compliance estimation via positive semidefinite constrained least squares

We present a method to estimate a positive semidefinite matrix by linear least squares, and we apply this method to the estimation of local compliance matrices during deformable object modeling. Estimation of physical quantities from measurements has to consider noise due to measurement and modeling inaccuracy. Enforcing constraints during estimation can guarantee physically plausible results even under difficult measurement conditions.

View planning for BRDF acquisition

The estimation of the bi-directional reflectance distribution function (BRDF) of a 3D object requires reflectance measurements under numerous viewing and lighting directions. This sketch summarizes our method to select advantageous directions. Uncertainty minimization of the estimated BRDF parameters forms the theoretical underpinning of our acquisition planner. Our hardware-accelerated planner can aid manual and automatic measurement, reduces measurement effort and increases the quality of the acquired models.

Virtualizing real-world objects

High quality, virtual 3D models are quickly emerging as a new multimedia data type with applications in such diverse areas as e-commerce, online encyclopedias, or virtual museums, to name just a few. We present new algorithms and techniques for the acquisition and real-time interaction with complex textured 3D objects and show how these results can be seamlessly integrated with previous work into a single framework for the acquisition, processing, and interactive display of high quality 3D models. In addition to pure geometry, such algorithms also have to take into account the texture of an object (which is crucial for a realistic appearance) and its reflectance behavior. The measurement of accurate material properties is an important step towards photorealistic rendering, where both the general surface properties as well as the spatially varying effects of the object are needed. Recent work on the image-based reconstruction of spatially varying BRDFs enables the generation of high quality models of real objects from a sparse set of input data. Efficient use of the capabilities of advanced PC graphics hardware allows for interactive rendering under arbitrary viewing and lighting conditions and realistically reproduces the appearance of the original object.

Modeling the world: the virtualization pipeline

High quality, virtual 3D models are quickly emerging as a new multimedia data type with applications in such diverse areas as e-commerce, online encyclopaedias, or virtual museums, to name just a few. The paper presents new algorithms and techniques for the acquisition and real-time interaction with complex textured 3D objects and shows how these results can be seamlessly integrated with previous work into a single framework for the acquisition, processing, and interactive display of high quality 3D models. In addition to pure geometry, such algorithms also have to take into account the texture of an object (which is crucial for a realistic appearance) and its reflectance behavior. The measurement of accurate material properties is an important step towards photorealistic rendering, where both the general surface properties as well as the spatially varying effects of the object are needed. Recent work on the image-based reconstruction of spatially varying BRDFs (bidirectional reflectance distribution function) enables the generation of high quality models of real objects from a sparse set of input data. Efficient use of the capabilities of advanced PC graphics hardware allows for interactive rendering under arbitrary viewing and lighting conditions and realistically reproduces the appearance of the original object.