Showing papers by "Wolfgang Heidrich published in 2006"

Tomographic reconstruction of transparent objects

Abstract: The scanning of 3D geometry has become a popular way of capturing the shape of real-world objects. Transparent objects, however, pose problems for traditional scanning methods. We present a visible light tomographic reconstruction method for recovering the shape of transparent objects, such as glass. Our setup is relatively simple to implement, and accounts for refraction, which can be a significant problem in visible light tomography.

Symmetric Photography: Exploiting Data-sparseness in Reflectance Fields

Abstract: We present a novel technique called symmetric photography to capture real world reflectance fields. The technique models the 8D reflectance field as a transport matrix between the 4D incident light field and the 4D exitant light field. It is a challenging task to acquire this transport matrix due to its large size. Fortunately, the transport matrix is symmetric and often data-sparse. Symmetry enables us to measure the light transport from two sides simultaneously, from the illumination directions and the view directions. Data-sparseness refers to the fact that sub-blocks of the matrix can be well approximated using low-rank representations. We introduce the use of hierarchical tensors as the underlying data structure to capture this data-sparseness, specifically through local rank-1 factorizations of the transport matrix. Besides providing an efficient representation for storage, it enables fast acquisition of the approximated transport matrix and fast rendering of images from the captured matrix. Our prototype acquisition system consists of an array of mirrors and a pair of coaxial projector and camera. We demonstrate the effectiveness of our system with scenes rendered from reflectance fields that were captured by our system. In these renderings we can change the viewpoint as well as relight using arbitrary incident light fields.

Volume-Surface Trees

Abstract: Many algorithms in computer graphics improve their efficiency by using Hierarchical Space Subdivision Schemes (HS3), such as octrees, kD-trees or BSP trees. Such HS3 usually provide an axis-aligned subdivision of the 3D space embedding a scene or an object. However, the purely volume-based behavior of these schemes often leads to strongly imbalanced surface clustering. In this article, we introduce the VS-Tree, an alternative HS3 providing efficient and accurate surface-based hierarchical clustering via a combination of a global 3D decomposition at coarse subdivision levels, and a local 2D decomposition at fine levels near the surface. First, we show how to efficiently construct VS-Trees over meshes and point-based surfaces, and analyze the improvement it offers for cluster-based surface simplification methods. Then we propose a new surface reconstruction algorithm based on the volume-surface classification of the VS-Tree. This new algorithm is faster than state-of-the-art reconstruction methods and provides a final semi-regular mesh comparable to the output of remeshing algorithms.

Automatic Multiperspective Images

Abstract: Multiperspective images generated from a collection of photographs or a videostream can be used to effectively summarize long, roughly planar scenes such as city streets. The final image will span a larger field of view than any single input image. However, common projections used to make these images, including cross-slits and pushbroom projections, may suffer from depth-related distortions in non-planar scenes. In this paper, we use an aspect-ratio distortion metric to compare these images to standard perspective projections. By minimizing this error metric we can automatically define the picture surface and viewpoints of a multiperspective image that reduces distortion artifacts. This optimization requires only a coarse estimate of scene geometry which can be provided as a depth map or a 2D spatial importance map defining interesting parts of the scene. These maps can be automatically constructed in most cases, allowing rapid generation of images of very long scenes.

25.3: Observations of Luminance, Contrast and Amplitude Resolution of Displays

Abstract: contrast ratio and amplitude resolution are rapidly growing display specifications. Through a series of human factor studies we have developed simple guidelines for these specifications including viewer preference for luminance, optimal contrast ratio and amplitude resolution under realistic conditions. 1. Introduction past, conventional displays have been largely limited to a dynamic range similar to paper under office lighting conditions - approximately two or three orders of magnitude starting at a grayish black and finishing in the hundreds of cd/m 2 . This paradigm of hundreds-to-one contrast ratio, limited luminance and an amplitude resolution in the hundreds of steps is shifting today. Novel display technologies are emerging with the potential of much higher contrast and brightness. Moreover, even existing display technology is being pushed to the limit with a strong increase in display performance. This trend proceeds unevenly with contrast ratio rising faster than luminance, and amplitude resolution remaining largely static. As a result, many display designs make sub-optimal use of the device capabilities. This paper presents a series of human factor studies that aim to provide a basic framework of luminance, contrast ratio and amplitude resolution and their interaction. The use of a High Dynamic Range (HDR) display (1) as the imaging tool for the study, allows a large enough range for each variable to encompass all current and most near-future display technologies. The results of the study can be used to make design decisions for future displays as well as more realistic comparisons of existing devices. 2. Background Video Electronics Standards Association (VESA) and International Organization for Standardization (ISO) provide common guidelines for display specification including luminance and contrast ratio. Peak luminance is generally easy to measure and reported relatively accurately by the industry. Contrast ratio is significantly more challenging. A proper contrast ratio

Sequential sampling for dynamic environment map illumination

Abstract: Sampling complex illumination in the form of environment maps has received a lot of attention in computer graphics. Recent work in this area has demonstrated that drawing samples from the product of light and BRDF produces superior results to other sampling strategies. However, existing methods in this area consider only individual frames, and do not take advantage of coherence in animations. In this paper, we introduce a sequential sampling approach for dynamic environment map illumination. Our algorithm efficiently samples from the product of illumination and BRDF, while exploiting temporal coherence. We demonstrate significant performance benefits over existing methods.

Correlated visibility sampling for direct illumination

Abstract: State-of-the-art importance sampling strategies for direct illumination take into account the importance of the incident illumination, as well as the surface BRDF. Hence, these techniques achieve low variance in unoccluded regions. However, the resulting images still have noise in partially occluded regions as these techniques do not take visibility into account during the sampling process.We introduce the notion of correlated visibility sampling, which considers visibility in partially occluded regions during the sampling process, thereby improving the quality of the shadowed regions. We aim to draw samples in the partially occluded regions according to the triple product of the incident illumination, BRDF and visibility using Monte Carlo sampling followed by Metropolis sampling.

Sequential sampling for dynamic environment maps

Abstract: Sampling of complex direct illumination in the form of high dynamic range (HDR) environment maps has recieved a lot of attention in computer graphics, with major applications in realistic relighting. The best known techniques for direct illumination sample from the product of the incident illumination and the surface reflectance [ Burke et al. 2005 ]. Recent work on sampling from HDR video sequences only take the dynamic importance of the illumination into account while proposing samples for the video sequence. This can be sub-optimal in the presence of high frequencies in both the illumination as well as the surface BRDFs. In this work, we aim to efficiently sample from the product distribution of the illumination and the BRDF in a video sequence with dynamic illumination using asequential Monte Carlo (SMC) sampling strategy. The basic idea is to generate samples according to the product distribution in the first frame of the sequence, and thereafter to filter these samples (particles) in the subsequent frames according to the dynamic product distribution. This sequential sampling mechanism is more efficient than independently sampling from the product distribution at each time step (Figure 1), especially for scenes with high frequencies in both the dynamic illumination and the BRDF. We employ bidirectional importance sampling for generating samples in the first frame of the sequence.

It's tea time!

Abstract: It's Tea Time! How often do we hear this sentence! People from all walks of life sit together to enjoy a cup of tea for the relaxing sense of community and the aesthetic experience that accompanies it. This work of art presents a radically different view of Tea Time and presents an opportunity to experience a contrast between the simulated design presented by the steam and the tactile, physical, "hands on" design seen in the embroidered artistic teapot. The steam seen coming out of the spout of the teapot, is displayed through a high-dynamic range display which makes the viewer feel as if the steam is, in fact, on the front side of the embroidery instead of behind it. The hand-embroidered teapot is created with six colors that are harmonically blended together to form smooth transitions between light and shadow. The varying orientation of the individual stiches make it appear three-dimensional and solid. The red and orange colors symbolize warmth, love, and passion. This piece of art contrasts two very different processes: the ancient craft of embroidery and cutting-edge technology. Both processes are designed to be compelling when experienced together so as to remind us that we live in a world where artistry from any source can be juxtaposed to create more expressive visual communication.

Tomographic reconstruction of transparent objects

Abstract: The scanning of 3D geometry has become a popular way of capturing the shape of real-world objects. Transparent objects, however, pose problems for traditional scanning methods. We present a visible light tomographic reconstruction method for recovering the shape of transparent objects, such as glass. Our setup is relatively simple to implement, and accounts for refraction, which can be a significant problem in visible light tomography.