Allison W. Klein

Building and using a scalable display wall system

Princetons scalable display wall project explores building and using a large-format display with commodity components. The prototype system has been operational since March 1998. Our goal is to construct a collaborative space that fully exploits a large-format display system with immersive sound and natural user interfaces. Our prototype system is built with low-cost commodity components: a cluster of PCs, PC graphics accelerators, consumer video and sound equipment, and portable presentation projectors. This approach has the advantages of low cost and of tracking technology well, as high-volume commodity components typically have better price-performance ratios and improve at faster rates than special-purpose hardware. We report our early experiences in building and using the display wall system. In particular, we describe our approach to research challenges in several specific research areas, including seamless tiling, parallel rendering, parallel data visualization, parallel MPEG decoding, layered multiresolution video input, multichannel immersive sound, user interfaces, application tools, and content creation.

Non-photorealistic virtual environments

We describe a system for non-photorealistic rendering (NPR) of virtual environments. In real time, it synthesizes imagery of architectural interiors using stroke-based textures. We address the four main challenges of such a system — interactivity, visual detail, controlled stroke size, and frame-to-frame coherence — through image based rendering (IBR) methods. In a preprocessing stage, we capture photos of a real or synthetic environment, map the photos to a coarse model of the environment, and run a series of NPR filters to generate textures. At runtime, the system re-renders the NPR textures over the geometry of the coarse model, and it adds dark lines that emphasize creases and silhouettes. We provide a method for constructing non-photorealistic textures from photographs that largely avoids seams in the resulting imagery. We also offer a new construction, art-maps, to control stroke size across the images. Finally, we show a working system that provides an immersive experience rendered in a variety of NPR styles.

Unconstrained isosurface extraction on arbitrary octrees

This paper presents a novel algorithm for generating a watertight level-set from an octree. We show that the levelset can be efficiently extracted regardless of the topology of the octree or the values assigned to the vertices. The key idea behind our approach is the definition of a set of binary edge-trees derived from the octrees topology. We show that the edge-trees can be used define the positions of the isovalue-crossings in a consistent fashion and to resolve inconsistencies that may arise when a single edge has multiple isovalue-crossings. Using the edge-trees, we show that a provably watertight mesh can be extracted from the octree without necessitating the refinement of nodes or modification of their values.

Video mosaics

We present a method for creating a video mosaic, a two-dimensional arrangement of small source videos (tiles) that suggests a larger, unified target video. We develop a distance measure to assess the match between source and target based on average color and also three-dimensional wavelet decomposition signatures in the YIQ color space. We also introduce a dynamic programming algorithm that automatically chooses the smaller tiling sub-sequences from a large collection of candidate source video sequences to best match the target video. After the selection process, the color in the tiling videos is automatically adjusted to better suggest the target video. Finally, our method also supports the use of different tiling shapes to create an additional level of visual interest.