Kok-Lim Low

Model simplification using vertex-clustering

This paper presents a practical technique to automaticallycompute approximations of polygonal representations of3D objects. It is based on a previously developed modelsimplification technique which applies vertex-clustering.Major advantages of the vertex-clustering technique are itslow computational cost and high data reduction rate, andthus suitable for use in interactive applications. This paperadvances the technique with careful consideration ofapproximation quality and smoothness in transitionsbetween different levels of simplification, whilemaintaining its efficiency and efb%iveness. Its majorcontributions include: accuracy in grading vertices forindication of their visual importance, robustness inclustering for better preservation of important fimtures andconsistencies between levels of simplification, thick-lineswith dynamic normals to maximize visual fidelity, andexploitation of object and image space relationship forlevels-of-simplificationdetermination.

Saliency-enhanced image aesthetics class prediction

We present a saliency-enhanced method for the classification of professional photos and snapshots. First, we extract the salient regions from an image by utilizing a visual saliency model. We assume that the salient regions contain the photo subject. Then, in addition to a set of discriminative global image features, we extract a set of salient features that characterize the subject and depict the subject-background relationship. Our high-level perceptual approach produces a promising 5-fold cross-validation (5-CV) classification accuracy of 78.8%, significantly higher than existing approaches that concentrate mainly on global features.

Life-sized projector-based dioramas

We introduce an idea and some preliminary results for a new projector-based approach to re-creating real and imagined sites. Our goal is to achieve re-creations that are both visually and spatially realistic, providing a small number of relatively unencumbered users with a strong sense of immersion as they jointly walkaround the virtual site.Rather than using head-mounted or general-purpose projector-based displays, our idea builds on previous projector-based work on spatially-augmented realityand shader lamps. Using simple white building blocks we construct a static physical model that approximates the size, shape, and spatial arrangementof the site. We then project dynamic imagery onto the blocks, transforming the lifeless physical model into a visually faithful reproduction of the actual site. Some advantages of this approach include wide field-of-view imagery, real walking around the site, reduced sensitivity to tracking errors, reduced sensitivity to system latency, auto-stereoscopic vision, the natural addition of augmented virtualityand the provision of haptics.In addition to describing the major challenges to (and limitations of) this vision, in this paper we describe some short-term solutions and practical methods, and we present some proof-of-concept results.

Interacting with spatially augmented reality

We present the notion of projector-based spatially augmented reality (SAR), and explore how it can be used as an effective user interface to enable users to easily and naturally interact with their real physical environment and the virtual environment. In SAR, the users physical environment is illuminated with images projected from the projectors. We then describe a framework that can easily incorporate different types of interactions on a continuum of display surfaces and input devices. More specifically, in the framework, we first establish an understanding of the 3D relationship between the user, the projectors and the display surfaces. Then, with the help of some new calibration and rendering techniques, only a simple procedure is needed to effectively illuminate the display surfaces. We describe various underlying techniques and discuss the results in the context of three different applications.

SandCanvas: a multi-touch art medium inspired by sand animation

Sand animation is a performance art technique in which an artist tells stories by creating animated images with sand. Inspired by this medium, we have developed a new multi-touch digital artistic medium named SandCanvas that simplifies the creation of sand animations. SandCanvas also goes beyond traditional sand animation with tools for mixing sand animation with video and replicating recorded free-form hand gestures. In this paper, we analyze common sand animation hand gestures, present SandCanvass intuitive UI, and describe implementation challenges we encountered. We also present an evaluation with professional and novice artists that shows the importance and unique affordances of this new medium.

Efficient Constraint Evaluation Algorithms for Hierarchical Next-Best-View Planning

We recently proposed a new and efficient next-best- view algorithm for 3D reconstruction of indoor scenes using active range sensing. We overcome the computation difficulty of evaluating the view metric function by using an adaptive hierarchical approach to exploit the various spatial coherences inherent in the acquisition constraints and quality requirements. The impressive speedups have allowed our NBV algorithm to become the first to be able to exhaustively evaluate a large set of 3D views with respect to a large set of surfaces, and to include many practical acquisition constraints and quality requirements. The success of the algorithm is greatly dependent on the implementation efficiency of the constraint and quality evaluations. In this paper, we describe the algorithmic details of the hierarchical view evaluation, and present efficient algorithms that evaluate sensing constraints and surface sampling densities between a view volume and a surface patch instead of simply between a single view point and a surface point. The presentation here provides examples for the design of efficient algorithms for new sensing constraints.

Immersive electronic books for surgical training

Immersive electronic books (IEBooks) for surgical training will let surgeons explore previous surgical procedures in 3D. The authors describe the techniques and tools for creating a preliminary IEBook, embodying some of the basic concepts.

Automatic image alignment for 3D environment modeling

We describe an approach for automatically registering color images with 3D laser scanned models. We use the chi-square statistic to compare color images to polygonal models texture mapped with acquired laser reflectance values. In complicated scenes we find that the chi-square test is not robust enough to permit an automatic global registration approach. Therefore, we introduce two techniques for obtaining initial pose estimates that correspond to a coarse alignment of the data. The first method is based on rigidly attaching a camera to a laser scanner and the second utilizes object tracking to decouple these imaging devices. The pose estimates serve as an initial guess for our optimization method, which maximizes the chi-square statistic over a local space of transformations in order to automatically determine the proper alignment.

Combining head-mounted and projector-based displays for surgical training

We introduce and present preliminary results for a hybrid display system combining head-mounted and projector-based displays. Our work is motivated by a surgical training application where it is necessary to simultaneously provide both a highfidelity view of a central close-up task (the surgery) and visual awareness of objects and events in the surrounding environment. In this article, we motivate the use of a hybrid display system, discuss previous work, describe a prototype along with methods for geometric calibration, and present results from a controlled human subject experiment. This article is an invited resubmission of work presented at IEEE Virtual Reality 2003. The article has been updated and expanded to include (among other things) additional related work and more details about the calibration process.

Computing bounding volume hierarchies using model simplification

This paper presents a framework that uses the outputs of model simplification to guide the construction of bounding volume hierarchies for use in, for example, collision detection. Simplified models, besides their application to multiresolution rendering, can provide clues to the object’s shape. These clues help in the partitioning of the object’s model into components that may be more tightly bounded by simple bounding volumes. The framework naturally employs both the bottom-up and the topdown approaches of hierarchy building, and thus can have the advantages of both approaches. Experimental results show that our method built on top of the framework can indeed improve the bounding volume hierarchy, and as a result, significantly speedup the collision detection.