We believe that navigation in information spaces is best supported by tapping into our natural spatial and geographic ways of thinking. To this end, we are developing a new computer interface model called Pad. The ongoing Pad project uses a spatial metaphor for computer interface design. It provides an intuitive base for the support of such applications as electronic marketplaces, information services, and on-line collaboration. Pad is an infinite two-dimensional information plane that is shared among users, much as a network file system is shared. Objects are organized geographically; every object occupies a well defined region on the Pad surface. For navigation, Pad uses "portals" - magnifying glasses that can peer into and roam over different parts of this single infinite shared desktop; links to specific items are established and broken continually as the portal's view changes. Portals can recursively look onto other portals. This paradigm enables the sort of peripheral activity generally found in real phy...

this paper was supported by NSF grant ECS-8206321. A shorter description of this work was published in the Proceedings of SPIE, vol. 432, Applications of Digital Image Processing VI, The International Society for Optical Engineering, Bellingham, Washington. Authors' address: RCA David Sarnoff Research Center, Princeton, NJ 08540. Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. 1983 ACM 0730-0301/83/1000-0217 $00.75 ACM Transactions on Graphics, Vol. 2. No. 4, October 1983, Pages 217-236. 218 . P. J. Burt and E. H. Adelson Fig. 1. A pair of images may be represented as a pair of surfaces above the (x, y) plane. The problem of image splining is to join these surfaces with a smooth seam, with as little distortion of each surface as possible. tiple telescope photographs. In each of these cases, the mosaic technique is used to construct an image with a far larger field of view or level of detail than could be obtained with a single photograph. In advertising or computer graphics, the technique can be used to create synthetic images from possibly unrelated components. A technical problem common to all applications of photomosaics is joining two images so that the edge between them is not visible. Even slight differences in image gray level across an extended boundary can make that boundary quite noticeable. Unfortunately, such gray level differences are frequently unavoidable; they may be due to such factors as differe...

The mapping of images onto surfaces may substantially increase the realism and information content of computer-generated imagery. The projection of a flat source image onto a curved surface may involve sampling difficulties, however, which are compounded as the view of the surface changes. As the projected scale of the surface increases, interpolation between the original samples of the source image is necessary; as the scale is reduced, approximation of multiple samples in the source is required. Thus a constantly changing sampling window of view-dependent shape must traverse the source image. To reduce the computation implied by these requirements, a set of prefiltered source images may be created. This approach can be applied to particular advantage in animation, where a large number of frames using the same source image must be generated. This paper advances a "pyramidal parametric " prefiltering and sampling geometry which minimizes aliasing effects and assures continuity within and between target images. Although the mapping of texture onto surfaces is an excellent example of the process and provided the original motivation for its development, pyramidal parametric data structures admit of wider application. The aliasing of not only surface texture, but also highlights and even the surface representations themselves, may be minimized by pyramidal parametric means.

This paper surveys methods for simplifying and approximating polygonal surfaces. A polygonal surface is a piecewiselinear surface in 3-D defined by a set of polygons

As an advanced form of visibility culling, occlusion culling detects hidden objects and prevents them from being rendered. An occlusion-culling algorithm that can effectively accelerate interactive graphics must simultaneously satisfy the following criteria: # Generality. It should be applicable to arbitrary models, not limited to architectural models or models with many large, polygonal occluders. # Significant Speed-up. It should not only be able to cull away large portions of a model, but do so fast enough to accelerate rendering. # Portability and Ease of Implementation. It should contain as few assumptions as possible on special hardware support. It must also be robust (i.e. insensitive to floating-point errors). Based on proper problem decomposition and efficient representations of cumulative occlusion, this dissertation presents algorithms that sa...

We present a new representation for time-varying image data that allows for varying---and arbitrarily high---spatial and temporal resolutions in different parts of a video sequence. The representation, called multiresolution video, is based on a sparse, hierarchical encoding of the video data. We describe a number of operations for creating, viewing, and editing multiresolution sequences. These operations support a variety of applications: multiresolution playback, including motion-blurred "fast-forward" and "reverse"; constantspeed display; enhanced video scrubbing; and "video clip-art" editing and compositing. The multiresolution representation requires little storage overhead, and the algorithms using the representation are both simple and efficient. CR Categories and Subject Descriptors: H.5.1 [Information Interfaces]: Multimedia Information Systems---video I.3.3 [Computer Graphics]: Picture/Image Generation---display algorithms I.4.10 [Image Processing]: Image Representation---h...

We describe a new approach to the problem of motion planning for mobile robots on natural, nonhomogenous terrain. Our approach computes a multiresolution representation of the terrain using wavelets, and hierarchically plans the path through sections which are well approximated on coarser levels and relatively smooth. Unlike most methods, the hierarchical approximation errors are used explicitly in a cost function to distinguish preferred terrain sections. The error is computed using the corresponding wavelet coefficients. The path planning algorithm uses a new non-scalar path cost measure based on the sorted terrain costs along the path. This measure can be incorporated into standard global path search algorithms and yields intuitively good paths. Additional constraints for specific robots can be integrated into this approach for efficient hierarchical motion planning on rough terrain. We present the algorithms and experimental results for real terrain data.

Abstract-Schema-based representations for visual knowledge are integrated with constraint satisfaction techniques. This integration is discussed in a progression of three sketch map interpretation pro-grams: Mapsee-1, Mapsee-2, and Mapsee-3. The programs are evalu-ated by the criteria of descriptive and procedural adequacy. The eval-uation indicates that a schema-based representation used in combination with a hierarchical arc consistency algorithm constitutes a modular, efficient, and effective approach to the structured represen-tation of visual knowledge. The schemata used in this representation are embedded in composition and specialization hierarchies. Speciali-zation hierarchies are further expanded into discrimination graphs. Index Terms-Constraint satisfaction, discrimination graphs, hier-archical arc consistency, model-based vision, recognition, schema rep-resentations, sketch maps. I.

The characteristic (or intrinsic) scale of a local image pattern is the scale parameter at which the Laplacian provides a local maximum. Nearly every position in an image will exhibit a small number of such characteristic scales. Computing a Gaussian jet at a characteristic scale provides a scale invariant feature vector for tracking, matching, indexing and recognition. However, the computational cost of directly searching the scale axis for the characteristic scale at each image position can be prohibitively expensive.

Abstract. The characteristic (or intrinsic) scale of a local image pattern is the scale parameter at which the Laplacian provides a local maximum. Nearly every position in an image will exhibit a small number of such characteristic scales. Computing a vector of Gaussian derivatives (a Gaussian jet) at a characteristic scale provides a scale invariant feature vector for tracking, matching, indexing and recognition. However, the computational cost of directly searching the scale axis for the characteristic scale at each image position can be prohibitively expensive. We describe a fast method for computing a vector of Gaussian derivatives that are normalised to the characteristic scale at each pixel. This method is based on a scale equivariant half-octave binomial pyramid. The characteristic scale for each pixel is determined by an interpolated maximum in the Difference of Gaussian as a function of scale. We show that interpolation between pixels across scales can be used to provide an accurate estimate of the intrinsic scale at each image point. We present an experimental evaluation that compares the scale invariance of this method to direct computation using FIR filters, and to an implementation using recursive filters. With this method we obtain a scale normalised Gaussian Jet at video rate for a 1/4 size PAL image on a standard 1.5 Ghz Pentium workstation. 1