Lee Iverson

Logical/linear operators for image curves

We propose a language for designing image measurement operators suitable for early vision. We refer to them as logical/linear (L/L) operators, since they unify aspects of linear operator theory and Boolean logic. A family of these operators appropriate for measuring the low-order differential structure of image curves is developed. These L/L operators are derived by decomposing a linear model into logical components to ensure that certain structural preconditions for the existence of an image curve are upheld. Tangential conditions guarantee continuity, while normal conditions select and categorize contrast profiles. The resulting operators allow for coarse measurement of curvilinear differential structure (orientation and curvature) while successfully segregating edge-and line-like features. By thus reducing the incidence of false-positive responses, these operators are a substantial improvement over (thresholded) linear operators which attempt to resolve the same class of features. >

Two stages of curve detection suggest two styles of visual computation

The problem of detecting curves in visual images arises in both computer vision and biological visual systems. Our approach integrates constraints from these two sources and suggests that there are two different stages to curve detection, the first resulting in a local description, and the second in a global one. Each stage involves a different style of computation: in the first stage, hypotheses are represented explicitly and coarsely in a fixed, preconfigured architecture; in the second stage, hypotheses are represented implicitly and more finely in a dynamically constructed architecture. We also show how these stages could be related to physiology, specifying the earlier parts in a relatively fine-grained fashion and the later ones more coarsely.

Ziplock Snakes

We propose a snake-based approach that allows a user to specify only the distant end points of the curve he wishes to delineate without having to supply an almost complete polygonal approximation. This greatly simplifies the initialization process and yields excellent convergence properties. This is achieved by using the image information around the end points to provide boundary conditions and by introducing an optimization schedule that allows a snake to take image information into account first only near its extremities and then, progressively, toward its center. In effect, the snakes are clamped onto the image contour in a manner reminiscent of a ziplock being closed.These snakes can be used to alleviate the often repetitive task practitioners face when segmenting images by eliminating the need to sketch a feature of interest in its entirety, that is, to perform a painstaking, almost complete, manual segmentation.

The Organization Of Curve Detection: Coarse Tangent Fields And Fine Spline Coverings

We propose a new paradigm for curve detection in which an autonomous and atomic description is computed between measurements on the image and global curves. The description takes the form of a discrete tangent field, i.e.. an estimated representation of quantized tangents and curvatures at each possible trace point. We then present a new algorithm for inferring global curves through this tangent field. by inferring a covering of the global curve. The elements of the covering are short splines, each of which moves according to a potential distribution computed from the tangent field. Both stages of the algorithm are parallel and both bear some analogy to biological mechanisms for curve detection

Towards understanding IT security professionals and their tools

We report preliminary results of our ongoing field study of IT professionals who are involved in security management. We interviewed a dozen practitioners from five organizations to understand their workplace and tools. We analyzed the interviews using a variation of Grounded Theory and predesigned themes. Our results suggest that the job of IT security management is distributed across multiple employees, often affiliated with different organizational units or groups within a unit and responsible for different aspects of it. The workplace of our participants can be characterized by their responsibilities, goals, tasks, and skills. Three skills stand out as significant in the IT security management workplace: inferential analysis, pattern recognition, and bricolage.

TerraVision II: visualizing massive terrain databases in VRML

To disseminate 3D maps and spatial data over the Web, we designed massive terrain data sets accessible through either a VRML browser or the customized TerraVision II browser. Although not required to view the content, TerraVision II lets the user perform specialized browser level optimizations that offer increased efficiency and seamless interaction with the terrain data. We designed our framework to simplify terrain data maintenance and to let users dynamically select particular sets of geo-referenced data. Our implementation uses Java scripting to extend VRMLs base functionality and the External Authoring Interface to offer application-specific management of the virtual geographic environment.

Constraint-Based Tiled Windows

Typical computer workstations employ window managers for creating, destroying, and arranging windows on the screen. Window managers generally follow either a desktop metaphor, allowing windows to overlap each other like sheets of paper on a desk, or they use a tiling model, arranging each window with a specific size and location that avoids overlap. Desktop models allow for the most layout freedom, but can be frustrating to use when dealing with a large number of windows that must all be visible at once. Tiling models guarantee that each window will be completely visible on the screen, but thus far have provided relatively poor mechanisms for controlling layout decisions. This article describes work in tiled window management featuring a constraint-based layout mechanism. With it the user can specify the appearance of individual windows and constrain relationships between windows, thus exercising necessary control over the tiling process. We discuss our constraint model and then detail an implementation approach that would make use of those constraints.

Intentional access management: making access control usable for end-users

The usability of access control mechanisms in modern distributed systems has been widely criticized but little studied. In this paper, we carefully examine one such widely deployed access control mechanism, the one embedded in the WebDAV standard, from the point-of-view of an end-user trying to decide how to grant or deny access to some resource to a third party. This analysis points to problems with the conceptual usability of the system. Significant effort is required on the part of the user to determine how to implement the desired access rules; the user, however, has low interest and expertise in this task, given that such access management actions are almost always secondary to the collaborative task at hand. The analysis does however indicate a possible solution: to recast the access control puzzle as a decision support problem in which user intentions (i.e. the descriptions of desired system outputs) are interpreted by an access mediator that either automatically or semi-automatically decides how to achieve the designated goals and provides enough feedback to the user. We call such systems intentional access management (IAM) systems and describe them in both specific and general terms. To demonstrate the feasibility and usability of the proposed IAM models, we develop an intentional access management prototype for WebDAV. The results of a user study conducted on the system show its superior usability compared to traditional access management tools like the access control list editor.

Under the hood of GeoVRML 1.0

GeoVRML 1.0 provides geoscientists with a rich suite of enabling capabilities that cannot be found elsewhere. That is, the ability to model dynamic 3-D geographic data that can be distributed over the web and interactively visualized using a standard browser configuration. GeoVRML includes nodes for VRML97 that perform this task; addressing issues such as coordinate systems, scalability, animation, accuracy, and preservation of the original geographic data. The implementation is released as open source and includes various tools for generating GeoVRML data. All these facilities provide geoscientists with an excellent medium to present complex 3-D geographic data in a dynamic, interactive, and web-accessible format. We illustrate these capabilities using real-world examples drawn from diverse application areas.

Going with the flow: email awareness and task management

Email use in the context of everyday work practices, or email flow, has not been heavily studied. We present the results of a pair of studies examining how users interlace email with their day-to-day, ongoing work processes. We demonstrate that our subjects use email as a tool for managing moment-to-moment attention and task focus. We also provide a model of this workflow that builds upon an existing model by Venolia et al. Finally, we provide specific design recommendations to enhance the usability of email clients in support of these modes of interaction.