Ahmed Ghali

Classroom collaboration in the design of tangible interfaces for storytelling

We describe the design of tangible interfaces to the KidPad collaborative drawing tool. Our aims are to support the re-enactment of stories to audiences, and integration within real classroom environments. A six-month iterative design process, working with children and teachers in school, has produced the “magic carpet”, an interface that uses pressure mats and video-tracked and barcoded physical props to navigate a story in KidPad. Reflecting on this process, we propose four guidelines for the design of tangible interfaces for the classroom. (1) Use physical size and shysical props to encourage collaboration. (2) Be aware of how different interfaces emphasize different actions. (3) Be aware that superficial changes to the design can produce very different physical interactions. (4) Focus on open low-tech technologies rather than (over) polished products.

Expected, sensed, and desired: A framework for designing sensing-based interaction

Movements of interfaces can be analyzed in terms of whether they are expected, sensed, and desired. Expected movements are those that users naturally perform; sensed are those that can be measured by a computer; and desired movements are those that are required by a given application. We show how a systematic comparison of expected, sensed, and desired movements, especially with regard to how they do not precisely overlap, can reveal potential problems with an interface and also inspire new features. We describe how this approach has been applied to the design of three interfaces: pointing flashlights at walls and posters in order to play sounds; the Augurscope II, a mobile augmented reality interface for outdoors; and the Drift Table, an item of furniture that uses load sensing to control the display of aerial photographs. We propose that this approach can help to build a bridge between the analytic and inspirational approaches to design and can help designers meet the challenges raised by a diversification of sensing technologies and interface forms, increased mobility, and an emerging focus on technologies for everyday life.

Object and event recognition for stroke rehabilitation

Stroke is a major cause of disability and health care expenditure around the world. Existing stroke rehabilitation methods can be effective but are costly and need to be improved. Even modest improvements in the effectiveness of rehabilitation techniques could produce large benefits in terms of quality of life. The work reported here is part of an ongoing effort to integrate virtual reality and machine vision technologies to produce innovative stroke rehabilitation methods. We describe a combined object recognition and event detection system that provides real time feedback to stroke patients performing everyday kitchen tasks necessary for independent living, e.g. making a cup of coffee. The image plane position of each object, including the patient’s hand, is monitored using histogram-based recognition methods. The relative positions of hand and objects are then reported to a task monitor that compares the patient’s actions against a model of the target task. A prototype system has been constructed and is currently undergoing technical and clinical evaluation.

Vision-mediated interaction with the Nottingham caves

The English city of Nottingham is widely known for its rich history and compelling folklore. A key attraction is the extensive system of caves to be found beneath Nottingham Castle. Regular guided tours are made of the Nottingham caves, during which castle staff tell stories and explain historical events to small groups of visitors while pointing out relevant cave locations and features. The work reported here is part of a project aimed at enhancing the experience of cave visitors, and providing flexible storytelling tools to their guides, by developing machine vision systems capable of identifying specific actions of guides and/or visitors and triggering audio and/or video presentations as a result. Attention is currently focused on triggering audio material by directing the beam of a standard domestic flashlight towards features of interest on the cave wall. Cameras attached to the walls or roof provide image sequences within which torch light and cave features are detected and their relative positions estimated. When a target feature is illuminated the corresponding audio response is generated. We describe the architecture of the system, its implementation within the caves and the results of initial evaluations carried out with castle guides and members of the public.

Image structural information assessment

Many image information assessment techniques have been proposed in the past. Most of them are based on the image histogram. When the histogram of an image is derived, the structural component of the image is generally ignored. The information assessed using the histogram is thus independent of the image spatial attributes. In this investigation an original computational technique for the assessment of the structural information content of an image is described. The developed technique produces as output an information measure which is proportional to the image geometrical attributes such as the size, the shape complexity, etc. The technique is normalised and tested on a series of artificial images. The results obtained are analysed to show how the normalised information is related to the image geometrical attributes. The results obtained are also confirmed when English character images are considered. Finally, conclusions will be drawn in terms of the suitability of the technique for applications in computer imaging problems.

Pattern recognition based on information theory principles

One of the main problems faced in the development of pattern recognition algorithms is assessment of their performance. This paper describes the development of a novel technique for the assessment of information content of 2-D patterns encountered in practical pattern recognition problems. The technique is demonstrated by its application to multi-font typed character recognition. In this work we first developed an information model applicable to any pattern, and its elaboration to measure recognition performance, and second we used this model to derive parameters such as the resolution required to distinguish between the patterns. This has resulted in a powerful method for assessing the performance of any pattern recognition system.

Boundary extraction and polarimetry in translucent specimens for photoelastic stress analysis

We address the problem of providing input to a novel method of interpreting photoelastic data for performing experimental stress analysis of models of engineering components. This method employs conventional photoelastic data relating to the directions of the principal stresses in the specimen (isoclinic data), along with the difference in principal stresses (isochromatic data). Both are used within an inverse boundary element model to reconstruct the load conditions at the model boundary and hence to recover the principal stresses in the specimen without recourse to numerical integration of shear stress gradient. We describe methods of obtaining unwrapped isoclinic and isochromatic phase maps from sequences of images captured within a computer-controlled polariscope. A boundary element model of the specimen, congruent with the isoclinic and isochromatic phase maps, is obtained from an image captured within the polariscope under either traditional lighting conditions or by configuring the polariscope to provide a light field background. Image segmentation reveals the boundary of the specimen, which is then described in terms of simple geometric primitives. Boundary points and geometric descriptions are both used to produce the final boundary element model. The techniques described have been applied to a number of contact specimens; results are presented and discussed.

A Unified Approach to Digital Photoelasticity Incorporating Image Filtering and Inverse Methods

A unified, hybrid experimental/numerical approach to digital photoelasticity has been developed. The system consists of an automated polariscope with image capture facilities together with a suite of dedicated software for setting up and controlling the polariscope, for extracting and unwrapping the isoclinic and isochromatic data, for constructing a boundary element (BE) model congruent with the edges of the specimen on the photoelastic images, and for obtaining separated stresses and boundary conditions such as contact stresses via an inverse BE technique. In this paper, the integration of the various techniques is described and illustrated using typical results.

Information-based shape description with scale, translation and rotation invariance

This paper proposes a technique based on information theory principles for shape description of 2-D images. By its essence the technique is invariant to rotation and translation. We first describe how the translational information content of an image may be defined, identified, assessed and analysed. The effect of the size is then assessed and quantified which permits us to propose a modified definition of translational information content invariant to scale. In order to demonstrate the feasibility of the developed techniques, a series of tests were carried out on rectangular and triangular shapes. The results illustrate the power of the translational information assessment techniques in analysing and describing 2-D images. The use of these techniques in shape description is also introduced.

Rotational information in shape description

Using information theory, this investigation propose a novel technique for shape description which is invariant to translation, rotation and in most cases also to scale. This new numeric shape descriptor is based on the measure of rotational information content of an image. In this paper we first review some popular metric shape description features. These features are then used to analyze the feasibility of using the rotational information for shape description, and by means of a comparative study we show how the rotational information is related to well known metric shape descriptors such as area, circularity and elongation. Finally, the results obtained are discussed and analyzed, and conclusions drawn in terms of the suitability of the technique for shape description in image recognition problems.