No description available.

No description available.

This paper explores the surface properties of skin and eyes and their importance in the acceptance and success of a digital human face, specifically in relation to the uncanny valley. The uncanny valley hypothesis states that as a human representation approaches photo-realism, subtle differences from reality become unsettling. Recent studies suggest that the uncanny valley could exist over a far greater range, affecting abstract human representations as well. These competing findings are explored by analyzing how changes to the surface of a digital character affect its level of acceptance. A female facial model is used as a base to compare a spectrum of different simulated real-world materials. The variations range from materials that are nearly identical to human skin, to those that are completely divergent from it, thus unnatural. After studying this catalogue of materials, it is concluded that given the right conditions, the uncanny valley can occur when facial representations are very near realism, as well as when human-likeness is quite distant from reality.

No description available.

No description available.

No description available.

Presence has various definitions, but can be understood as the sensation that a virtual environment is a real place, that the user is actually in the virtual environment rather than at the display terminal, or that the medium used to display the environment has disappeared leaving only the environment itself. We present an attempt to unite various presence approaches by reducing each to what we believe is a common basis – the psychology of behaviour selection and control – and re-conceptualizing presence in these terms by defining cognitive presence – the mental state where the VE rather than the real environment is acting as the basis for behaviour selection. The bulk of this work represents the construction of a three-layer connectionist model to explain and predict this concept of cognitive presence. This model takes input from two major sources: the perceptual modalities of the user (bottom-up processes), and the mental state of the user (top-down processes). These two basic sources of input competitively spread activation to a central layer which competitively determines which behaviour script will be applied to regulate behaviour. We demonstrate the ability of the model to cope with current notions of presence by using it to successfully predict two published findings: one (Hendrix & Barfield, 1995) showing that presence increases with an increase in the geometric field of view of the graphical display, and another (Sallnas, 1999), which demonstrates the positive relationship between presence and the stimulation of more than one sensory modality. Apart from this theoretical analysis, we also perform two experiments to test the central tenets of our model. The first experiment aimed to show that presence is affected by both perceptual inputs (bottom-up processes), conceptual inputs (top-down processes), and the interaction of these. We collected 103 observations from a 2x2 factorial design with stimulus quality (2 levels) and conceptual priming (2 levels) as independent variables, and as dependent variable we used three measures of presence (Slater, Usoh & Steed’s scale (1995), Witmer & Singer’s (1998) Presence Questionnaire and our own cognitive presence measure) for the dependent variable. We found a significant main effect for stimulus quality and a significant interaction, which created a striking effect: priming the subject with material related in theme to the content of the VE increased the mean presence score for those viewing the high quality display, but decreased the mean of those viewing the low quality display. For those not primed with material related to the VE, no mean presence difference was discernible between those using high and low quality displays. The results from this study suggest that both top-down and bottom-up activation should be taken into account when explaining the causality of presence. Our second study aimed to show that presence comes about as a result not of raw sensory information, but rather due to partly-processed perceptual information. To do this we created a simple three group comparative design, with 78 observations. Each one of the three groups viewed the same VE under three display conditions: high-quality graphical, low-quality graphical, and text-only. Using the model, we predicted that the text and low-quality graphics displays would produce the same presence levels, while the high-quality display would outperform them both. The results were mixed, with the Slater, Usoh & Steed scale showing the predicted pattern, but the Presence Questionnaire showing each condition producing a significantly different presence score (in the increasing order: text, low-quality graphics, high-quality graphics). We conclude from our studies that the model shows the correct basic structure, but that it requires some refinement with regards to its dealings with non-immersive displays. We examined the performance our presence measure, which was found to not perform satisfactorily. We conclude by proposing some points relevant to the methodology of presence research, and by suggesting some avenues for future expansion of our model.

The 3D shape and position of objects inside the human body are commonly detected using Computed Tomography (CT) scanning. CT is an expensive diagnostic option in economically disadvantaged areas and the radiation dose experienced by the patient is significant. In this dissertation, we present a technique for reconstructing the 3D shape and position of bullets from multiple X-rays. This technique makes us of ubiquitous X-ray equipment and a small number of X-rays to reduce the radiation dose. Our work relies on Image Segmentation and Volume Reconstruction techniques. We present a method for segmenting bullets out of X-rays, based on their signature in intensity profiles. This signature takes the form of a distinct plateau which we model with a number of parameters. This model is used to identify horizontal and vertical line segments within an X-Ray corresponding to a bullet signature. Regions containing confluences of these line segments are selected as bullet candidates. The actual bullet is thresholded out of the region based on a range of intensities occupied by the intensity profiles that contributed to the region. A simple Volume Reconstruction algorithm is implemented that back-projects the silhouettes of bullets obtained from our segmentation technique. This algorithm operates on a 3D voxel volume represented as an octree. The reconstruction is reduced to the 2D case by reconstructing a slice of the voxel volume at a time. We achieve good results for our segmentation algorithm. When compared with a manual segmentation, our algorithm matches 90% of the bullet pixels in nine of the twelve test X-rays. Our reconstruction algorithm produces an acceptable results: It achieves a 70% match for a test case where we compare a simulated bullet with a reconstructed bullet.

A single chip line-rasterizer that overcomes the major bottleneck in graphics display systems has been designed by the author on a 4408 element gate array marketed by Plessey Semiconductors limited. The rasterizer was fabricated by Plessey using their 2 micron, double-level metal ISO CMOS process, in the United Kingdom. Two identifiable bottlenecks in the redraw speed on a general graphics display system are video memory bandwidth and rasterization speed (in dots produced per second). The rasterizer described here is capable of working in parallel with other rasterizers to overcome the rasterization bottleneck. Systems incorporating it are flexible and expandable. The rasterizer requests a primitive from a host or master part of the system. Once it has a primitive to work on, it begins rasterization. The rasterizer queues requests to write dots to the video memory part of the system. The device accepts two ordered pairs of 16-bit numbers as start-of-line and end-of-line coordinates, on an 8-bit bus; the dot addresses are in the form of two 16-bit numbers on a 32-bit bus. Simulation with CLASSIC showed that the device could be clocked at up to 8 MHz and would then produce dots at between 2 MHz and 4 MHz (dependent on the type of line) after the initial analysis overheads. This means that any video memory bandwidth may be fully used with this device and any improvements in memory bandwidth may be taken advantage of in a system using the parallel rasterization scheme. The Plessey test engineers exercised the device to prove the success of the fabrication. Further tests were performed by the author. In these, the rasterizer was seen to gather data correctly. The rasterization of a range of different types of lines, manhattan and general, short and long and lines of different direction, was tested. The various algorithm terminations were verified and all branches exercised. The flow control on the pixel bus was checked. The device used for all the tests, performed correctly at 10 MHz (design specification 8 MHz) which corresponds to a maximum rasterization speed of 5 MHz for 0° and 90° lines and between 2.5 MHz and 3.3 MHz for general lines. The results show that the rasterizer performance will allow full use of the memory bandwidth of the system and hence overcome the major bottleneck in many graphics display systems. / Thesis (M.Sc.)-University of Natal, 1987.

No description available.