Dental model repair is a critical stage in the orthodontic treatment. The repaired teeth need to preserve the original morphological features, and the algorithm is required to be automatic for saving time and avoiding uncertainty caused by human handling. This paper presents an efficient and automatic algorithm to repair the tooth models' large holes. Our algorithm consists of three main steps: model's principal axis determination, model's contours processing (generation and repair), and hole surface reconstruction and fairing. We propose a novel LRBC (Linear Regression on Boundaries' Centers) algorithm to determine the model's principal axis. After generating contours based on the principal axis, we adopt point-normal cubic B-spline curve interpolation to repair each broken contour line. At last, we reconstruct holes' point-sets by constrained Delaunay triangulation, and smooth the patches with a modified Laplacian operator. Experiments on different dental models demonstrate that our algorithm can not only achieve a result with a high morphological similarity and a low error, but also satisfy the requirements of actual orthodontic applications.
In this paper we illustrate an application that displays high-resolution images on Multi-Projector Tiled High Resolution Display Wall. Our goal is to enable the users to view high-resolution image data, such as photos from satellites and microscopes. Panoramas can also be played circularly. Users pan across the image, scale the image, and play panoramas interactively.
Our prototype is implemented over a local area network with a PC cluster and a monitor. Image data are initially stored in the monitor PC. The critical issues emphasized in this paper are: using dynamically-selected multi-resolution texture hierarchy to overcome the limit of texture size, using binary-tree transferring structure to reduce the latency from O(N) to O(log2 N)(N is the number of Displayer PCs), and using parallel Macro-Micro clocks for system synchronization to eliminate accumulated displacement while achieving a high frame-rate.
Recent developments in computer graphics hardware and distributed parallel rendering research have greatly improved the rendering capabilities of graphics workstations and PC clusters. However, the display resolution of monitors is still far from being enough, and thus become the bottleneck of visualization. Recently, more and more people are focusing on using multiple projectors to form a large display wall and provide high display resolutions. One essential problem of these kinds of systems is how to calibrate the projectors and make the whole display wall seamless and perfect. Traditional software calibration algorithms have three main problems: re-rendering and over illumination in overlapping regions, calibration being not general. In this paper, we introduce our multi-projector tiled display wall calibration system using a digital camera which mainly focuses on solving these three problems. For the first two, we make specific divisions to the overlapping regions basing on our dividing algorithms and each projector project only part of the overlapping images. Furthermore, we make some sub-division to each part and make the mosaic seamless. And for the last problem, we adopt the idea of the open source software VNC, and implement our calibration on the layer of Windows desktop, thus make the calibration process application independent.
In this paper, we discussed the possibility of introducing chaotic sequences into digital watermarking systems as potential substitutes to commonly used m-sequences. Chaotic sequences have several good properties including the availability of a great number of them, the ease of their generation, as well as their sensitive dependence on their initial conditions. And the quantization does not destroy the good properties. We focus our discussion on the discrete-time dynamical systems operating in chaotic state including Chebyshev maps and logistic maps. Both real valued and binary chaotic sequences are studied and experimented with a digital watermarking system similar to the well-known NEC system. Chaotic sequences are used to modulate information bits into white noise-like wideband watermark signals to be added into the cover objects. The robustness against common signal processing and lossy compression and robust test tools like Stirmark of these systems are tested and compared. Preliminary results are satisfactory. However, in this paper, we only test chaotic sequences scheme with digital images. Tests with other media including video and audio signals will be done at next step. And the good properties of chaos will be further explored, both theoretically and experimentally.
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