A method to approximate image surfaces using irregular samples is proposed. Experimental results show that a high compression ratio can be achieved for simple or complicated images. A method accounting for the three-dimensional effects is proposed as a way of selecting the irregular samples from the image. Approximation spline knots are chosen along the contours, and the knot replacement is sensitive to the curvature along contours and the density of contours in the near neighborhood. In general, the proposed method was shown to reduce the reconstruction error both qualitatively and quantitatively, and can be used to model the image surface for the purpose of data compression and representation. This approach retains key features in images and throws away redundant data.>

Three algorithms for coding the boundary of two-dimensional shapes are described. In each algorithm, each boundary point is coded with respect to another point picked at random from the boundary. Using this method, an effective and efficient correlation technique to match two-dimensional shapes is developed. This technique can be used to match shapes of arbitrary scale and orientation. The given shape can have a closed or open boundary or even have a portion obstructed from the view. Matching can be performed with varying degrees of detail, giving the technique an added robustness, against geometrical distortions. It can also discriminate between different shapes. On an IBM 3033 computer it typically takes 10 CPU-seconds to generate one correlation curve between two shapes, each with a 500-point boundary curve.>

Locking is a simple scheme to synchronize multiple updates in a multicopy distributed database system. Various schemes were proposed before to maintain the consistency of the distributed database. But these schemes were compared to each other mostly on heuristic base. In this paper, three analytic queueing models for the Network Semaphore scheme, Hopping Permit scheme, and Adaptive Hopping Permit scheme are developed. Incorporating special waiting stages allows the latter two control schemes to he modeled as M/G/1 queueing systems. Shown in this paper are various performance measures of the models, which can provide much insight into these schemes. The validity of these models is verified by the simulation results.

In clinic practice, a series of transaxial views are usually obtained from a patient in the CAT scanner system. There are interests to present this data at different oblique views. Experience of implementing the generation programs shows the necessity to minimize its processing time in an on line environment. An orthogonal view generation program seems to be the best. This program allows user to specify an orthogonal cut in the displayed view interactively. The processing time for the specified cut is less than four minutes. A second subsequent cut can be drawn in the first generated cut. This orthogonal view generation program permits curvelinear cuts in the displayed view. This curvelinear cut provides a very untradirional dis play in radiology. It is useful in displaying a slice-sectional view of the spinal column of patients. Neuradiologists are interested in using this capability to study the dimension of the spinal column. In this paper, the orthogonal view generation program will be described in detail. The features of this display program will be compared with a number of other alternative programs.