92 ABSTRACTS OF PAPERS ACCEPTED FOR PUBLICATION

Local window operations are frequently used to filter data in image processing applications. In this paper the implementation of several local operations on an SIMD computing structure is considered. These operations are: local median, local maximum, local mean, and local sorting. Efficient implementa- tion is achieved by factoring the operation such that partial results may contribute to more than one local computation. The cost of these operations in terms of computation, storage, and routing on a mesh connected processor is discussed.

The Representation and Display of Scenes with a Wide Range of Detail. STEVEN M. RUBIN. Bell Laboratories, Holmdel, New Jersey 07733.

Received June 23. 1981.

The complexity of computer-generated scenes is often greater than the display can handle. As a result, it is important to be able to select a subset of the scene which is appropriate for display. Without this subset filtering, small objects are aliased, producing Moire patterns, flickering, and other disturbing display artifacts. Presented are a scene representation and an associated display algorithm that together provide ease of subset filtering. The scene is hierarchically constructed and the filter selects an appropriate subtree of the hierarchy for display. The bottom nodes of the display subtree are visually faded with their parent nodes to produce a pleasing fade-out of objects that approach the limit of resolution. Combined with conventional anti-aliasing, this technique produces satisfying images, both still and animated, of scenes with a wide range of detail.

A New Lineur Algorithm for Intersecting Convex Polygons. JOSEPH O’ROURKE, CHI-BIN CHIEN, THOMAS OLSON, AND DAVID NADDOR. Electrical Engineering Department, The Johns Hopkins University, Baltimore, Maryland 2 12 18.

Received July 23, 198 1; revised October 8, 198 1.

An algorithm is presented that computes the intersection of two convex polygons in linear time. The algorithm is fundamentally different from the only known linear algorithms for this problem, due to Shamos and Hoey. These algorithms depend on a division of the plane into either angular sectors (Shamos) or parallel slabs (Hoey), and are mildly complex. Our algorithm searches for the intersection points of the polygons by advancing a single pointer around each polygon, and is very easy to program.

Aduptive Bit Allocution for Image Compression. J. K. WV AND R. E. BURGE. Physics Department, University of London, Queen Elizabeth College, Campden Hill Road, London W8 7AH, England.

Received July 30, 198 1; revised September 28, 198 I.

The key to producing data-compressed images of improved fidelity (at a given compression ratio) using the adaptive-transform approach is to improve subimage classification. Three simple measures are introduced to minimize inner-class differences based on image energy, directionality and fineness of local detail. A fast compression scheme incorporating these measures is illustrated by a range of examples.

Vectorizution of Ruster Images Using Hierurchciul Methods. L. GIBBON AND D. LUCAS. Interactive Systems Corporation, 5500 South Sycamore Street, Littleton, Colorado 80120.

Received August 17, 1981; revised September 18, 1981.

A method of line and edge following is presented which uses aggregate representations of pixel data instead of the pixels themselves. This method is being applied in the area of raster to vector conversion of maps and engineering drawings.

Runk Filters in Digitul Image Processing. GEORG HEYGSTER. Rechenzentrum der Universitat, 2800 Bremen 33, Germany.

Received August 19, 1981.