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Research and Advances May 1 1986

TID—a translation invariant data structure for storing images

There are a number of techniques for representing pictorial information, among them are borders, arrays, and skeletons. Quadtrees are often used to store black and white picture information. A variety of techniques have been suggested for improving quadtrees, including linear quadtrees, QMATs (quadtree medial axis transform), forests of quadtrees, etc. The major purpose of these improvements is to reduce the storage required without greatly increasing the processing costs. All of these methods suffer from the fact that the structure of the underlying quadtree can be very sensitive to the placement of the origin. In this paper we discuss a translation invariant data structure (which we name TID) for storing and processing images based on the medial axis transform of the image that consists of all the maximal black squares contained in the image. We also discuss the performance of TID with other existing structures such as QMATs, forests of quadtrees, and normalized quadtrees. Some discussion on the union and intersection of images using TID is included.
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Research and Advances Apr 1 1986

A locally adaptive data compression scheme

A data compression scheme that exploits locality of reference, such as occurs when words are used frequently over short intervals and then fall into long periods of disuse, is described. The scheme is based on a simple heuristic for self-organizing sequential search and on variable-length encodings of integers. We prove that it never performs much worse than Huffman coding and can perform substantially better; experiments on real files show that its performance is usually quite close to that of Huffman coding. Our scheme has many implementation advantages: it is simple, allows fast encoding and decoding, and requires only one pass over the data to be compressed (static Huffman coding takes two passes).
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Research and Advances Mar 1 1986

Andrew: a distributed personal computing environment

The Information Technology Center (ITC), a collaborative effort between IBM and Carnegie-Mellon University, is in the process of creating Andrew, a prototype computing and communication system for universities. This article traces the origins of Andrew, discusses its goals and strategies, and gives an overview of the current status of its implementation and usage.

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