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Azriel Rosenfeld

Opinion Mar 1 1995

To take arms against a sea of email

The rapid growth of the Internet means there is more email traffic now than ever before, and there will be still more in years to come. There was a time when only hard-core hackers had to deal with significant amounts of email. As email becomes a standard medium of communication, and more and more nonprogrammers join mailing lists, an increasing number of people find themselves receiving large amounts of email and must cope with it.
Computing Applications

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Research and Advances Mar 1 1980

Region representation: boundary codes from quadtrees

There has been recent interest in the use of quadtrees to represent regions in an image. It thus becomes desirable to develop efficient methods of conversion between quadtrees and other types of region representations. This paper presents an algorithm for converting from quadtrees to a simple class of boundary codes. The algorithm is shown to have an execution time proportional to the perimeter of the region.
Research and Advances Nov 1 1979

Breaking substitution ciphers using a relaxation algorithm

Substitution ciphers are codes in which each letter of the alphabet has one fixed substitute, and the word divisions do not change. In this paper the problem of breaking substitution ciphers is represented as a probabilistic labeling problem. Every code letter is assigned probabilities of representing plaintext letters. These probabilities are updated in parallel for all code letters, using joint letter probabilities. Iterating the updating scheme results in improved estimates that finally lead to breaking the cipher. The method is applied successfully to two examples.
Research and Advances Feb 1 1978

Some new methods of detecting step edges in digital pictures

This note describes two operators that respond to step edges, but not to ramps. The first is similar to the digital Laplacian, but uses the max, rather than the sum, of the x and y second differences. The second uses the difference between the mean and median gray levels in a neighborhood. The outputs obtained from these operators applied to a set of test pictures are compared with each other and with the standard digital Laplacian and gradient. A third operator, which uses the distance between the center and centroid of a neighborhood as an edge value, is also briefly considered; it turns out to be equivalent to one of the standard digital approximations to the gradient.
Artificial Intelligence and Machine Learning
Research and Advances May 1 1973

An array grammar programming system

A package of Fortran programs has been developed that permits a user to interactively design and test array grammars. The user can control the rule selection procedure in a derivation or parse, using weighted programming matrices; he also has a choice of instance selection schemes (raster, random, parallel). Examples are given involving array languages consisting of simple geometrical patterns, as well as a language of “neuron pictures.”
Research and Advances Apr 1 1973

A region coloring technique for scene analysis

A method of converting a picture into a “cartoon” or “map” whose regions correspond to differently textured regions is described. Texture edges in the picture are detected, and solid regions surrounded by these (usually broken) edges are “colored in” using a propagation process. The resulting map is cleaned by comparing the region colors with the textures of the corresponding regions in the picture, and also by merging some regions with others according to criteria based on topology and size. The method has been applied to the construction of cloud cover maps from cloud cover pictures obtained by satellites.

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