Stephen James Todd

Parameter reduction and context selection for compression of gray-scale images

In the compression of multilevel (color or gray) image data, effective compression is obtained economically by judicial selection of the predictor and the conditioning states or contexts which determine what probability distribution to use for the prediction error. We provide a cost-effective approach to the following two problems: (1) to reduce the number of coding parameters to describe a distribution when several contexts are involved, and (2) to choose contexts for which variations in prediction error distributions are expected. We solve Problem 1 (distribution description) by a partition of the range of values of the outcomes into equivalence classes, called buckets. The result is a special decomposition of the error range. Cost-effectiveness is achieved by using the many contexts only to predict the bucket (equivalence class) probabilities. The probabilities of the value within the bucket are assumed to be independent of the context, thus enormously reducing the number of coding parameters involved. We solve Problem 2 (economical contexts) by using the buckets of the surrounding pixels as components of the conditioning class. The bucket values have the desirable properties needed for the error distributions.

The Peterlee relational test vehicle: a system overview

A high-level data-base system, the Peterlee Relational Test Vehicle (PRTV), provides flexible, interactive data-base support and functional extensibility. The user sees the system primarily through a programming language called ISBL, which is designed for manipulating bulk data held in relations. PRTV is not a fullfledged data-base system, but rather an evolving prototype which is expected to aid in solving some of the problems that have been encountered in using relational data bases. PRTV embodies research both in data-base language design and in efficient implementation techniques.

JANUS: An interactive system for document composition

This paper describes the architecture of a proposed document composition system named JANUS, which is intended to provide support for authors of complex documents containing mixtures of text, line art, and tone art. The JANUS system is highly interactive, providing authors with immediate feedback and direct electronic control over page layouts, using a special two-display workstation. Authors communicate with the system by marking up their documents with high-level descriptive “tags”. A tag definition language is provided whereby new tags may be defined and the format of each tagged object may be controlled.

The WINSOM solid modeller and its application to data visualization

The IBM United Kingdom Scientific Centres WINchester SOlid Modelling system (WINSOM) is a set-theoretic, constructive solid geometry (CSG) modeller based on recursive division techniques. It specializes in handling complex models and provides graphical facilities intended for engineering applications. This paper describes WINSOM and some of the many programs that are linked to it, and gives examples of their application to problems of data visualization.

The Winchester graphics system: a technical overview

This paper gives a technical overview of the Winchester Graphics System. It concentrates on the software system, and in particular, the use of a relational database (PRTV). The main use of the system is in scientific research and it has been used a great deal in Chemistry, Biophysics and related sciences. However, the facilities are general and the same system is used for quite different applications. such as engineering and archaeology. This database has been found to provide researchers with a powerful flexible tool and has helped the UKSC to provide an environment where new ideas can be proposed and evaluated quickly and easily.

Arithmetic codes for constrained channels

Arithmetic codes have been studied in the context of compression coding, i.e., transformations to code strings which take up less storage space or require less transmission time over a communications link. Another application of coding theory is that of noiseless channel coding, where constraints on strings in the channel symbol alphabet prevent an obvious mapping of data strings to channel strings. An interesting duality exists between compression coding and channel coding. The source alphabet and code alphabet of a compression system correspond, respectively, to the channel alphabet and data alphabet of a constrained channel system. The decodability criterion of compression codes corresponds to the representability criterion of constrained channel codes, as the generalized Kraft Inequality has a dual inequality due to the senior author.

The use of a relational data base for holding molecule data in a molecular graphics system

Abstract An n -ary relational data base system has been used to hold the molecule data of a high-level molecular graphics system. The data base management sy

The use of prolog as a protein querying language

Abstract PROLOG has been used to implement the knowledge base of a protein querying system. Its suitability for this application has been investigated as part o

System and method for controlling data storage in a data processing system in which objects generated within a lower level language program are associated with memory slots allocated to another program

A data processing system of the type in which a first program interacts with a second lower level language program is provided, the system includes a lower level language subroutine for generating objects within the second program, a memory for storing the objects, and an interface, object surrogates and surrogate references for associating the objects with one or more slots allocated to the first program. The interface is generated between the first and second programs by the first program, the interface residing within the first program. The object surrogates are then contained within the interface, each object surrogate containing an identifier for a given object. To associate one or more of the slots with a particular object surrogate, the surrogate references identifying the object surrogates are stored by the first program in those slots. During operation of the first program slots may be redefined by erasing old surrogate references and replacing them with different ones. When an object surrogate is no longer associated by any surrogate reference with any of the slots, then a high level language garbage collector informs the second program. By employing such an approach the data processing system is able to automatically keep track of objects, releasing the user from the burden of having to set up L.L.L. checking routines of his own, and further enabling the system to make much more efficient use of available memory.

Protein secondary structural representation using real-time interactive computer graphics

Abstract A method is described for generating schematic secondary structure representations of protein molecules, on a realtime interactive calligraphic display. This provides a particularly useful aid in the understanding of protein topology. The method also greatly facilitates comparison of the dispositions of secondary structural elements and motifs in related or functionally similar proteins.