The Halcon Vision System: An Example for Flexible Software Architecture

This paper presents a software architecture that is capable of easy extension and maintenance and enables the user to develop applications rapidly and in a flexible manner. This is achieved by using an object-oriented design, both for the data structures and the operators which process this data. The granularity of the operators is chosen such that they easily can be combined to solve various kinds of vision problems but on the other hand have an appropriate level of abstraction so that the user does not have to worry about low level vision. The data structures are designed such that they are easy to use but allow a high performance implementation. Based on these operators and data structures an interactive tool for rapid program development is realized. It helps the user in selecting appropriate operators in many ways. For example, the system provides context sensitive selection of possible alternative operators as well as suitable successors and required predecessors. For the task of choosing appropriate parameters several alternatives exist. For example, the system provides default values as well as lists of useful values for all parameters of each operator. To achieve this, a knowledge base containing facts about the operators and their parameters is used.