The Efficiency of Portable Image Processing Software

It is a common opinion in the image processing field that a software system cannot be both portable and efficient. Furthermore, when efficiency prevails in the design of an image processing system, the system typically becomes hard to use and complicated to program in. Most efficient systems require the user to worry about external data format, buffer allocation, overlapped input and output and similar details. To show that it is feasible to design an image processing system that is efficient, portable and easy to use, a system has been designed and implemented using the "Software Tools" philosophy. This system has been implemented on two computer systems (the PDP-11 and the VAX-11) under three different operating systems (Unix, RSX-11M and VMS). The image operations have been implemented in Ratfor with the bulk of the image i/o routines written in C. Details such as double-buffered overlapped i/o, conversion of external data formats and virtual memory support (on the VAX-11) are handled automatically by the system. Additionally, the system allows one to perform image operations "on the fly" under Unix, allowing one to use software pipelines for image processing. It is shown that this system is portable and efficient. The system is analyzed to determine where the time is spent during typical image operations. This analysis shows that the features that make the system easy to use account for a small fraction of its time. The performance of the system is also measured under different operating systems