LOW COST IMAGE PROCESSING ON PERSONAL COMPUTERS: 
THE MACINTOSH-II BASED DIRIGO SYSTEM 
Manfred Ehlers 
National Center for Geographic Information and Analysis (NCGIA) 
Department of Surveying Engineering 
University of Maine 
Orono, ME 04469 
E-Mail: ehlers@mecanl.bitnet 
ABSTRACT 
Interactive image processing systems for the analysis of remotely sensed data are readily 
available for IBM compatible PCs and various mini- and micro-computers. Image 
processing software to be used on Macintosh PCs, however, has usually been 
associated with desktop publishing or medical/biological applications. With the advent 
of standard color displays for the Macintosh II series, image processing systems could 
be expanded to include remote sensing applications. Combining the user-friendly 
Macintosh interface with the capability of displaying multispectral remote sensing image 
data offers the unique possibility of a 4th generation image processing system design. 
During a one-semester course in image processing, students of the Department of 
Surveying Engineering at the University of Maine designed and implemented the Dirigo 
software package for the analysis of remotely sensed data on an off-the-shelf Macintosh 
II. The students were assigned to teams, each tackling a specific component of the 
system. Coordination was maintained through status reports and intensive discussions 
and resulted in the integration of all application software components in one common 
user interface. 
Concentrating on the components necessary for remote sensing applications, Dirigo 
contains menus for (a) point operations; (b) spatial filtering; (c) geometric corrections 
and georeferencing; (d) multispectral classifications; and (e) general utilities (e.g. pan 
and zoom). The software was written from scratch using exclusively Macintosh intuitive 
tools for the interface design. This allows inexperienced users and computer novices to 
get familiar with the system quickly and avoids unnecessary overhead in the learning 
curve. 
This paper describes specifications and performance of the Dirigo system, compares it 
with existing software packages and outlines future developments. 
INTRODUCTION 
The past decade has witnessed rapid technological development in computing hardware 
producing continual reductions in the cost of systems. High level microprocessors in 
personal computers vastly outperform their forerunners of only a few years ago and 
challenge minicomputers in performance. Two manufacturers of high performance 
chips for the use in super microcomputers have established themselves as marketleaders, 
Intel and Motorola (Ferns and Press, 1988). The Intel 8()xxx series and the Motorola 
68xxx family are the most widely used and may be associated with the 'IBM world'