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Image Pr ocessing Systems 111

integrate new modules or construct metamodules that control exist-
ing IDRISI modules via a scripting language such as Visual Basic,
Delphi, or Visual C++. Even the menu system can be completely
reconfigured. Over the years this system has undergone drastic
expansion and improvement. It has evolved from a system excellent
for teaching the principles of digital image analysis to a professional
system suitable for practical production of image analysis results at
the industry standard. Its wide use by government agencies, schools,
research institutions, academia, and the private sector testifies to its
popularity (Simonovic, 1997).
Originating from a desktop system, IDRISI used to have a limited
capacity to handle large image files. Now this limitation has largely
disappeared with the improved functionality of personal computers.
However, other limitations persist, such as the legacy of the highly
modulized structure in which each module performs a narrowly
defined step. This design philosophy may be ideal for teaching the
concept of image processing, but is ineffective for practical produc-
tion because a number of modules are needed to perform a simple
analytical task such as image classification. The second critical limita-
tion of IDRISI is its lack of automation. Although the Macro Modeler
is a kind of scripting language for speeding up the process, it is not
applicable to all functions. Besides, processing speed is slow for cer-
tain functions such as zoom on screen (Huber, 2000). Finally, IDRISI
still lacks data preparation functions, such as its inability to orthorec-
tify images or georeference data using sensor-specific models. In spite
of its comprehensive range of image classifiers, it is not possible to
classify images based on pixel spatial properties and using external
knowledge.

4.2 ERDAS Imagine
ERDAS is one of the oldest and leading geoinformatic software
companies. Its major product, Imagine, contains a suite of compre-
hensive and sophisticated tools for digital analysis of remotely
sensed data. The latest release, version 9.1, offers something for
everyone: 3D feature extraction, terrain modeling, hyperspectral
data analysis, publication of 3D interaction environments, in addi-
tion to photogrammetric tools after the company was acquired by
Leica. This version significantly improves the integration of remote
sensing and photogrammetry with the addition of the Leica Photo-
grammetry Suite (LPS). Both Imagine and LPS can be configured to
work closely with Oracle 10g Spatial and/or ESRI’s ArcSDE (Cothren
and Barnes, 2006). The revamped ERDAS Imagine is offered at three
levels, Essentials, Advantage, and Professional. Imagine Essentials
encompasses a set of powerful tools for manipulating geographic
and imagery data, such as image georeferencing, visualization, and
map output. Imagine Advantage extends the capabilities of Imagine