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Image Pr ocessing Systems 117

detection are presented in a user-friendly manner. Change may be
detected in two modes: a broad area search and site monitoring. In
the first mode, change pixels are highlighted across the entire scene.
In the second mode, change in the user-specified areas is visualized
and explored from the differencing image after significant changes
have been distinguished from insignificant ones using spatial filter-
ing or thresholding. The user is able to identify and focus on changes
that are of special interest to a particular application.
ERDAS Imagine also contains a Developers’ Toolkit that allows
the user to modify the commercial version of Imagine, or to develop
entirely new applications as extensions, using a set of libraries and
documentation. Several packages in the Toolkit support a number of
routines, such as abstract object manipulation, file I/O and system
access, GUI access, 2D and 3D visualization. Recently, ERDAS has
acquired ER Mapper, so it offers more modules than can be described
here.
4.2.8 Documentation and Evaluation
ERDAS Imagine provides a wide variety of means for user support,
including on-screen help, Field Guide and tutorials. The help button
is ubiquitously displayed at every menu and in every operation win-
dow. A detailed explanation of the functions of each module in the
menu pops up upon clicking the help button. If this button is located
in an operation window, the displayed message explains how to
interact with the system. Such information in the hyperlinked text
format is very helpful for new users of the system. More information
on a specific topic can be found by clicking the highlighted phrases in
the message. Through the HTML help message, it may be possible to
navigate to the online Imagine interface manual and the Field Guide.
The manual illustrates how to interact with a tool window once it is
activated (e.g., how to enter the appropriate parameters in the boxes
in a function window).
The ERDAS Field Guide presents more theoretic background on
special processing methods or algorithms used in Imagine. Formerly
written in HTML, the guide allowed the search for a special topic
thanks to the use of indexing. Sadly, it is almost impossible to search
through the document for a specific topic anymore, due to the PDF
format adopted. Additionally, ERDAS also provides the user with a
790-page Tour Guide organized in hierarchical form. Contained in
this manual are step-by-step instructions on how to operate the sys-
tem to perform a specific image analysis task, supplemented with
screen-captured illustrations. All major modules are covered in this
manual.
The strength of ERDAS Imagine lies in its comprehensiveness
and its ability to integrate digital image analysis with photogram-
metry and GIS. Its collection of toolboxes, the largest in the industry,
is able to perform nearly all kinds of image analyses, ranging from