Page 155 - Digital Analysis of Remotely Sensed Imagery

Image Pr ocessing Systems 123

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ENVI 4.4 has drastically expanded image processing capabilities
and successfully overcome the limitations of previous releases with
the addition of a few modules. Its simplified user interface is easy to
operate with a high degree of automation, thanks to the logic layout
(Thurston, 2008). The newly added tools make common image pro-
cessing tasks, such as working with vector layers, pan-sharpening
images, and change detection, quickly and efficiently performed. In
particular, the SPEAR tools facilitate development of quick applica-
tions, and support existing libraries of feature extraction. ENVI 4.4
offers additional spectral processing and analysis functions—the core
capabilities that make ENVI the choice of geospatial professionals
around the world.
As an important image analysis system, ENVI offers a wide range
of traditional and nontraditional image classifiers. For instance, it is
one of the earliest systems with the capability of image classification
based on machine learning. At present ENVI is able to classify images
using neural network and binary encoding, but not knowledge-based
methods. Nor does it have a strong capability of integrating image
analysis with GIS, even though this weakness has been minimized in
the recent release of ENVI. Written in the powerful structured Interac-
tive Data Language (IDL), which is required to run ENVI, ENVI is
highly flexible and dynamic. However, the operation of ENVI can be
further improved via better organization of some functions such as
image display, which is spread into several places. Graphic icons may
be added to accompany the functions in the toolbar for quick access.

4.4 ER Mapper
Founded by Stuart Nixon, ER Mapper is an Australian software com-
pany specializing in digital image analysis. Its major product of the
same name is a powerful window-based imagery analysis package
that offers a complete suite of image processing tools. Its latest release,
version 7.0, is one of the industry’s leaders in image analysis. ER Map-
per is offered to the public at two levels: desktop and enterprise. The
former contains such modules as Professional, Image Viewer, and
Compressor, the first being the flagship product. The later includes
Image Web Sever. These important modules are introduced below.

4.4.1 User Interface, Data Input/Output and Preparation
Similar to all other systems, ER Mapper has an icon-driven user inter-
face. Once the system is activated, a panel of toolbars is displayed at
the top of the screen (Fig. 4.4). Contained in the panel are modules for
image display (View), editing (Edit), and processing (Process), apart
from a few utility buttons such as file, toolbar, utilities, and help.