Page 160 - Digital Analysis of Remotely Sensed Imagery

Image Pr ocessing Systems 127

is able to handle images as large as 500 Mb. This limit disappears in
the enterprise version. The web server requires an image compres-
sion plug-in installed in the client’s machine before it can function
properly. Prior to image delivery via the Internet, the server first com-
presses the image in one of the two formats: the ECW (enhanced
compressed wavelet) and JPEG 2000. Large image data can be com-
pressed or uncompressed using the compression wizard. A compres-
sion ratio of 10:1 to 15:1 is achievable for grayscale imagery. The
quality of color imagery can still be very high after being compressed
at a ratio of 25:1 to 50:1.
Once accessed, images can be browsed via web pages. Certain
applications, such as ArcGIS, may require the installation of special
software. In addition, a number of plug-ins freely available from the
ER Mapper Web site allow users to interact with images on the Inter-
net server in Microsoft Windows applications, ArcView, MapInfo,
and so on (Qiu and Thrall, 2006). Unlike other similar systems, ER
Mapper’s web server does not require any processing on the client
side, such as loading up image pyramids. Images may be panned,
zoomed in and out freely, but not scrolled using the mouse, a feature
that is not supported at present. Besides, errors are resulted if the cli-
ent has a display larger than 1600 by 200 pixels. This server allows
seamless integration of various types of 2D and 3D raster images
with such GIS web applications as ArcIMS, Tiger, and Map Server.
Thus, ER Mapper image web server is fully compatible with all indus-
try standard image-serving protocols. To be launched in the image
web server is the RightWebMap function that is able to integrate mul-
tiple GIS and image services into a single application view.

4.4.5 Evaluation
ER Mapper has the most friendly user interface thanks to the wide-
spread use of interactive wizards that automate common and complex
tasks, such as image mosaicking, image enhancement and compres-
sion, and batch conversion. These wizards also simplify complex image
processing tasks. Consequently, even novice users can take full
advantage of functions on offer by the system. ER Mapper possesses
a comprehensive range of image processing functions. Its image dis-
play functions are especially powerful among major image process-
ing packages. This system allows dynamic integration of data of
various types and spatial resolution without the need to unify cell size
(Civco, 1996). Similar to ERDAS, this truly open and user-extensible
system enjoys an unrivalled advantage in image processing speed.
It is rather competent at handling large image files, and is able to
mosaic a large number of images quickly. It used to have a limited
capacity for integration with vector data. This drawback has mostly
disappeared in the new release. Perhaps the most distinct strength of
ER Mapper is its image web server that enables images to be deliv-
ered, shared, and increasingly manipulated over the Internet and