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Title
Proceedings of the Symposium on Global and Environmental Monitoring

168
A HIERARCHICAL TERRAIN INTERPRETATION SYSTEM
USING ’PIXEL SWAPPING’ METHOD
Joji Iisaka
Canada Centre for Remote Sensing
1547 Merivale Rd. Nepean, Ontario, Canada
Wendy Russell
Intera Technologies Ltd.
Ottawa, Ontario, Canada
ABSTRACT
Digital image processing is very popular for extracting terrain information from remotely sensed data. At
present, most image analysis methods are still limited to the processing of images on a pixel-by-pixel basis while
the human interpretation of images is mostly based on structural spatial information with a high level of context
and semantics. This paper briefly describes the concept of the microcomputer-based terrain understanding
system which employs hierarchical image interpretation steps using the ’pixel swapping’ method.
The ’pixel swapping’ method provides a unified image analysis method for spectral and spatial features in
images. Image interpretation steps are divided hierarchically into a bottom-up and top-down approach. Each
involves a few steps. With the bottom-up approach, an image is analyzed first by traditional low-level
processing methods using numerical pixel values. The results of the numeric interpretation are interpreted in
a more symbolic way by applying the ’pixel swapping’ method of spatial interpretation. The symbolized images
are interpreted based on the type of the attributes, constraints of the attribute values, and the spatial relations
between various objects in images.
On the other hand, the targeted object in an image is divided into its constituent components and their
attributes under the top-down approach. The system gives the control to the lower levels to evaluate required
attribute values, if they have not been evaluated before, and compares the estimated attribute values with
existing knowledge of the attributes in a data base.
The system employs an LSI-based image processor (IP9506) to accelerate low-level image processing and to
facilitate the implementation of pixel swapping.