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8 Image Processing

8.1 Introduction

Computer graphics are stored and processed either as vector or raster data.
Most data types that were encountered in the previous chapter were vector
data, i.e., points, lines and polygons. Drainage networks, the outline of geo-
logic units, sampling locations and topographic contours are examples of
vector data. In Chapter 7, coastlines are stored in vector format while bathy-
metric and topographic data are saved in the raster format. In many cases,
vector and raster data are combined in one data set, for instance the course
of a river is displayed on a satellite image. Raster data are often converted to
vector data by digitizing points, lines or polygons. On the other hand, vector
data are sometimes transformed to raster data.
Images are generally represented as raster data, i.e., as a 2D array of color
intensities. Images are everywhere in geosciences. Field geologists use aeri-
al photos and satellite images to identify lithologic units, tectonic structures,
landslides and other features in a study area. Geomorphologists use such
images for the analysis of drainage networks, river catchment, vegetation
and soil types. The analysis of images from thin sections, automated identi-
fication of objects and the measurement of varve thicknesses employ a great
variety of image processing methods.
This chapter deals with the analysis and display of image data. Firstly,
the various ways that raster data can be stored on the computer are explored
(Chapter 8.2). Subsequently, the main tools for importing, manipulating and
exporting image data are presented (Chapter 8.3). This knowledge is used
for processing and georeferencing satellite images (Chapter 8.4 and 8.5).
Finally, on-screen digitization techniques are discussed (Chapter 8.7). The
Image Processing Toolbox is used for the specific examples throughout the
chapter. The image analysis and enhancement techniques discussed in this
chapter are also presented in the User·s Guide. However, this chapter con-
tains a comprehensive introduction to the techniques for analyzing images
in the earth sciences by using MATLAB.