Introduction - Feature Extraction and Image Processing - page 3

Synthesised images are good for evaluating techniques and finding out how they work,
and some of the bounds on performance . Two synthetic images are shown in Figure 1.2 .
Figure 1.2 (a) is an image of circles that were specified mathematically . The image is an
ideal case: the circles are perfectly defined and the brightness levels have been specified to
be constant. This type of synthetic image is good for evaluating techniques which find the
borders of the shape (its edges), the shape itself and even for making a description of the
shape. Figure 1.2 (b) is a synthetic image made up of sections of real image data. The
borders between the regions of image data are exact, again specified by a program. The
image data comes from a well-known texture database, the Brodatz album of textures. This
was scanned and stored as computer images. This image can be used to analyse how well
computer vision algorithms can identify regions of differing texture.

(a) Circles (b) Textures

Figure 1.2 Examples of synthesised images

This chapter will show you how basic computer vision systems work, in the context of
the human vision system. It covers the main elements of human vision showing you how
your eyes work (and how they can be deceived!). For computer vision, this chapter covers
the hardware and software used for image analysis, giving an introduction to Mathcad and
Matlab, the software tools used throughout this text to implement computer vision algorithms.
Finally, a selection of pointers to other material is provided, especially those for more
detail on the topics covered in this chapter.

1.3 The human vision system

Human vision is a sophisticated system that senses and acts on visual stimuli . It has
evolved for millions of years, primarily for defence or survival. Intuitively, computer and
human vision appear to have the same function. The purpose of both systems is to interpret
spatial data, data that is indexed by more than one dimension. Even though computer and
human vision are functionally similar, you cannot expect a computer vision system to
replicate exactly the function of the human eye. This is partly because we do not understand
fully how the eye works, as we shall see in this section. Accordingly, we cannot design a
system to replicate exactly its function. In fact, some of the properties of the human eye are