EDGE DETECTION
A Challenge for Computer Vision
The difficulty of making computers see seems puzzling, given how easy
the task is for people and animals. To provide an appreciation of the
difficulty we show some examples of edge detection, a
process that is often used as the first step in Computer Vision.
The first step in understanding what is in a picture is to find outlines
of objects and edge detection does that by finding pixels where there
is a high contrast in color and/or brightness. Below is a picture of a
desk with a coffeepot on it. (See credits for the
source of this image as well as the rest of the images in this lecture.)
Here are the results of an edge detection program.
Parts of the outline of the coffeepot are missing and there are a lot
of lines not belonging to any significant object. Changing the program
that does the edge detection does not help much.
Edges
detected with another method.
The results are even worse when we deal with natural images, such as
that of the tiger below.
Can you find the tiger amongst the edges below?
Edges detected with
another method. Changing the method does not help much. You get
a lot of lines, some corresponding to the outline of a significant object,
most to the background.
Why people are very good in seeing the tiger right away? (Hint:
grrr)
A good discussion of methods of edge detection can be found in a web
site titled Edge
Detector Comparison. It is based on work done at the University of
South Florida by a group that was led by professor Kevin Bowyer. (The
site describes work carried out about ten years ago. Professor Bowyer
is now at the University of Notre Dame.) All the pictures in this page
have been taken from that site.
You can peruse more examples by going to that page and then clicking
over one of the displayed thumbnail images. The result will be a full
size image (in grey scale) with a table of links below. The columns are
labeled with the name of the person who developed the method and the rows
correspond to diffeerent parameter selected for the task.
Updated March 9, 2007
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