Image Processing Reference
In-Depth Information
(a) Original image
(b) Vertical edges, Equation 4.1
(c) Horizontal edges, Equation 4.2
(d) All edges, Equation 4.4
Figure 4.2
First-order edge detection
by both the vertical and the horizontal operators and is therefore much brighter than the
other edge points. In contrast, the top left hand corner point is detected by neither operator
and so does not appear in the final image.
2
-1
-1
0
Figure 4.3
Template for first-order difference
The template in Figure
4.3
is convolved with the image to detect edges. The direct
implementation of this operator, i.e. using Equation 4.4 rather than template convolution,
is given in Code
4.1
. Naturally, template convolution could be used, but it is unnecessarily
complex in this case.
Uniform thresholding
(Section 3.3.4) is often used to select the brightest points, following
application of an edge detection operator. The threshold level controls the number of
selected points; too high a level can select too few points, whereas too low a level can
