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The detection of the isolated points in an image is straightforward. Using the mask shown in Fig
2, a point has been detected at the location on which the mask is centered if
where T is a nonnegative threshold , and R is given by Eq given above.
-1 -1 -1
-1 8 -1 -1 -1 -1
Fig 2: A 3*3 mask used for detecting isolated points
The gray level of an isolated point will be quite different from the gray level of its neighbors
and this formulation will measure the weighted differences between the center point and its
-1 -1 -1 2 -1 2 -1 2 -1 -1 2 2 2 -1 2 -1 -1 2 -1 -1 2 -1 -1 -1 -1 2 -1 -1 -1 2 -1 -1 -1 2 Horizontal +450 Vertical -450 Fig 3 : Line masks
The preferred direction of each mask is weighted with a larger coefficient than other possible
directions. Let R1, R2 , R3 and R4 denote the responses of the masks in the Fig 3 above from
left to right, where the R’s are given by equation above. Suppose that all masks are run through
an image. If, at a certain point in the image, ⏐ Ri⏐>⏐Rj⏐, for all j≠i, that point is said to be more
likely associated with a line in the direction of mask i.
Faculty of Engineering Robotics Technology MECH 4041 3
B.Eng (Hons.) Mechatronics S. Venkannah Mechanical and Production Engineering Department An edge is the boundary between two regions with relatively distinct gray-level properties. In
the following discussion, the assumption is that the regions n question are sufficiently
homogeneous so that the transition between two regions can be determined on the basis of gray
level discontinuities alone. When this assumption is not valid other segmentation techniques
discussed later must be used.
Basically, the idea underlying most edge-detection techniques is the computation of a local
derivative operator. Fig 4 illustrates t his concepts. Fig 4 (a) shows an image of a light stripe on
a dark background, the gray level profile along a horizontal scan line of the image, and the first
and second derivatives of the profile. Note from the profile tha...
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This document was uploaded on 03/12/2014 for the course MECHANICAL 214 at University of Manchester.
- Spring '14