Setting the Conditions for Each Object Type
3-25
3
(7) Edge detection
The "edge" refers to the boundaries between the brighter (white) and darker (black) parts in an image.
The "edge detection" function is used to detect this boundary by processing the image.
An example of detecting a point using the edge detection function and user specified
criteria
- The edge detection point coordinates are used as a reference point to detect an out of position
condition.
- Edge detection in binary images is much quicker than in a gray scale search. However, the binary
image detection process is less precise at detecting position.
A
Edge detection point
Edge detection
point
B
A
B
A
Light
↑
Brightness
level
↓
Dark
Light
↑
Brightness
level
↓
Dark
Direction
B
Edge
width
Flat
width
A
B
A
B
A
Difference
in level
Direction
Edge
width
Flat
width
Difference
in level
B
Detection direction
Detection direction
Detection area
Detection area
• Horizontal transition point
from light to dark (moving
from left to right)
• Vertical transition point
from light to dark (moving
from top to bottom)
• Horizontal transition point
from light to dark (moving
from right to left)
Edge detection point
Detection area
• Center (dark), horizontal (left and right)
• Vertical transition point
from light to dark (moving
from bottom to top)
Detection
direction
Detection
direction
Internal diameter (between B and C)
External diameter (between A and D)
Detection area
• Edge detection of the inside and outside edges of a two circles
A: Moving right horizontally
from light to dark
B: Moving right horizontally
from dark to light
C: Moving left horizontally
from dark to light
D: Moving left horizontally
from light to dark
Edge detection
point
