Reference Manual
Chapter
4
IVC-2D
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SICK AG • Advanced Industrial Sensors • www.sick.com • All rights reserved
85
Edge
Find Line Edge
This tool finds edges on a user defined straight line by evaluating how the gray scale
changes along the line. There is an interactive setup and it is recommended to use it to set
the parameters. Double-click the Setup button to open the interactive setup. For more
information on the interactive setup, see on page 218.
There are two evaluation methods to detect transitions/changes of the gray scale.
Evaluation Method 1: Detect Relative Change of Gray Scale
Beginning at the starting point of the line this method detects the first change in the gray
scale that is above the user defined value. The evaluation is based on the derivation of the
histogram along the line. If the first absolute value of the derivation, average out of 4 pixels,
is greater or equal to the user defined threshold the function terminates. In that case the
function returns the coordinates of the first found pixel (
X transition
,
Y transition
).
Figure – Evaluation method 1: Detect relative change of gray scale
The figure above shows an example of evaluation method 1. The pixel with the first absolu-
te relative change of gray scale (in direction of evaluation) that is greater or equal to the
threshold is detected. In this case the amount of the last change is
≥
than the threshold.
The red circle indicates the detected point on the blue line. This point corresponds to the
location of the returned X and Y pixel coordinates. Red circle displayed in this example
only.
Evaluation Method 2: Detect Absolute Change of Gray Scale
Beginning at the starting point of the line this method detects if the gray scale enters a
user defined region of gray scale values. The evaluation is based on the absolute values in
the histogram along the line. The region of gray scale values is defined by upper and lower
thresholds. In this mode the function returns each transition into the region of gray scale
values. Note following convention: If the value of the gray scale the starting point of the line
is already in the region of gray scale the starting point itself is a detected point as well. In
this mode the function writes the found pixel coordinates of detected transitions into the
table.
The figure below shows an example of evaluation method 2. The red circles indicate the
detected points in the histogram (green line). Note that only one transition of the gray
scale into the selected region of gray scale is detected. This is due to the fact that the
location of the detected points depends on the direction of evaluation. The red circles
correspond to the location of the returned X and Y coordinates. Red circles displayed in
this example only.
Gray value along the line
User defined threshold of the minimal
required change of gray scale
Absolute derivative of the gray levels (shows
amount of gray scale changes along the
line)
Direction of evaluation
