Reference Manual
Chapter
5
IVC-2D
©
SICK AG • Advanced Industrial Sensors • www.sick.com • All rights reserved
239
Blob Analyzer Setup
Blob Orientation and Bounding Box:
There are two
Blob Orientation Methods
to calculate the orientation of a blob. The
Area
Based
method calculates the orientation based on all the pixels in the specific blob, while
the
Boundary Based
only uses the pixels on the external perimeter of the blob. An XY-
bounding box is always computed (based on results from the Left Edge, the Top Edge, the
Width and the Length) and is drawn if no blob orientation method is chosen.
Which method will be best suited for your application depends on the shape of your blobs.
For a rectangular blob containing holes, the boundary-based method is most suitable. For
solid objects of arbitrary shapes the area-based method is often good. For perfect circles
and squares it is not possible to calculate an orientation since they have no orientation.
In the
Compute
Bounding Box
field, choose if to calculate a boundary box and if to visual-
ize it. The bounding box will get different colors depending on which blob orientation
method is selected. The
Boundary Based
method renders green boundary boxes, the
Area Based
method yellow, and if no blob orientation method is active the box will be
blue.
Blob Shape Features
The
Compute Blob Diameters
measure computes the maximum, the minimum and the
average diameters of the blob. It is only relevant for fairly circular blobs, since there simply
is no reasonable definition of diameter of, for example, a U shaped object. The measured
values are obtained by computing the diameter for all lines through the centroid of the
blob, starting and stopping at the two most distant points in the blob.
The
Compute Blob Perimeter
measure computes the length of the external perimeter of
the blob. Computing the perimeter length in a discrete image is an ambiguous task. The
measure returned by this function is fairly invariant to orientation, but the value may vary
with a few pixels from one scan to another on apparently identical objects due to sensor
noise, lighting conditions etc.
Visualize This Blob in Interactive Setup
Click the
<<
and the
>>
buttons to navigate between the blobs in the image, or enter a
Blob
Index
number.
The visualization in the interactive setup is different from the visual results you get when
executing the Blob Analyzer step in RUN or DEBUG mode. The visual representation of the
results are interpreted as follows:
•
The currently examined blob is green.
•
All other blobs are red.
•
The centroid of the currently examined blob is displayed as a red + sign.
•
All other blob centroids are displayed as signs.
The blob visualization is only a setup aid. It is not related to which blob that is analyzed
when the tool executes. This means that you can visualize one blob in the interactive setup
when configuring the tool, but use other blobs when running the program.
The image is by default stretched to fill the preview window. Click the
Fit to Window
button
to toggle between showing a stretched image and showing the image in its original size.
The stretching does not preserve the aspect ratio of the image. It is only when showing the
image in its original size that one pixel on the screen represents one pixel of the image.
Note:
