Banner PresencePLUS P4 Series - Manual (Page 116)

Discard Boundary Blobs: The Discard Boundary Blobs checkbox, if selected, allows you to determine if you
want blobs touching the perimeter of the search ROI to be included in your results.
Fill Holes: Fill Holes checkbox, if selected, allows you to ignore (by filling) small features such as scratches,
glare and so on which might otherwise appear as small imperfections or non-blobs within a larger blob. If you
select this option, you can specify the size of the largest hole to fill in the Largest Hole to Fill field.
Compute Statistics: The Compute Statistics checkbox, when selected, enables advanced results to be
calculated and displayed when inspections are run.
Largest Hole to Fill: If you select Fill Holes, you must specify the size of the largest hole to fill in this field.
Blob Detect Tool Advanced Tab Results
Area
The area (A) is just a count of the total number of pixels belonging to the blob.
Centroid
The centroid (x
c
, y
c
) is the point at the center of mass of the blob. For simple blobs like solid circles, ellipses,
or rectangles, this is just the center of the shape. For more complicated shapes it is helpful to imagine a piece
of cardboard cut out in the shape of the blob. The centroid is the point where you could balance the cardboard
on the tip of a pencil. For complicated shapes-especially shapes with unfilled holes-the centroid might lie
outside the shape.
The x coordinate of the centroid is calculated by adding up the x coordinates of each pixel in the blob and
dividing by the area. The y coordinate is similar:
Perimeter
The perimeter (P) gives an approximate measurement of the length of the circumference of the blob. Because
blobs are built from individual pixels, it is most practical to estimate the perimeter by counting the contributions
of individual pixels on the blob's boundary. The following table describes the exact values that are added to
the perimeter for each possible pixel configuration. In each example, the description refers to the center pixel
in the corresponding pictures.
A pixel with no neighbors that belong to the same blob contributes
(3.14) linear pixels to the perimeter of the blob. This can only
happen in a blob that has an area of one. Since such small blobs
are usually ignored, this circumstance is rare.
A pixel with one neighbor that belongs to the same blob
contributes 2.571 linear pixels to the perimeter of the blob.
A pixel with two neighbors that belong to the same blob, forming
a straight line, contributes exactly 2 linear pixels to the perimeter
of the blob.
P/N 000000 Banner Engineering Corp. - Minneapolis, MN USA - www.bannerengineering.com
Tel: 763.544.3164
116
7/2009 PresencePLUS Software Tools