The perimeter of an object is expressed in pixels and represents the total number of pixels around the boundary of the object. The algorithm uses an 8-connected pixel connectivity method to calculate the perimeter of the object. In order to avoid significant over-estimation of the perimeter length, the algorithm uses a chain code algorithm which estimates 8-connected corners as the diagonal of a pixel rather than counting 2 complete pixel edges as seen in some simpler algorithms. The difference between a simple perimeter algorithm and the chain code method implemented in the MFI software can be seen in the figure.
The circularity of an object is expressed as a value between zero and one (unit-less) and represents the ratio of the circumference of an equivalent area circle over the measured perimeter. This calculation is based on the perimeter value explained above.
