Figure 3. Peripheral protrusions may not be included in the final contours.

The segmentation program can capture cell bodies and some parts of protrusion structures. However, peripheral protrusion structures with locally increased light intensity (marked by a red arrow in figure A) connected with thin extensions would not be included in the final contours (“A” in figure B). Similarly, thin lamellipodia of low image contrast would not be included in the final contours (“B” in figure B). Finally, the contour could not converge to a sharp protrusion structure due to the constraint of internal energy of the contour (“C” in figure B).