Select this parameter to compute the perimeter of polygons formed by the outlines of the objects. If the image is spatially calibrated, the outline perimeter will be calculated in calibrated units. In general, the outline perimeter is somewhat less than the pixel-based Perim due to the fact that the outlines are considered to be passing through the centers the boundary pixels rather than encompassing them. For example, if the object is a 5 by 5 block of pixels, it will be considered 4 pixel width wide and 4 pixel heights tall, so its outline perimeter will be 16 geometrical units as opposed to 20 ones given by the pixel based Perim.
If objects contain holes, the holes are disregarded and the internal boundaries are not included in the calculations.