I've come across the image object properties, "extent" and "solidity."
Definitions are pretty straightforward to understand: Extent of an image object is defined as area of the image object divided by the area of its bounding rectangle. Solidity (convexity) of an image object is, area of the image object divided by area of its convex hull.
However, coming to think of these two properties in terms of the applicability, I can't seem to think how one would give an edge compared to the other. After a quick look-up of these terms, my thoughts are that solidity - as compared to extent - can be a good criteria of image object's roundness since the convex hull forms the minimum enclosing polygon around the object.
What other applications do these two terms have - in conjunction with each other or as building blocks for more advanced contour properties?