Re: Questions about equations of Shape Descriptors

Posted by vischer on Feb 26, 2010; 12:39am
URL: http://imagej.273.s1.nabble.com/Questions-about-equations-of-Shape-Descriptors-tp3688338p3688341.html

The area of an irregular roi, and that its of best-fitting ellipse, are the same (so are their moments of inertia).


Unfortunately, the equation

>> roundness = 4*area/(π*sqr(major axis))

has slipped into the documentation ages ago. It is correct, but it simply says:

 roundness = minor/major.

The "sqr" in the above equation does mean "square" (though it's not macro syntax).
Major axis and max Feret diameter are not the same. The best-fitting ellipse is a much more robust measurement than the Feret diameter, as all pixels inside an object are taken into account, not only the perimeter pixels.

Norbert Vischer