http://imagej.273.s1.nabble.com/possible-error-in-docs-tp5017241p5017243.html
> Hi Aryeh,
> The area of an ellipse is: PI*(major/2)*(minor)/2
>
> So the roundness would be: Area/(PI*major^2) =( 4*(major/2)(minor/2)
> )/ PI*major^2
>
> And the 4 cancels out - what you get for the roundness is
> minor/major. This is 1 for a perfect circle.
>
> Does this help?
> Avital
>
> On Mon, Sep 26, 2016 at 3:07 PM, Aryeh Weiss <
[hidden email]
> <mailto:
[hidden email]>> wrote:
>
> I was looking for how ImageJ calculates roundness, and I found the
> following:
> /
> Shape descriptors/ Calculates and displays the following shape
> descriptors:
>
> *
> /Circularity/ /4/π/ × [/Area/][/Perimeter/]^2 / with a value of 1.0
> indicating a perfect circle. As the value approaches 0.0, it
> indicates an increasingly elongated shape. Values may not be valid
> for very small particles. Uses the heading*Circ*.
> *
> /Aspect ratio/ The aspect ratio of the particle’s fitted ellipse,
> i.e., [/Major/ /Axis/][/Minor/ /Axis/]. If */Fit Ellipse/* is
> selected the*Major* and *Minor* axis are displayed. Uses the
> heading*AR*.
> *
> /Roundness/ 4 × [/Area/]/π/ × [/Major/ /axis/]^2 or the inverse of
> /Aspect Ratio/. Uses the heading *Round*.
>
>
https://imagej.nih.gov/ij/docs/guide/146-30.html> <
https://imagej.nih.gov/ij/docs/guide/146-30.html>
>
> I think that the 4 in the Roundness definition is not correct,
> and it should be Area/[pi*(Major Axis)^2],
> and not 4 x Area /[pi*(Major Axis)^2]
>
> Am I correct?
>
> --aryeh
>
> --
> Aryeh Weiss
> Faculty of Engineering
> Bar Ilan University
> Ramat Gan 52900 Israel
>
> Ph: 972-3-5317638 <tel:972-3-5317638>
> FAX: 972-3-7384051 <tel:972-3-7384051>
>
>
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>