Re: Questions about equations of Shape Descriptors
Posted by
Gabriel Landini on
Feb 25, 2010; 10:34pm
URL: http://imagej.273.s1.nabble.com/Questions-about-equations-of-Shape-Descriptors-tp3688338p3688339.html
On Thursday 25 February 2010 21:10:46 you wrote:
>
http://rsbweb.nih.gov/ij/docs/menus/analyze.html says:
>
> *Round* (roundness): 4*area/(π*sqr(major axis)), or the inverse of the
> aspect ratio.
>
> So... does area in this equation mean "area of best fit ellipse" ?
No, it is area of the blob, which in IJ is the number of pixels.
Note that other plugins (such as the particles8 and 4 plugins) compute area
differently than IJ, and so the result values might not be exactly the same.
> suppose it does, as we're talking about "major axis" in the denominator.
Major axis, here means "maximum Feret diameter" of the blob.
> Also, does sqr mean pow(major axis, 2) aka (major axis)^2 ?
> In that case, how'd you write square root?
pow (n, 2) is n^2.
sqrt(n) is the square root of n, see the macro functions.
G.