Re: Circularity error?

Posted by Gabriel Landini on Feb 19, 2014; 7:56pm
URL: http://imagej.273.s1.nabble.com/Circularity-error-tp5006583p5006593.html

On Wednesday 19 Feb 2014 19:28:19 Cammer, Michael wrote:
> I took your image of circles, thresholded it, and ran particle analyzer on
> it.  The resulting calculated circularity looks different than your results
> (attached).  Did you draw a circular ROI and measure it as opposed to the
> raster based circles?  Regardsless, the Roundness was 1 for all the
> circles.

You can't get circularity of 1 on a square lattice, because you can only
approximate a circle. The error varies with the size of the region (and the
encoding methods used to compute for perimeter and area).
I think the particle analyzer in IJ does (or used to do) some correction for
small size regions. That might be desirable when filtering regions by
circularity.

If you want to get the non-corrected values, the Particles8 plugin computes
those.

Regards

Gabriel

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