Posted by
Adam Hughes on
Feb 19, 2014; 8:13pm
URL: http://imagej.273.s1.nabble.com/Circularity-error-tp5006583p5006594.html
Michael,
Thanks. I also just thresholded and used the rasterised circles. I've
since tried again in FIJI to ensure the results were the same, and they
are. As Gabriel pointed out, it's unusual that you'd get a circularity of
1 for you smallest particles, no? The small particles are rectangles and
should have the least circularity in principle, although the encoding
method, as Gabrield said, can deviate from the geometric fit of that
particluar object.
Gabriel, thanks for pointing out that you think a correction may be in
place. If anyone knows more about this correction, I'd be interested in
learning a bit about it.
As for the non-corrected values, I would like to try the Particles8 plugin
but can't find a link after a quick search. Will search futher later;
however, since imj outputs the perimiter and area already, wouldn't the
circularity that I've computed from the equation 4pi * A / P**2 be the
non-corrected value? This is shown in my plot as the blue points.
On Wed, Feb 19, 2014 at 2:56 PM, Gabriel Landini <
[hidden email]>wrote:
> 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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