Posted by
Gabriel Landini on
Dec 12, 2016; 7:24pm
URL: http://imagej.273.s1.nabble.com/Ever-decreasing-circles-tp5017755p5017766.html
On Monday, 12 December 2016 14:37:32 GMT John M Brear wrote:
> Attached is a typical image - converted to 8-bit. You can see that several
> types, sizes and spatial distributions of particles are present.
[...]
> To be explicit, particle 37 has an area of 1 and a perimeter of 2.828,
> giving a calculated circularity of 1.5713 - whereas a value of 1 is
> reported.
I had a look at your image. You get that result because particle 37 is just 1
pixel. The error for perimeter estimation is the largest for that case.
That is why the Documentation warns that for small regions the values are not
reliable and outputs 1 instead.
> Whether or not these calculated circularities are strongly meaningful is
> beside the point. Practically they are calculable and show a trend with
> interesting features that may betoken something of real interest, or serve
> to highlight a processing artifact.
> All I wish to do is select my set for analysis in a manner that allows
> choice of circularity values >1.
I do not think this is robust or a good idea, but... the way to do what you
are after is to read all the areas and perimeters from the table, then
generate a new column in the Results table then do with that value the
analysis you are after.
The following code will generate a new circularity column with the values you
want if you run it just after Analyze Particles:
for (i=0; i<nResults; i++) {
setResult('MyCirc', i, (4.0* PI * getResult("Area", i)) /
(getResult("Perim.", i) * getResult("Perim.", i)));
}
Cheers
Gabriel
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