Re: Measurement of Feret diameter

Posted by Geology Guy on Jul 12, 2013; 12:51pm
URL: http://imagej.273.s1.nabble.com/Measurement-of-Feret-diameter-tp5003818p5003956.html

On Jul 11, 2013, at 9:29 AM, Michael Schmid wrote:

> Hi everyone,
>
> there was a recent thread on the accuracy of the Feret diameter in ImageJ.
>
> 'Analyze Perticles' does not use the code of shapeRoi but the code in Roi.java.  There, the maximum Feret (and the Feret angle, which refers to the maximum width) is calculated accurately, by a double loop over the corner pixels. Varying the angle (in 0.5-degree steps) is used only for the minimum Feret.  This is quite accurate unless the particles are elongated extremely much. Shape Rois are created only as a result of merging or intersecting rois; this does not happen when using 'Analyze Particles'. Anyhow, if you have objects that can be approximated as circles (2D section through spherical particles or 2D projection of spheres), the area or 'Fit Ellipse' give you much better indications of size than the Feret diameters.  If you want to use the Feret nevertheless, assuming ellipsoidal particles, one would typically use sqrt(minFeret * maxFeret), not the arithmetic mean.
>
> Michael

Thanks Michael for the clarification.