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Re: Questions about equations of Shape Descriptors

Posted by Michael Cammer-2 on Feb 26, 2010; 7:43pm
URL: http://imagej.273.s1.nabble.com/Questions-about-equations-of-Shape-Descriptors-tp3688338p3688344.html

In the ratio, at times we've also used the perimeter instead of the
Feret's diameter.  I think the rationale was that for very irregular
objects the Feret's doesn't change much while the perimeter could
continue to grow very large.
-Michael C

On Fri, Feb 26, 2010 at 8:01 AM, Norbert Vischer <[hidden email]> wrote:

> Hi Gabriel,
>
> of course I agree with you that Feret is less abstract, and often comes close to what one really wants to know.
> But any noise or other irregularities biases the Feret parameters to be overestimated.
>
> In our lab, we measure rod-shaped bacteria (cylinders with hemispherical caps), and if we would use Min Feret to classify the diameter of the cylinder (13..15 px), a single noise pixel or slightly bent cylinders would lead to large overestimation.
> So we better use the ellipse parameters and convert them with an equation into length and diameter. The converter equation assumes that the image of the rod has the same moments of inertia as the ellipse found by ImageJ.
> For any shape that has two axes of symmetry, and that can be described with two parameters, such a converter equation can possibly be found.
>
> regards, Norbert
>



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