Posted by
Gabriel Landini on
Nov 27, 2005; 4:42pm
URL: http://imagej.273.s1.nabble.com/particle-analysis-Feret-diameter-tp3704371p3704380.html
Hi Philippe,
On Sun, 27 Nov 2005, Philippe Grosjean wrote:
> Gabriel Landini wrote:
> No, you just calculate Feret diameter for each angle. You have a vector
> of Feret diameters.
Ok, the confusion comes from how I have implemented it (and I wonder if IJ
uses a similar method, I have not checked). I have followed what other
imaging programs seem to do too (Nexus and I think Optimas too): to detect
the furthest 2 points along the convex hull. Of course this does
not guarantee that this line pases through the centre of mass.
This longest distance does not depend of the orientation of the particle
because the way it is calculated.
> Maximum is the max value in this vector. Minimum is
> min value. Mean is the average of all values. This is how Matrox Imaging
> Library calculates the three values. According to MIL, breadth is max
> Feret/min Feret. So, no mather if you have max and min Feret or max
> feret and Breadth... you can calculate the third parameter easily. May
> be do you calculate breadth in a different way?
I use "breadth" as the shortest distance orthogonal to the longest
diameter (as defined above). This distance is not necessarily on the same
line on both sides of the longest diameter. (a macro is included in the
morphology.zip that draws this.
> > Note that when using the centre of mass, holes in the particle make it
> > difficult to standardise the measurements (the same particle filled and with
> > holes has different feret legths because the "centre" is in a different
> > location.
>
> Sorry, but I don't understand how this affects calculation of Feret
> diameter. Obviously, choosing a different centre for rotation affects
> the way the rotated particle is represented (well, just a translation
> depending on the choosen centre). However, as far as I know, Feret
> diameter is not constrained to pass by a given centre. So, no mather
> which centre you use for the rotation, once your particle is rotated,
> you should get the same Feret diameter. This is true also for holes:
> Feret is calculated on the outline of the particle. So, holes have no
> effect on it.
Hmm... I am confused how the algorithm should work. Can you give an
example (just a description)on how is the whole set of Feret diameters
calculated?
Cheers,
Gabriel