Posted by
Gabriel Landini on
Nov 27, 2005; 10:32am
URL: http://imagej.273.s1.nabble.com/particle-analysis-Feret-diameter-tp3704371p3704378.html
On Sunday 27 November 2005 08:57, K. Kachrimanis wrote:
> If this is the maximum Feret and it is selected from all Ferets measured,
> then the only thing missing is to report the minimum and a mean Feret also.
My plugin Particles8_Plus at
http://www.dentistry.bham.ac.uk/landinig/software/software.htmldoes most of the descriptors mentioned and includes the angle of the maximum
feret diameter. It also calculates the Breadth, which I think is a better
parameter than the minimum feret, but it uses a different way to estimate
perimeter (it uses Freeman's algorithm) so sometimes the results are not
exactly the same as the built-in analyser.
How do you propose to place the other feret diameters at n angles?
Is this based on the image frame of reference or angles offset from the
direction of the largest one?
And what should one use, the centroid or the centre of mass of the particle?
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.
> a "microshape" descriptor is also available (fractal dimension),
Fractal dimension is not a microshape descriptor, but a global one which has
no scale (and therefore is not micro, meso or macro). However I have been
always suspicious of other commercial programs that "estimate" the f dim of
particles, for two reasons:
1."particles" I guess are image objects that are most of the time not large
enough to satisfy the requirement of an order of magnitude in the range of
scales analysed.
2. fractal dimension is a bit of a statistical measure, it depends of a
goodness of fit to a particular model, so the "goodness" of the result needs
to be monitored by some other means (for instance the r-squared of a log-log
plot linear fit). When particles are all different sizes, these goodness of
fit are not comparable (it is not the same to look at a 30 pixel particle
than to a 30000 pixel one, in the latter there will be much larger scales
that are not present in the former, and so one is not measuring the same
property unless we already know that the objects are strictly fractal). I do
not think that it is a good idea to do this blindly.
I think that if f dim is incorporated in the Particle Analyzer, it is going to
be misused extensively. If there were a vote I would go for "no".
Cheers,
Gabriel