Posted by
karo03 on
Jan 27, 2009; 1:20pm
URL: http://imagej.273.s1.nabble.com/Possible-bug-with-perimeter-calculation-on-composite-selections-tp3693924p3693927.html
Interesting discussion.
What I still miss in this thread is the discussion about the objects
under examination, their variability and overall shape and the
necessity.
The problem with perimeter occured with groups of disconnected objects
considered as one object. In this case I think the perimeter is mostly
useless except the size of the isolated connected objects varies only
similar or equal to the other object members.
As a recommendation: I would start with simple measures: Area,
Extension (max object extension (box)), minimal inscribable circle
(max distance of object). If these are not discriminative enough,
further, more complicated measures have to be tested, eg P^2/A (to
avoid size (and pixel scaling) effects) ...
The problem with perimeter of groups of objects is manifest. If the
perimeter is really necessary there are ways to circumvent the actual
calculation with other means, eg with the morphology library of Gabriel.
Regards
Karsten
Am 27.01.2009 um 11:51 schrieb Gabriel Landini:
> On Tuesday 27 January 2009 04:28:17 Chris Bradhurst wrote:
>> As far as whether perimeter will actually have any discriminating
>> value
>> remains to be seen, although I suspect it will likely be
>> ineffective, in
>> accord with your experience.
>
> What Kenneth was talking about is a special type of geometrical
> object where
> the perimeter length scales with observational scale (i.e. fractal and
> asymptotic fractal boundaries).
> Those are very common in nature and so comparing their perimeters is
> only good
> for a single resolution (while is unlikely to be exactly the same
> across
> different setups).
> Many traditional shape descriptors use also the perimeter in the
> calculation
> (like circularity, shape factor, etc) so those can be badly affected
> as well.
>
> For complex/fractal particles with varying sizes, computing their
> fractal
> dimension is much more robust and informative than other shape
> parameters.
>
> The paper full reference is very much worth reading:
>
> Mandelbrot B. How long is the coast of Britain? Statistical self-
> similarity
> and fractional dimension. Science 1967;156:636-638.
>
> And within the biological context everybody doing microscopy should
> read these
> two (both way ahead of their time):
>
> Paumgartner D, Losa G, Weibel ER. Resolution effect on the
> stereological
> estimation of surface and volume and its interpretation in terms of
> fractal
> dimensions. Journal of Microscopy 1981;121(1):51-63.
>
> Rigaut JP. An empirical formulation relating boundary lengths to
> resolution in
> specimens showing 'non-ideally fractal' dimensions. Journal of
> Microscopy
> 1984;133(1):41-54.
>
> Cheers
>
> Gabriel
Karsten
[hidden email]