Re: curvature along the outline of a thresholded object

Posted by foxtango on Jul 12, 2020; 4:20pm
URL: http://imagej.273.s1.nabble.com/curvature-along-the-outline-of-a-thresholded-object-tp5023589p5023688.html

Hi herbie,

I understand your wish to tackle a rigorously posed mathematical problem.
Here are two suggestions.
1) find the curvatures along the outline of a binary object in a wavelength
range given in fractions of the length of the outline.
The second goes back to what you may have meant in your first answer in
this thread.
2) calculate the minimum number of Fourier Descriptors necessary to match
the shape in such a way that the sum of the pixels outside the Fourier
outline plus the white pixels inside the Fourier outline is below a
threshold given in fractions of the area of the object.

Of course, heuristic or experience however named enters in the choice of
the Parameters and where the thresholds are set.

Best, Thomas

Am Sa., 11. Juli 2020 um 19:24 Uhr schrieb Fabrice Senger <
[hidden email]>:

> Ha ha yes if you don't want to run into infinity
>
> Le sam. 11 juil. 2020 à 19:12, Robert Dougherty <[hidden email]> a écrit
> :
>
> > Fabrice,I’m taking a different approach from Herbie and Thomas. For each
> > point, I define the radius of curvature using a circle containing that
> > point and two other points in the polygon. (Actually I apply 3-point
> > smoothing to the pixel polygon from "Wand" to produce the source data.)
> The
> > trick is to choose which other two points.  If the object is supposed to
> be
> > a circle, then the best points for accuracy are far away, not close!  If
> > the shape is more complicated than a circle, then the points have to be
> > closer together, but if they are too close, then the result is noisy.
> I'm
> > still working on the selection algorithm.  I just had an aha moment that
> > the points must not bridge inflection points. This is not yet implemented
> > in my posted code, version 5. I expect it will be in version 6.
> > Bob
> >
> >
> > Sent from Smallbiz Yahoo Mail for iPhonet
> >
> >
> > On Saturday, July 11, 2020, 4:27 AM, Fabrice Senger <
> > [hidden email]> wrote:
> >
> > Dear all,
> > I really enjoyed this thread. I'm right in the assumption that in the end
> > to get the curvature you're sampling the contour with a number of points
> > and use 3 consecutive points to retrieve the radius of curvature? If, so,
> > how do you set the distance between those points, as for small values you
> > will run into noise...
> >
> > Le sam. 11 juil. 2020 à 08:02, Robert Dougherty <[hidden email]> a
> écrit
> > :
> >
> > >  Thomas,
> > > I have updated the plugin at http://www.optinav.info/Curvature.htm.
> > > Version 5 shows tabular output and is probably more accurate than my
> > > earlier version.
> > >
> > > Bob
> > >
> > >
> > >
> > >
> > >    On Sunday, July 5, 2020, 10:14:07 AM PDT, Thomas Fischer <
> > > [hidden email]> wrote:
> > >
> > >  Dear Bob,
> > >
> > > My reply is late because I had computer problems. The result of the
> > plugin
> > > looks nice. In order to use it I would need two features
> > > 1) A parameter to tune the sensitivity. Right now it is not sensitive
> > > enough for my purpose. I am aware that an increase in sensitivity would
> > > make the result more noisy. But as with the plugin of Thomas I would do
> > the
> > > smoothing afterwards.
> > > 2) A list of the curvature values along the circumference. Just looking
> > at
> > > the nice result is not enough in my case. I have to extract numbers
> from
> > > this list.
> > >
> > > I am content with the plugin of Thomas. But as we say in German: the
> > better
> > > is the enemy of the good.
> > >
> > > Best regards, Thomas
> > >
> > >
> > >
> > >
> > >
> > > Am So., 5. Juli 2020 um 07:33 Uhr schrieb Robert Dougherty <
> > > [hidden email]
> > > >:
> > >
> > > >  Gabriel,
> > > > Thanks.  In case it matters, there is a new version with smoother
> > > > calculation and a black background.
> > > > Bob
> > > >
> > > >    On Saturday, July 4, 2020, 11:33:56 AM PDT, Gabriel Landini <
> > > > [hidden email]> wrote:
> > > >
> > > >  Thanks Bob, I can confirm that it works fine.
> > > > I think colourblind observers (red-green type) would see the green as
> > > some
> > > > shades of yellow and blue as blue. At lease that is what the
> Dichromacy
> > > > plugin
> > > > shows.
> > > > Regards
> > > >
> > > > Gabriel
> > > >
> > > >
> > > > On Saturday, 4 July 2020 18:05:09 BST you wrote:
> > > > >  Gabriel,
> > > > > In the meantime, I tried and failed to track down how ImageJ is
> > > supposed
> > > > to
> > > > > load the Phase LUT. Giving up, I changed the code to use another
> > > > > sign-friendly LUT that I coded explicitly.  Now Curvature displays
> > the
> > > > > results in green-blue. Going forward, it may be a question of which
> > > color
> > > > > scheme is better.  One could experiment by running the new version
> of
> > > > > Curvature and then manually changing the LUT to Phase to simulate
> the
> > > old
> > > > > version.  Perhaps green-blue is better for colorblindness than the
> > > > red-blue
> > > > > scheme of Phase?
> > > > >
> > > > > Bob
> > > >
> > > > --
> > > > ImageJ mailing list: http://imagej.nih.gov/ij/list.html
> > > >
> > > >
> > > > --
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> > > >
> > >
> > > --
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> > >
> > >
> > > --
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> > >
> >
> > --
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> >
> >
> >
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> >
>
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