[Matplotlib-users] Plotting boundaries of segmented data

Thomas Caswell tcaswell at gmail.com
Sat Jan 28 14:38:48 EST 2017

You might also be interested in
http://scikit-image.org/docs/dev/auto_examples/edges/plot_contours.html which
may be more efficient at finding the edge.


On Sat, Jan 28, 2017 at 2:36 PM Peter Leitner <peter.leitner at uni-graz.at>

> Indeed, plotting a single contour of binary data is an option I have not
> considered yet. Thank you for the suggestion! For the time being I solved
> the issue by looping through the arrays marking only boundary cells and
> displaying the boundary as a scatter plot which worked quite well, but I
> will revisit your suggestion to effortlessly display the boundary as a
> contour. Many thanks again!
> Peter
> On 01/28/2017 05:45 PM, Thomas Caswell wrote:
> Please subscribe to the mailing list so you can post un-moderated (
> https://mail.python.org/mailman/listinfo/matplotlib-users )
> I think you are looking for the contour family of methods, see
> http://matplotlib.org/examples/pylab_examples/contour_demo.html
> Tom
> On Sat, Jan 28, 2017 at 10:58 AM rwleo <peter.leitner at uni-graz.at> wrote:
> Hello,
> I am trying to plot a 2-D array with segmentation data from a fluid flow.
> The data structure is continuous which means that the segments are
> connected
> regions, like in the picture below:
> <http://matplotlib.1069221.n5.nabble.com/file/n47655/figure.png>
> I use
> plt.imshow(seg, cmap="Greys")
> which returns a black area on a white background. What I would like to
> achieve instead is to plot only the boundary as a black curve, like when
> plotting a shape with pylab setting edgecolor=black and facecolor=white.
> Unfortunately, having the data in matrix format I am not sure whether this
> can easily be achieved without writing a separate function that detects
> whether a pixel belongs to the border or the interior. Is there an
> alternative to the imshow function which does this simply by setting some
> keywords?
> Secondly I would like to smoothen the boundary curve which looks quite
> "rectangular" due to the coarse segmentation algorithm that has been
> applied
> to the fluid flow data. Can this be done with interp2d, if the segments are
> not based on an analytical expression?
> Many thanks in advance!
> --
> View this message in context:
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> --
> Dr. Peter Leitner
> Institute of Physics, University of Graz
> Universitätsplatz 5, 8010 Graz Austria
> Mobile: +43-316-699-17-115-726
> Skype: live:p.leitner_7
> Mail: peter.leitner at alumni.uni-graz.at
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