[Matplotlib-users] Plotting boundaries of segmented data

Thomas Caswell tcaswell at gmail.com
Sat Jan 28 11:45:11 EST 2017

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I think you are looking for the contour family of methods, see


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!
> --
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