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Groups > comp.soft-sys.math.mathematica > #1687

Re: x y coordinates of image pixels for an image outline

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On Apr 12, 5:52 am, william parr <willpower...@hotmail.com> wrote:
> Dear Mathgroup,
>
> I think this problem is fairly straight forward, but I'm struggling with it!
>
> essentially, I want to;
> 1) determine/assign x y coordinate values to the black pixels in a binarised image.
> 2) select the outline black pixels (and get their x y coordinates) on each line of the image.
>
> This falls within a larger project of wanting to recover the outside outline (ie surface outline with x y coordinates) of a bone from a CT slice image. I would then probably aim to create a 3D point cloud for the external bone surface by assigning each slice a z coordinate value. However, unless anyone has a very clever (ie not processor intensive) way of of creating a polygon mesh from the 3D point cloud, I will probably export the point cloud for surface meshing in another program.
>
> thanks in advance,
>
> Will

Will,
  Not too long ago I was trying to do the same thing with an image,
though for a different purpose. What I did was use
MorphologicalComponents[] on the binarized image, which returns
another image with white pixels on the boundary of the object in the
image. I then used Position[ImageData[%],1]  to find the pixel
coordinates of all the white pixels in that image. Then a simple
coordinate transformation can be applied to this list to arrive at the
correct points in x-y. Then like you said, I'm sure you could add a z
coordinate based on the order of the images.

Binarize[pic];
MorphologicalComponents[%];
Position[ImageData[%],1];
points = Map[myCoordinateTransform,%];

-Stefan

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x y coordinates of image pixels for an image outline william parr <willpowers69@hotmail.com> - 2011-04-12 09:52 +0000
  Re: x y coordinates of image pixels for an image outline Stefan <wutchamacallit27@gmail.com> - 2011-04-15 07:56 +0000
    Re: x y coordinates of image pixels for an image outline Stefan <wutchamacallit27@gmail.com> - 2011-04-16 11:33 +0000

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