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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg118171] Re: x y coordinates of image pixels for an image outline
  • From: Stefan <wutchamacallit27 at gmail.com>
  • Date: Fri, 15 Apr 2011 03:56:21 -0400 (EDT)
  • References: <io17cv$i44$1@smc.vnet.net>

On Apr 12, 5:52 am, william parr <willpower... at 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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