ImagePro>Re: skeletonisation and object definition

["Kevin Ryan" <kevin[at]mediacy.com>]

If the objects are closed loops, then you will get contiguous skeletons out
of them. If they are not, then pruning will remove them.

Make certain that they are closed - you might try a morphological 'Close' on
them first to close small breaks in the objects.

For example: Sobel on the 'Spots.tif' image, then thin at 50% and prune: you
will lose some objects. Sobel on the 'Spots.tif' image, 5x5 close operator
(which is a 5x5 Max on grayscale images), then thin at 50% and prune: you
will keep all objects.

-- Kevin Ryan
kevin@mediacy.com
Sr. Project Manager

> -----Original Message-----
> From: Image-Pro Plus Users Email List
> [mailto:imagepro-users@lists.mediacy.com]On Behalf Of Glenn Weigel
> Sent: Monday, November 19, 2001 1:11 PM
> To: Image-Pro Plus Users Email List
> Subject: ImagePro>Re: skeletonisation and object definition
>
>
> Thanks very much for the help, Kevin.
>
> With respect to your suggestions on skeletonisation, is there
> also some way
> of ensuring that the thinning process yields a contiguous skeleton (given
> we're starting with a closed-loop object)? I seem to mostly end up with a
> series of non-contiguous line segments - which don't survive
> pruning as you
> pointed out.
>
> Thanks again,
>
> Glenn
>
> Pulp and Paper Research Institute of Canada
> 3800 Wesbrook Mall
> Vancouver, British Columbia
> V6S 2L9
>
> (604) 222-3200
>
>"Kevin Ryan" <kevin@mediacy.com>
>To: <imagepro-users@lists.mediacy.com> (Image-Pro Plus Users Email List)
>Sent by: <imagepro-users@lists.mediacy.com>
>Subject: ImagePro>Re: skeletonisation and object definition
>
> Some excellent questions here; I hope I can help out a bit.
>
> The various branches on your washer represent small deviations along the
> edges of your washer. The thinning filter will represent a single pixel
> 'bump' along the edge of an object with a branch running to that bump as a
> skeleton support.
>
> To minimize this you can perform an opening or a closing on the binary
> object image prior to thinning. This will greatly smooth the outline and
> remove a lot of the branches.
>
> Once you have thinned your object (assuming that it is a closed loop of
> some
> sort) you can prune the skeleton to remove the little branches. Note that
> this does not work for linear objects! If your thinned object is a line,
> rather than a loop, pruning may remove it entirely. Optionally,
> you can use
> the 'reduce' filter, which is a pruning filter that leaves single point
> objects.
>
>
> To segment on edges rather than on intensities:
>
> - Create a secondary image that is an edge filtered version of your
> original. For example, duplicate your image and perform a Sobel filter on
> it.
> - Segment on the edges.
> - Save the outline to a temporary file.
> - Load the outline on your original image to apply edge filtered
> thresholding to the original.
>
> I do this kind of segmentation all the time based on derived images: edges
> (Sobel, Laplacian), textures (variance, median), etc. It's a very useful
> generalized technique.
>
> -- Kevin Ryan
> kevin@mediacy.com
> Sr. Project Manager



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