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Re: Need Some Good Ideas [message #29425 is a reply to message #29424]

Thu, 21 February 2002 14:35

Martin Downing
Messages: 136
Registered: September 1998

Senior Member

Hi David,

refering to your gateway blobs:
if thats what you have then they are easy to segment, you then identify each
individual blob using region labeling

now for each blob:
1. identify the boundary (this should be as a [x,y] array of every boundary
pixel (no long sides)- as either an internal or external boundary
2. transform the array to [s,theta], where s[i] is the cumulative distance
along the boundary to P[i] and theta[i] is the angle of the link of P[i-1]
from P[i] relative to (say) the X axis
3. [s,theta] will be periodic,(i.e. you could carry on going round and
round), so you can now run a FFT or calculate the first fourier descriptors
of it - see reference

good luck - I spend rather too much time playing with this kind of stuff!

Martin

Reference List
1. Lin, Chellappa R. Classification Of Partial 2-D Shapes Using Fourier
Descriptors. IEEE Transactions On Pattern Analysis And Machine Intelligence
1987; 9:686-690

--
----------------------------------------
Martin Downing,
Clinical Research Physicist,
Grampian Orthopaedic RSA Research Centre,
Woodend Hospital, Aberdeen, AB15 6LS.
m.downingATabdn.ac.uk

"David Fanning" <david@dfanning.com> wrote in message
news:MPG.16de0d88b1cdeb82989813@news.frii.com...
> Folks,
>
> Do you have your thinking caps on? I'm looking for
> a few good ideas.
>
> I have a bunch of blobs. (Think spots on the
> Gateway cow.) I would like to analyze the curvature
> and bends in the perimeter of the blobs. I have
> the indices of the points that make up the blob, and
> I have obtained the "perimeter" points by contouring
> the blob. Unfortunately, these perimeter points are
> not evenly distributed. (Think of a blob that has a
> long, straight side. The contour command will put a
> point at either end of the straight bit, so the points
> on that side of the blob are sparse, while the points
> along a tight bend on the other side of the blob
> are dense.)
>
> I say "unfortunately" because we have a method that
> uses the derivative of the perimeter at each point
> and the FFT transform of the derivative distribution,
> but it seems to be giving funny results because of this
> point distribution problem.
>
> Has anyone heard of this kind of curvature analysis
> before? Any pointers to literature? I've heard that
> IDL can be used to solve these kinds of problems. :-)
>
> Thanks,
>
> David
> --
> David W. Fanning, Ph.D.
> Fanning Software Consulting
> Phone: 970-221-0438, E-mail: david@dfanning.com
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
> Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Re: Need Some Good Ideas By: btupper on Thu, 21 February 2002 14:35
		Re: Need Some Good Ideas By: Martin Downing on Thu, 21 February 2002 14:35
		Re: Need Some Good Ideas By: David Fanning on Thu, 21 February 2002 11:22
		Re: Need Some Good Ideas By: btupper on Thu, 21 February 2002 10:43
		Re: Need Some Good Ideas By: David Fanning on Thu, 21 February 2002 08:09
		Re: Need Some Good Ideas By: David Fanning on Thu, 21 February 2002 07:50
		Re: Need Some Good Ideas By: dw on Thu, 21 February 2002 07:22
		Re: Need Some Good Ideas By: ronn on Thu, 21 February 2002 04:46
		Re: Need Some Good Ideas By: Craig Markwardt on Wed, 20 February 2002 23:46
		Re: Need Some Good Ideas By: Craig Markwardt on Wed, 20 February 2002 23:02
		Re: Need Some Good Ideas By: Stein Vidar Hagfors H[1] on Fri, 22 February 2002 09:05

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