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Re: Image analysis and ring identification [message #30310 is a reply to message #30281]

Wed, 17 April 2002 07:29

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Rachel Pepper (Rachel_Pepper@brown.edu) writes:

> I am a fairly new IDL user trying to use image analysis to determine
> particle positions in my images. After filtering the images, they
> appear to be bright rings around a dark center. I was wondering if
> anyone knew a routine to fit these sorts of images to a circle so that
> the center of the ring could be determined. Thanks for any help!

If you can isolate the "blobs" (as we usually call them) in
your image (e.g., with Label_Region or with something home-grown)
and obtain the indices of the pixels in the blob, then you can
calculate the centroid of the pixel distribution in the manner
described on this page:

http://www.dfanning.com/tips/centroid.html

Craig Markwardt wrote me a nifty little routine one time
to then fit an ellipse to the pixel distribution in an
attempt to characterize the size, shape, and orientation
of the blobs. I keep meaning to make this algorithm available,
but I haven't gotten around to it yet. (And I don't really
what to cut into Craig's significant income as the Expert's
Expert, if you know what I mean.)

Cheers,

David

P.S. By the way, Craig. I put that check in the mail to
you today. Really! :-)

--
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: Image analysis and ring identification By: James Kuyper on Thu, 18 April 2002 08:07
		Re: Image analysis and ring identification By: Paul Van Delst[1] on Thu, 18 April 2002 06:44
		Re: Image analysis and ring identification By: David Fanning on Thu, 18 April 2002 06:05
		Re: Image analysis and ring identification By: Paul Van Delst[1] on Thu, 18 April 2002 05:37
		Re: Image analysis and ring identification By: Rachel Pepper on Wed, 17 April 2002 21:21
		Re: Image analysis and ring identification By: David Fanning on Wed, 17 April 2002 07:29
		Re: Image analysis and ring identification By: Dan Larson on Thu, 18 April 2002 08:37
		Re: Image analysis and ring identification By: David Fanning on Thu, 18 April 2002 08:33

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