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Re: Image analysis and ring identification [message #30281 is a reply to message #30277]

Wed, 17 April 2002 21:21

Rachel Pepper
Messages: 3
Registered: April 2002

Junior Member

Actually, the rings often have a bright spot that is not in the center of
the ring, so I don't think the centroiding technique will work. Do you have
any other suggestions?

Thanks,
Rachel

David Fanning wrote:

> 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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