| Image analysis and ring identification [message #30311] |
Wed, 17 April 2002 06:55  |
Rachel Pepper
Messages: 3
Registered: April 2002
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Junior Member |
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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!
Rachel
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| Re: Image analysis and ring identification [message #30343 is a reply to message #30311] |
Fri, 19 April 2002 00:14  |
Karsten Rodenacker
Messages: 98
Registered: July 1997
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Member |
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Without proposing completly ready written routines. Maybe you do:
1. Contour with path_xy on you (binary) image. You get pathes for the
outer and inner border (thers is a flag in path_info)
2. Take the outer border path say xy from one 'ring' and calculate a
normalized contour path, by:
nxy=fft_norcur(xy,centr=av,size=sz,perim=p)
as far as I remind me in av you will find the centroid coordinates, in
sz the radius and in p the perimeter.
FUNCTION sh_dist, xy
L = sqrt(sh_diff(reform(xy[0, *]))^2+ $
sh_diff(reform(xy[1, *]))^2)
return,L
end
FUNCTION fft_norcur, xy, CENTROID=cav, FACTOR=av, SIZE=sz, PERIMETER=p
dim=(size(xy))[1]
n=(size(xy))[2]
d=sh_dist(xy)
vd=fltarr(dim,n)
FOR i=0,dim-1 DO vd[i,*]=d
cav=total(xy*vd,2)/total(vd,2)
oxy=xy
oxy[0,*]=reform(xy[0,*])-cav[0]
oxy[1,*]=reform(xy[1,*])-cav[1]
p=total(d)
tt=oxy[0,*]^2+oxy[1,*]^2
sz=sqrt(total(tt))
av=total(sqrt(tt)*d)/p
return,oxy/av
END
Regards
Rachel Pepper wrote:
> 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!
>
> Rachel
>
>
--
Karsten Rodenacker ()
------------------------------------------------------------ -------------:-)
GSF - Forschungszentrum Institute of Biomathematics and Biometry
D-85758 Oberschleissheim Postfach 11 29
Tel: +49 89 31873401 | FAX: ...3369 | rodena@gsf.de |
Karsten@Rodenacker.de
http://www.gsf.de/ibb/homepages/rodenacker
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| Re: Image analysis and ring identification [message #30352 is a reply to message #30311] |
Thu, 18 April 2002 11:47 |
Rachel Pepper
Messages: 3
Registered: April 2002
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Junior Member |
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Sorry to be so confusing! I want the center of the circle (ie the bright ring)
and the bright spots are messing up the centroid-based method (James is right).
Rachel
David Fanning wrote:
> James Kuyper (kuyper@gscmail.gsfc.nasa.gov) writes:
>
>> Yes, but I didn't get the impression that he wants to find the bright
>> spot. He asked how to determine the center of the circle, and complained
>> about the fact that the bright spot would mess up the centroid-based
>> method of calculating the center, because the bright spot was off-center.
>
> Isn't language odd? I thought she asked how to find the
> center of the ring, but then realized she wasn't interested
> in the center, but in the bright spot, which wasn't necessarily
> in the center. I think she might be able to have her cake
> and eat it too, depending upon the values she uses to
> calculate the centroid. In fact, she might even learn
> something fascinating about her rings by measuringg how
> the centroid changes between the two different calculations.
>
> But, hang on a minute! We don't have to be Aristotle and
> his friends arguing endlessly about how many teeth a
> horse has, we can ask the source. Rachel, what in the
> world are you asking about?
>
> Cheers,
>
> 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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| Re: Image analysis and ring identification [message #30462 is a reply to message #30352] |
Mon, 22 April 2002 11:56 |
Jonathan Joseph
Messages: 69
Registered: September 1998
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Member |
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How large are these rings that you are talking about?
I have some IDL code that will fit an ellipse to a group of points.
It requires at least 6 input points. The center is readily available.
I hesitate to just post it because it's not my own code.
I found the code on the web written in java and took the bits that
were relevant to me and converted them to IDL. It's publicly
available code - but very few comments, no warranty, etc. I
believe the original author's name is Maurizio Pilu (see
http://vision.dai.ed.ac.uk/maurizp/ElliFitDemo/ for a demo)
If it looks useful, I can post my IDL code.
-Jonathan
Rachel Pepper wrote:
>
> Sorry to be so confusing! I want the center of the circle (ie the bright ring)
> and the bright spots are messing up the centroid-based method (James is right).
>
> Rachel
>
> David Fanning wrote:
>
>> James Kuyper (kuyper@gscmail.gsfc.nasa.gov) writes:
>>
>>> Yes, but I didn't get the impression that he wants to find the bright
>>> spot. He asked how to determine the center of the circle, and complained
>>> about the fact that the bright spot would mess up the centroid-based
>>> method of calculating the center, because the bright spot was off-center.
>>
>> Isn't language odd? I thought she asked how to find the
>> center of the ring, but then realized she wasn't interested
>> in the center, but in the bright spot, which wasn't necessarily
>> in the center. I think she might be able to have her cake
>> and eat it too, depending upon the values she uses to
>> calculate the centroid. In fact, she might even learn
>> something fascinating about her rings by measuringg how
>> the centroid changes between the two different calculations.
>>
>> But, hang on a minute! We don't have to be Aristotle and
>> his friends arguing endlessly about how many teeth a
>> horse has, we can ask the source. Rachel, what in the
>> world are you asking about?
>>
>> Cheers,
>>
>> 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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