[R] Calculating diameters of cirkels in a picture.

[Moshe Olshansky]

Hi Bart,

I have never used image processing software in R (I
was doing this with Matlab), but here is what I would
have done algorithmically:
1) convert the picture to gray-scale
2) find a threshold value which separates the circles
from the background and convert your image to black
and white
3) if the circles are far apart use morphological
closing to fill in small holes inside the circles (may
be do this several times)
4) use labeling to split the image into connected
components
5) for each connected component get it's area (the
number of pixels) and use the formula S = Pi*R^2 to
find the approximate radii.

Regards,

Moshe.

--- Julian Burgos <jmburgos at u.washington.edu> wrote:

> Hi Bart,
> 
> If you only have 36 circles, the fastest way would
> be to use some image 
> processing software and measure the circles "by
> hand".  One option is to 
> use ImageJ, which you can download here
> 
> http://rsb.info.nih.gov/ij/
> 
> Julian
> 
> Bart Joosen wrote:
> > Hi,
> >
> > Maybe this is more a programming questions than a
> specific R-project question, but maybe there is
> someone who can point me in the right direction.
> >
> > I have a picture of cirkels which I took with a
> digital camera.
> > Now I want to use the diameter of the cirkels on
> the picture for analysis in R.
> > I can use pixmap to import the picture, but how do
> I find the outside cirkels and calculate the
> diameter?
> > I pointed out that I can use the edci package, but
> then I need to preprocess the data to reduce the
> points, otherwise it takes a long time, and my
> computer crashes.
> >
> > If you want to see such a picture, I cropped a
> larger one, and highlighted the cirkel which is of
> interest.
> > In a real world, this is a plate with 36 cirkels,
> which all should be measured.
> > www.users.skynet.be/fa244930/fotos/outlined.jpg
> >
> >
> > Thanks for your time
> >
> > Bart
> > 	[[alternative HTML version deleted]]
> >
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> >
> 
> ______________________________________________
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> and provide commented, minimal, self-contained,
> reproducible code.
>