[R] Calculating diameters of cirkels in a picture.

[Bio7]

Hello Bart!

I took your picture and analysed it with ImageJ.
You can do a particle analysis with the image which measures the required
diameter.

I used the "Find Edges" method Process->Find Edges and then adjusted the
Brightness/Contrast/maximum
Image->Adjust->Brightness/Contrast.

After this i converted the image to 8-bit Image->Type->8-bit and thresholded
the image 
Image->Adjust->Threshold until i've got closed circles in red.

In the Analyse->Set Scale and Analyse->Set Measurements dialog I selected
the attributes to measure (Ferrets Diameter or Bounding Rectangle! You have
to adjust the appropriate
scale!).


I then did a particle analysis which excluded particles < 1000
Analyse->Analyse Particles.

If you select the option "Add to Manager" all measured Particles are added
to a "Region of Interest
Manager" ROI in which you can select and measure your Particles seperately,
if you wish.

You can also fit a Ellipse to the selected Particle in Edit->Selection->Fit
Ellipse and then measure
the Particle.

If you want to see a Particle measurement in Action see my application which
uses ImageJ and R and the 
Flash tutorial in which i demonstrate a Particle measurement which is analog
to the ImageJ application.
http://www.uni-bielefeld.de/biologie/Oekosystembiologie/bio7app/flashindex/index.html
http://www.uni-bielefeld.de/biologie/Oekosystembiologie/bio7app/flashindex/index.html 

I highly recommend you to use a new version of ImageJ because of this
capabilities, downloadable at

http://rsb.info.nih.gov/ij/ http://rsb.info.nih.gov/ij/ 

I hope this information is a help for you.

With kind regards

Marcel
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