Posted by
Juanjo Vega on
Jun 20, 2011; 12:40pm
URL: http://imagej.273.s1.nabble.com/Area-measurements-for-50-particles-on-one-image-image-attached-tp3684189p3684193.html
Hi,
To get exactly 50 particles you need to perform a perfect segmentation... quite difficult... though, try to remove shadows from your images by providing a better light source. As you can see, there are many shadows on it, and as they are dark, stones close to others might be taken as just one.
You can place a perpendicular light source, or several of them, so lighting will be the same (or at least closer to be the same) for the whole surface, so the background can be thresholded easier at the same time you avoid to take groups of particles as single big ones. For human eye it's clear where the particles are, but computer vision algorithms are not so smart ;)
After that, I'd use some adaptative thresholding method. Have a look to the histogram and you'll see two peaks, if you threshold in the middle of them you'll separate your particles from the backgorund. Some algorithms detect those peaks and threshold at the most convenient value, so small light variations don't affect so much and they work much better than thresholding always at the same value.
For now, just try to improve your images lighting and then we'll see which algorithms work better :)
Sincerelly,
Juanjo.
On Jun 20, 2011, at 12:48 PM, janaka kumara wrote:
> Dear all,
>
> In this image, there are 50 particles. I want to measure areas for each particles but when I do using ImageJ toolbar, I don't get area measurements for all particles (50). I do analyses as follows,
>
> - Analyze, then Set Scale (to set a scale)
> - Rectangle shape selection (to remove ruler on the image)
> - Edit, then clear outside (now only particles remained on the image)
> - Process, then Find Edges
> - Process, then Binary, then Make Binary
> - Process, then Binary, then Dilate (as images are not very clear)
> - Analyze, then Analyze particles, there
> size (mm2): 5-infinity
> circularity: 0-1.00
> show: outlines
>
> Then, on the result sheet, I cannot see data for exactly 50 particles.
>
> Could you please advice me on this matter?
>
> Note: due to limitation for size, image attached was resized. If you want the original image, I can give you it if you will send me your email address.
>
> Thank you.
>
> Yours sincerely,
> Kumara
>
> PhD candidate
> Geotechnical Engineering Laboratory
> Department of Civil Engineering
> Yokohama National University, Japan<gravels - PSD.jpg>
------------------------------------------------------------
Juanjo Vega (
[hidden email])
Unidad de Biocomputación. Laboratorio B-13.
Centro Nacional de Biotecnología. CNB-CSIC.
C\ Darwin, 3. Campus de Cantoblanco.
Universidad Autónoma de Madrid.
28049, Madrid, Spain.
http://www.cnb.csic.eshttp://www.biocomp.cnb.csic.es+34 91 585 4510
"Las mejores almas son capaces de los mayores vicios como de las mayores
virtudes, y aquellos que caminan despacio por el camino recto pueden
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del Método, René Descartes.