Posted by
Michael Schmid on
Mar 29, 2016; 5:18pm
URL: http://imagej.273.s1.nabble.com/Getting-started-with-grain-size-analysis-tp5016013p5016024.html
Hi Vaclav,
in my view, you definitely need to improve the illumination.
Use diffuse light from all around, without specular reflections (maybe
the LED ring is too small). Also the camera should have a rather large
focal length, so the viewing direction is the same everywhere.
Then maybe try something along these lines:
- 'Subtract background' with small radius (≈3) and 'Sliding Paraboloid'
to get the outlines
- Threshold to get the outlines without breaks (best find a suitable
AutoThreshold method, so it does not depend too much on brightness)
- Skeletonize
- Erode with count=7 and many iterations (≈30) in the Binary Options to
get rid of the short line segments
- Smooth
- Threshold to get lines as background, and the lines thicker than 1 pxl
where they run diagonally (fixed threshold values, no AutoThreshold here)
- Analyze Particles with a rather high minimum circularity (try values
around 0.5-0.8), to avoid getting partially visible beads in the
background. Use one of the 'Show' options to see whether the result is
satisfactory.
It won't be perfectly quantitative, but it will provide an indication if
the grain size changes.
Best wishes,
Michael
________________________________________________________________
On 2016-03-29 14:44, Václav Šmilauer wrote:
> Hi Gabriel, thanks for suggestions.
>> The image you posted has too many issues and I doubt that you would be
>> able
>> the analysis you want accurately without redesigning your setup.
>>
>> The first problem is the overlapping. You would do much better if your
>> particles were on a single layer on a contrasted background. maybe you
>> can get
>> some surface with wells where each grain sits in one of those.That
>> would also
>> help with identifying the individual objects.
> That is true, and I am aware that the current setup does not simplify
> things. Unfortunately it is bulk material on conveyor with the flow in
> the order of 100t/h. I will see what could be done.
>> You should aim to reduce the uneven illumination. I would suggest that
>> you try
>> to resolve this issue before image capture, as doing it
>> programatically tends
>> to create new artefacts. Have you tried a light diffuser? or several
>> light
>> sources?
> The light is ring-shaped LED strobe already diffused with
> hemisphe-shaped matte white reflector/diffuser (thus all the light is
> reflected). Will try larger diameter of the diffuser, this one is just
> about 10cm.
>> Also note that JPEG images are not good for imaging. They are lossy
>> compressed, which add image artefacts which further interfere with the
>> subsequent processing. Better save your data in TIFF or PNG formats.
>> Saving a
>> JPEG to TIFF to PNG does not resolve anything as the artifacts are
>> already
>> there.
> It must have been imgur which serves the image as JPEG, normally it is
> obtained uncompressed from GigE camera and stored as PNG.
>
> Cheers, Vaclav
>
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