Posted by
robert atwood on
Mar 29, 2016; 11:29am
URL: http://imagej.273.s1.nabble.com/Getting-started-with-grain-size-analysis-tp5016013p5016018.html
Dear
Could the focal depth-of-field be made smaller such that the edges of particle that are in the layer below are out of focus -- so only the edges of the top particles are in focus?
Uneven illumination looks like it should be so easy , since the brain has great 'algorithms' for interpreting it -- yet is so much of a problem to deal with. As Gabriel already suggested, any improvement in the set-up to reduce this would help much more than algorithms.
However, if in the end there is some impossible to remove un-evenness, I have used --
-- Fourier filter high pass method (Imagej FFT 'bandwith' filter , with something like 'small features = 3 , large features=100 ' or play around , depends on the total pixel-size of the image and size of particles,
-- Successive blurring and subtraction e.g use Mean or Gaussian blur filter with largest kernel , repeating a few times, then subtract this from the original,
-- ImageJ has a 'rolling ball' called 'remove background' with several options.
-- This article:
http://hdl.handle.net/10380/3133 describes implementation of applying Otsu's threshold to uneven image by applying to a set of small neighbourhoods and then splining the respective background levels.
But, as Gabriel suggests, I think none of these will work very well for your case, without some initial improvement of the extreme degree of unevenness. The upper-right particles appear to saturate the intensity.
Good luck
Robert
> -----Original Message-----
> From: ImageJ Interest Group [mailto:
[hidden email]] On Behalf Of
> Gabriel Landini
> Sent: 28 March 2016 10:44
> To:
[hidden email]
> Subject: Re: Getting started with grain size analysis -
>
> On Sunday 27 Mar 2016 20:14:53 you wrote:
> > I am new to the list and have close to no experience with ImageJ (or
> > image analysis) but have a solid background in physics and programming.
> > I am facing the task of determining grain size distribution in photos
> > from industrial camera. A typical image is like this:
> >
http://i.imgur.com/lwuOBeh.jpg (the diagonal separates two types of
> > material which has different reflecitivity). The eventual goal is an
> > unattended analysis under controlled conditions (same lighting,
> > resolution etc). I have some issues getting a reasonable result with
> > ImageJ and I would appreciate some help on how to move forward. Could
> > someone suggest a way I could try?
>
> 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.
>
> 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?
>
> 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.
>
> Hope this helps
> Gabriel
>
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