Posted by
Joel Sheffield on
Oct 30, 2008; 5:11pm
URL: http://imagej.273.s1.nabble.com/Thresholding-help-tp3694620p3694621.html
Justin,
Actually, you have two problems. The first is the uneven
illumination. You can remove this quite easily by using the FFT
bandwidth filter (process, FFT, bandwidth). If you assume that the
gradient of illumination is a large period wave function, then you
can choose a relatively large number for the upper bandwidth and set
the filter not to remove any small details (set the minimum value to
0). I'll send you a copy of the results of this treatment offline.
The more significant problem is that the illumination looks rather
like a DIC or Hoffman image, in which one side of the droplet has
different contrast from the other side. Probably, the only way to
modify this is to change your optics. I doubt that this is possible.
Alternatively, you might work with the Process>Filters>convolve
configurations to flatten the image.
However, it occurs to me that you can set a threshold that will
select the arcs of each droplet and then use the "Analyze Particles"
routine to count the particles and measure the Perimeter of the arcs.
Depending on the degree of accuracy you need, these perimeters would
be in proportion (although I don't know the exact relationship) to
the size of the droplets. It might be sufficient. Again, I'll send
you the data offline.
Joel
> I have a series of images of liquid droplets, which have very poor
> contrast with the surrounding phase, due to the similarities in their
> index of refraction. I get enough contrast in my images to clearly see
> the droplets, however, I can't pick them out with the threshold because
> there is a slight gradient in the brightness of my lighting. Link to a
> sample image is below:
>
>
http://www.chejrw.com/forum/test.tif>
> Does anyone know of a way I can manipulate this image to be able to use
> the 'measure particles' plugin to get the droplet sizes? I can clearly
> see the droplets, so surely there must be a way to make the computer see
> them.
>
> Thanks everybody
>
> - Justin Walker
--
Joel B. Sheffield, Ph.D.
Biology Department, Temple University
1900 North 12th Street
Philadelphia, PA 19122
[hidden email]
(215) 204 8839, fax (215) 204 0486
http://astro.temple.edu/~jbs