Re: Measurement of Feret diameter

Posted by Geology Guy on
URL: http://imagej.273.s1.nabble.com/Measurement-of-Feret-diameter-tp5003818p5003982.html

Hi,

>your sample image shows streaks -- probably scratches due to cutting or polishing. You should try to >avoid them by better sample preparation.  If this is not possible, as a second-best option, before >thresholding, you need to remove them.  Do a Fourier transform (FFT), then select the bright wedge with >the polygon tool (the selection should be slightly wider than the wedge, but not reach the very center of >the image). Doing the selection on one side of the center is enough (ImageJ internally uses mirroring). >Then, Process>Math>Set to 0 and do an inverse FFT.  This won't remove the streaks completely, but it >will help a lot.

>Due to noise, you will probably also need some edge-preserving blur plugin such as 'Thresholded blur'.

>Finally, after thresholding and converting to an 8-bit mask:
>As it seems some particles touch each other, you need Process>Binary>Watershed to fully separate the >touching particles.

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>Coming back to your question: the area of an ellipse with major axis 'a' and minor axis 'b' is a*b*pi/4.
>[you will also often fine the equation a*b*pi; then a and b are semimajor and semiminor axes; ImageJ >gives you the full axes, not the half (semi) axes]

>As your particles are solid, there is not much point using the ellipse to measure the area; the 'Area' column >of 'Analyze Particles' gives a more accurate result.


Michael

Thank you very much Michael for your reply and I find your suggestions very helpful.