Re: Measurement a siemens star

Posted by Herbie-3 on Apr 23, 2014; 9:52am
URL: http://imagej.273.s1.nabble.com/Measurement-a-siemens-star-tp5007399p5007400.html

Martin,

to "measure" a spoke target can mean a lot...

I guess you are interested in the "cut-off" frequency which isn't always
well-defined.

One way of tackling this problem is by analyzing the gray value of
spokes along properly inclined straight lines. Another way is to analyze
the local contrast of the pattern.
I'm not aware of any IJ-plugins that are directly devoted to such analyses.

Another approach -- that I would follow -- is to look at the Fourier
power spectrum of the spoke target and evaluate the spectral decline at
high spatial frequencies. Of course, before performing the FT you must
properly window the spoke target.

Just some thoughts

Herbie

::::::::::::::::::::::::::::::
On 23.04.14 08:53, dipr wrote:

> Hi all,
>
> I'm looking for a tool / plugin / code to measure a "siemens star"
> e.g.
> <http://imagej.1557.x6.nabble.com/file/n5007399/siemensstar.png>
> I've already searched for a valid solution approach but without success.
> Yesterday I've tried to determine the "ellipsis" (in the middle) by
> calculatingthe mean tonal values per row / col, but the results weren't very
> convincing as well.
> At best, the solution is d(min) and d(max) which describes the ellipsis in
> the center of the siemens star.
> Do you know any approach / solution?
> Thanks!
> Regards,
> Martin
>
>
>
>
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