Measurement a siemens star

[dipr]

Hi all,

I'm looking for a tool / plugin / code to measure a "siemens star"
e.g.

I've already searched for a valid solution approach but without success.

Yesterday I've tried to determine the "ellipsis" (in the middle) by calculating the 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

[Herbie-3]

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
>
>
>
>
> --
> View this message in context: http://imagej.1557.x6.nabble.com/Measurement-a-siemens-star-tp5007399.html
> Sent from the ImageJ mailing list archive at Nabble.com.
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html

[dipr]

Herbie,
sorry for the confusion and the late response - indeed, I'm looking for the cut-off frequency.

I've done some testing in Photoshop (multiple rotations with different tonal values per layer). With these images I've repeated the steps I've done before and got some useful results concerning the cut-off frequency.

One problem still exists: How I can determine the spoke target of the siemens star using ImageJ?
Unfortunately I'm no math genius.

Martin