Help with 2D planer fit.

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Parag on 17 Oct 2015
Commented: Bjorn Gustavsson on 21 Oct 2015
Hi Guys
I want to filter the low frequency noise in my image without actually manipulating spacial frequecy information so thinking to 2D planer fit the region around my object and subtract from the original image. I have CT image with disk object. Can you please let me know algorithm how to 2D planer fit the region around the object. I have attached image Thank you
Bjorn Gustavsson
Bjorn Gustavsson on 21 Oct 2015
That does not make sense. You can do that to remove the background, but that is somewhat separate from your noise - unless you have some kind of interference-pattern noise in your image the noise is most likely rather randomly varying from pixel to pixel with very small spatial correlation, so the noise in the bright region wouldn't depend directly on the noise in the dark region.
If there's interference-type noise just do a 2-D fft and look at the power-spectra, if that has spurious peaks (narrow at that) at high frequencies, you could use a notch-filter to reduce those components. If this is a result of a tomographic reconstruction then that seems like a very unlikely event. In the case that some noise of the original measurements (PET-detector response, variation in brightness of a x-ray detector, or something else) you'd have to do that filtering/correction before the tomographic inversion.
To simply estimate a constant background outside the bright region:
BG = mean(I(I(:)>threshold));
Where you'd have to select the threshold intensity wisely.

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