Help with 2D planer fit.

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

[Image Analyst]

What kind of filtering do you want to do?

What kind of image is this? Is it x-ray or fluorescence, or something else? I ask because if you're thinking of doing background correction, it matters what process created the image so you can know if you need to do background subtraction or background division.

[Parag]

Thank you for your reply. It's a CT image. I want to planer fit region around the disk and subtract from original image in order to get rid of noise. I don't have an idea how to fit it. I will appreciate if you provide way to do it. Thank you.

[Bjorn Gustavsson]

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.

HTH