How to show noise spectrum from a grayimage

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Hello, please help me solve this problem. I have a grayimage with lots of noise (don't know the type of noise). I want to draw noise spectrum. So how can i do?

Accepted Answer

Image Analyst
Image Analyst on 1 Dec 2015
First get the noise image alone. To get this you'll have to know/have the noise-free image. Then call fft2(). If you don't have a noise-free image, then the best you can do is to get the spectrum of the noise+(true image) together, rather than the noise alone.
  3 Comments
Image Analyst
Image Analyst on 1 Dec 2015
How do you know that's not true signal? Of course we know that all images have noise. If you want, you can synthesize an image where you have uniform gray levels in the regions, then subtract that "perfect" image from your actual image. Then call fft2()
noiseImage = double(actualImage) - double(perfectImage);
fftImage = fft2(noiseImage);
magSpectrum = log(abs(fftImage));
imshow(magSpectrum, []);
Helen Sky
Helen Sky on 4 Dec 2015
Thank you very much. Now i understand what to do.

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