# fft2 of interferometric image - how to interpret the result in term of dominant frequency

I have an interferometric image which shows fringes at a certain frequency, basically a dominantly periodic signal overlaying the information that I want to extracthere are the fringes that I want to remove. The size of the image is 1024x4067 pixels. So using matlab I performed fft2(im,n) with n = size of image, giving me this fft-image, with maximum values given at (9,24) and it's symetric (1017,4045). I am totally confused now as of how to interprete this result. Does that mean I have a frequency of 9 in y and 24 in x direction making it some sort of Acos(2pi/9y+2pi/24x)+Bisin(2pi/9y+2pi/24x) wave!? I'm guessing this it totally wrong and stupid, but I'm really confused.. :-/ thanks for your help!

here is the shifted FFT image!

• It doesn't look like you have used 'fftshift' on this spectrum (please see: uk.mathworks.com/help/matlab/ref/fftshift.html ). Can you please obtain the 2D FFT of a number of your fringe patterns (2-3) and post it along? From the attached image, it doesn't look like your fringe pattern is periodic but maybe you can still filter its effect. – A_A Apr 8 '15 at 7:42
• I added the shiftet image to the original question. I dont understand what you mean with "Can you please obtain the 2D FFT of a number of your fringe patterns (2-3)"... – uetli Apr 8 '15 at 8:33
• Thank you. What I am trying to say is, is the fringe pattern consistent across different acquisitions? If not, can you obtain 2-3 different fringe patterns and their spectra? – A_A Apr 8 '15 at 13:38
• I just have this one acquisition unfortuntely... :-( – uetli Apr 9 '15 at 6:33