How to remove sine in FFT

Hi,

I would like to apologize for my little knowledge in FFT. However, I have several images taken with a CCD that contains a single spectral line (Gaussian) and a sinusoidal pattern. Now, I would like to remove the sinusoidal pattern via FFT which should be basically no problem. I do have exposures of just the sinusoidal patter which I use as template. I am not sure how to remove the sine in Fourier space. I just would like to summarize what I did so far:

R = reference sine S = signal (spectral line + sine)

Fs= length(R);
x = linspace(1,Fs,Fs)

% plot signals
figure();
plot(x,S); hold on
plot(x,R);
xlabel('Pixel')
ylabel('Intensity');

nfft = 1024; % Length of FFT
% Frequency vector
freq = (0:nfft/2-1)*Fs/nfft;

ff1 = fft(S,nfft);
ff2 = fft(R,nfft);

% Take the magnitude 
F1 = abs(ff1);
F2 = abs(ff2);

% plot signals
figure();
plot(freq,mF1); hold on
plot(freq,mF2);
title('Power Spectrum');
xlabel('Frequency')
ylabel('Power');

However, then all I have tried does not work properly:

% Subtract the reference from signal 
M = F1-F2; 

S_final = ifft(M);

When the signal gets back transformed it does not look like as I expected. The residual signal should be a Gaussian with some left over noise.

I would be absolutely great to help me with this issue!

Kind regards Tobias

[sixwwwwww]

Can you share some of your images for analysis?

Answer 1

[Tobias]

Hi,

here are two file of (a) sine+line (b) line. Maybe this is better than the original files.

Cheers,

Tobias