Ifft2 results do not match that of irfft2 in Pyhton

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Seyedalireza Abootorabi
编辑： Matt J 2025-2-28
Hi All,
I am using the rfft2 function in Python to get the Fourier trasnformed data and use the ifft2 function in Matlab to get back the original data.
I firstly, load the spectral data from Python
clear
clc
rfft2_real = load('rfft2_real.txt');
rfft2_imag = load('rfft2_imag.txt');
Then I construct the whole spectral domain by adding the imaginary and real terms together
% Reconstruct the complex rfft2 output
rfft2_result = rfft2_real + 1i * rfft2_imag;
since rfft2 in Python stores only the positive frequencies for one of the dimensions I had to account for the missing negative frequencies in the follwoing way:
% Compute full FFT2 result by mirroring the data
[m, n_half] = size(rfft2_result);
n = 2 * (n_half - 1); % Reconstruct full FFT size
% Reconstruct the full frequency domain
fft2_result = zeros(m, n);
fft2_result(:, 1:n_half) = rfft2_result; % Copy half-spectrum
fft2_result(:, n_half+1:n) = conj(fliplr(rfft2_result(:, 2:end-1))); % Mirror
% Compute the inverse FFT to get back the original matrix
reconstructed_x = ifft2(fft2_result)
I played with this code and it gives me the right answer for some signals but for others it does not. Anybody knows the issue?
  1 个评论
Matt J
Matt J 2025-2-28
编辑：Matt J 2025-2-28
Please provide the input data files, both the cases that give the right answer and the ones that don't.

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回答（1 个）

Matt J
Matt J 2025-2-28
编辑：Matt J 2025-2-28
I'm not a Python user, but if rfft2 only gives you positive x-frequencies, I would imagine it also only gives you positive y-frequencies as well, no? If so, why are you only mirroring across columns?

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