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Questions tagged [ifft]

NOTE: please use the FFT tag instead. The FFT is a type of algorithm for quickly computing the Inverse Discrete Fourier Transform.

The IFFT is an FFT algorithm with some different initial permutation of data samples, and often an additional normalization, such that the algorithm computes the IDFT rather than the DFT. The FFT and IFFT are always implemented by the same code.

Related topics include , , , .

More information on the IFFT can be found in the Wikipedia article on the FFT

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OpenCV IDFT has strange noise and high pass filter result seem wrong

Platform: opencv 2.4.9 on win7 with VC2015 Issue: Input image DFT magnitude image strange noise: I use dft transfer image into frequency domain and transfer back by idft. I use 2 ways to get the result. convertTo() and normalize(). the result by…
Chi-Fang Hsieh
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In python, If I perform an fft on complex data, then irfft only the positive frequencies, how does that affect the data?

So I am trying to perform a frequency shift on a set of real valued points. In order to achieve a frequency shift, one has to multiply the data by a complex exponential, making the resulting data complex. If I multiply by just a cosine I get…
jmurray1241
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IFFT and frequency information

Suppose there is a real signal Amp_time (Amplitude as a function of time) at Sample Rate SampRate. I can transform it into frequency domain with fftLength = length(Amp_time); FT_freq = fft(Amp_time,fftLength); % signal as a function of…
Lukas
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fftshift / ifftshift in terms of circshift

and am trying to relate fftshift/ifftshift to circular shift. N = 5 Y = 0:N-1 X = [0 1 2 3 4] When I fftshift(X), I get [3 4 0 1 2] When I ifftshift(X), I get [2 3 4 0 1] How do I relate fftshift/ifftshift to circular shift? Is it simply…
lppier
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arduino fft and matlab ifft

We currently work with Arduino. I am using the fft library of "open music labs FFT library" My question is two things. Arduino code issues Inverse fft in Matlab (With the FFT results from Arduino) the following code using Arduino FFT library for…
skzlzl
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Inverse Fourier transform involving 3 wavenumbers (3D) in Matlab

I was solving PDE (Stokes equation to be specific) in Fourier space. The PDE was in 3 dimension and I had three wavenumbers namely, (k1,k2 and k3) for three directions. I am confused with using ifft of Matlab to get the solution in real space. I am…
Brato
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Approximate a signal using average value and dominant frequency

I have a signal x[n], transformed it using fft and extracted the dominant frequency by sorting the amplitude response. Calculated average as avg = mean(xn) , where xn is a 1x3142 matrix containing the signal data. How do I use this information to…
Lightvvind
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Numpy ifft error

I'm having a really frustrating problem using numpy's inverse fast fourier transform function. I know the fft function works well based on my other results. Error seems to be introduced after calling ifft. The following should be printing zeros…
Jacob Edison
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How to create the complex representation from magnitude and phase information to perform an inverse fast fourier transform(IFFT)?

I have a problem with converting amplitude and phase data into the complex form, which is required to perform an IFFT. (inverse fast fourier transform). This is the only data I have. My frequency range goes from 0.1 to 2.6 and, with 200 samples. I…
Moon
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Matlab's ifft2 function in OpenCV

I've already searched a lot on the internet but still haven't come across with a solution. What I want is to convert the Matlab's ifft2 function into OpenCV to obtain the same result. For instance, if I have a 10x10 matrix A as: A = 11 22 …
E_learner
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FFT - Filtering - Inverse FFT - Offset remaining

I'm doing the following: Perform a FFT / Cut every frequency above 100Hz in the FFT results / Perform an Inverse-FFT It works well... if the original dataset doesn't have an offset ! If it has an offset, the output result magnitude is…
Lmecano
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Using a periodic wave as an inverse transform block

I have a question regarding the PeriodicWave in Web Audio API. Take a look at the following code: https://slack-files.com/T04PVA27V-F051SS7LD-a71e14c8a2 For every iteration of the script processor, I get different values for the channel data 0.…
echo66
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Inverse fast fourier transform: different phases

RosettaCode gives a simple implementation of the Cooley–Tukey FFT algorithm here. The question is the following and is from a mathematical and programming point of view. Suppose that an input of a program is the spectrum of a signal, and we want to…
Vincent
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FFT Multiplication Python 3.4.3

I have an FFT and IFFT functions. And i know that A*B = IFFT(FFT(A)*FFT(B)) Where FFT(A)FFT(B)=[qw for q,w in zip(A,B)] But when i input: 10 10 => output: [(0.5+0j), (0.5+0j)] What i`m doing wrong? Here is my code: from cmath import…
Reodont
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Generating movement based on time t for real time ocean waves from an initial spectrum

I've spent the last week or so rendering a simple ocean using gerstner waves but having issues with tiling, so I decided to start rendering them "properly" and dip my toes into the murky waters of rendering a heightfield using an iFFT. There are…
Lloyd Crawley
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