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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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Finding the Inverse Fourier Transform from Phase Information Only

I am new to image processing. I have made a program on Discrete Fourier Transform. I am able to get an inverse image from (magnitude + phase) information. Also I am able to get inverse image from only magnitude part but I am not able to get the…
sony
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Speed up IFFT calculation in Python

I am working on a Python program (in Enthought Canopy) that will calculate the two point autocorrelation function for 2 and 3 dimensional images. The core of the calculation is the following code: fftx = fftn(newimpad) del newimpad ret_int = (fftx…
LM Anovitz
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FFTW - computing the IFFT without first computing an FFT

This may seem like a simple question but I've been trying to find the answer on the FFTW page and I am unable to. I created the FFTW plans for forward and backward transforms and I fed some data into the fftw_complex *fft structure directly (instead…
user3936766
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Converting fft to ifft in C#

I have a working FFT, but my question is how do I convert it into an IFFT? I was told that an IFFT should be just like the FFT that you are using. so how do I make an ifft from a fft i c#? I was told there should only be a few changes made to get…
Brandon Boone
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Phase vocoder - synthesis window needed?

I've been struggling for a few weeks on a phase vocoder. The ultimate goal is achieving time stretching of a signal. I've been making a lot of progress, but I still have two issues to solve. Issue1: Do I need a synthesis window?. I take overlapping…
Merlevede
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Overlap add for signal synthesis

I apologize if this question is very basic. I'm transforming an audio signal (currently a plain sine wave) from the time-domain to the frequency-domain using FFT, and then back to the time-domain to compare the difference to the original…
Merlevede
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Creating real signals out of a frequency response and associated phase response

I'm trying to create real signals like a sine wave or a sine sweep in MATLAB. Since I want to go deep into the theory of the discrete Fourier transform, I'm trying to create those signals through defining a vector for my frequency response and the…
user967493
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ifft of a gaussian function in matlab

I have analytically calculated the FFT of a Gaussian function (with zero mean). Now I want to take numerical IFFT of that using MATLAB codes. Since I am new in MATLAB, I need help in doing this. Thank you in advance.
user3221839
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How to determine frequency in time dimension using FFT and IFFT on 3D Matrix

Currently, I working on a assignment to obtain few frames from a movie file played in Matlab. A 3D Matrix was created in parameter X,Y and time. But I been asked to determine the frequency in time by using FFT and IFFT. My problem is how to plot the…
E.Lee
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Single Precision math slower than Double Precision in FFTW?

I am looking at the benchmarks of FFT library and wondering why double precision math would be faster than that of the single precision (even on a 32-bit hardware).
VJ Vélan Solutions
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inverse fourier transform manual merge of real and imaginary

I'm making a couple of wrapper methods for fourier transform of image and have encountered a problem. Whenever I use the standard methods: void fft::dfft(Mat* img,Mat* result){ Mat image; img->convertTo(image, CV_32F); cv::dft(image,…
user3002166
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symmetric FFT in matlab

I'm going to implement OFDM system in matlab. I need to take IFFT symmetric from data and then again FFT from results. the IFFT goes right, but the FFT doesn't, fisrt half of result numbers are like data bef0r IFFT, but second half is wrong. I just…
Beh
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Fourier Transform: getting mag + phase then using those to plot original signal

Hi guy's I'm working on simple signals and I want to calculate the Fourier transform of a signal, get the magnitude and phases, then reconstruct the original signal from that. I'm basing my code on this thread. Code: >> n=0:99; >> N=length(n); >> x…
kir
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Why isn't the inverse Fourier transform giving the correct results?

I took the Fourier transform of an image in Matlab and now I want to take the inverse fourier but the result is a completely black picture instead of the original image. I think there is some step that I need to do before taking the inverse. Thank…
user2948218
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How SOA based Signal Processing?

I am working on a problem regarding noise removal from recorded signals using some Adaptive Filtering ( e.g Wiener Filter ). It's a typical DSP problem in a following way. Recording Time Signals Windowing into Blocks FFT Performing Noise…
Usman
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