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Questions tagged [dft]

Discrete Fourier transform (DFT) is a specific kind of discrete transform, used in Fourier analysis.

Given a sequence of N samples f(n), indexed by n = 0..N-1, the discrete Fourier transform (DFT) is defined as F(k), where k=0..N-1:

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Source: engineeringproductivitytools

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OpenCV find image frequencies

I am trying to find the dominant frequencies in an image using OpenCV. I saw the dft example in the OpenCV tutorial but how can I find the dominant frequencies of an image with periodic structures? I want to extract the spectral informations of the…
marc
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Comparative analysis of Fast Fourier Transform (FFT) algorithms on Android?

Has anyone done a comparative analysis of Fast Fourier Transform (FFT) algorithms on Android platform? Which implementation is the fastest so far?
Danijel
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How to apply Gaussian filter to DFT output in OpenCV

I want to create a Gaussian high-pass filter after determining the correct padding size (e.g., if image width and height is 10X10, then should be 20X20). I have Matlab code that I am trying to port in OpenCV, but I am having difficulty properly…
wolvorinePk
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Unexpected result from discrete fourier spectrum analysis of sine-sample

http://jvalentino2.tripod.com/dft/index.html My code is really just a copy of the above: package it.vigtig.realtime.fourier; import java.io.File; import java.io.IOException; import javax.sound.sampled.AudioFormat; import…
Felix
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How can I transfer a discrete signal from the time domain into the frequency domain and back without losing data?

For a few weeks now, I have been trying to implement a DFT that takes an arbitrary set of bytes and treats them as a signal. It then transforms them to the frequency domain. Following that it transforms them back. It originally only attempted to use…
Matt
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Extracting the outline of an image as a continuous path using opencv

Background So I am currently working on a project that is an extension of the coding train's Fourier transform series. Huge shoutout to him for inspiring this project! After watching his video on the Fourier transform of the coding train logo, I…
Krishna
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Fast Fourier Transform Optimization - How To Pre Calculate Exponential?

Actually, I think that I get the discrete Fourier transform some basics. And now I have some problems with the fast Fourier transform algorithm. I don't want to share all the functions so as not to complicate the problem. But if you don't understand…
badcode
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How to understand the result of Discrete Fourier Transform under period finding?

I am learning how to use Discrete Fourier Transform(DFT) to find the period about a^x mod(N), in which x is a positive integer, a is any prime number, and N is the product of two prime factors p and q. For example, the period of 2^x mod(15) is…
da_miao_zi
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FFT calculation in Javascript of vibration data

Question:- I have to calculate the FFT of time series data. Time series data of what ? I have a Vibration sensor that is giving me the data of displacement in x and y coordinate. What are the Problems? I can't find a proper library to work although…
WOLFIE
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DFT(discrete fourier transform) using matlab

I have some problems with transforming my data to the f-k domain. I could see many examples on this site about DFT using Matlab. But each of them has little difference. Their process is almost the same, but there is a difference in the DFT…
Hak-Min Lee
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There are different results when I take FFT sinc(t)

The first situation: %% Analytical calculation syms t f h = @(f) int(sinc(t)*exp(-1i*2*pi*f*t),t,-10,10); subplot(2,1,1); fplot(real(h(f)),[-3 3]); grid; ylim([-3 3]); subplot(2,1,2); fplot(imag(h(f)),[-3 3]); grid; ylim([-3 3]); The second…
Григорий Гуляев
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How to properly set LDOS source function in MEEP?

So I'm pretty new to FDTD modelling, and I'm having trouble interpreting the LDOS output that I am recieving from MEEP. To simplify the problem I started with a simple silver grating in a Bloch wave surface plasmon polariton (BW-SPP)…
I8Shakespeare
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Spectrogram generation in java using FFT on a .wav file not producing expected output

So I am making an AI project that classifies speech into either "up", "down", "left", right or background noise, and from this, a character in a videogame is moved. I have made an FFT algorithm deriving it from the mathematical explanation, which I…
Nathan Evans
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How to sample .svg file in javaScript?

recently i have been learning the Fourier transform and Fourier series. I was inspired by 3Blue1Brown's video and i started working on my own program of the circles drawing machine which he has represented in his video. Sadly python's graphic…
Itay2924
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CUDA convolutionFFT2D example - I can't understand it

I studied the Cooley Tukey algorithm and I understood it. I got everything in the CUDA convolutionFFT2D example till these kernels: spProcess2D calls -> spProcess2D_kernel which calls a lot of -> spPostprocessC2C, mulAndScale and…
Marco A.
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