fft

问题 Here's some code I wrote to display the magnitude spectrum of an image: orig_imdata = imread('Original_Image.png'); spec_orig = fft2(double(orig_imdata)); spec_orig2 = abs(spec_orig); spec_img = fftshift(spec_orig2); imshow(spec_img); When I comment out the use of abs and just fftshift the image, I get an image, albeit with the phase and the magnitude. If I apply the abs function right after using fftshift , I get a blank result from imshow . I need an image of the magnitude of the spectral

问题 i am trying to plot the figure of FFT magnitude of an image using the following code in the command window: a= imread('lena','png') figure,imshow(a) ffta=fft2(a) fftshift1=fftshift(ffta) magnitude=abs(fftshift1) figure,imshow(magnitude),title('magnitude') However, the figure with the title magnitude shows nothing, even though MATLAB shows that it has computed abs() on fftshift . The figure is still empty, and there is no error. Also, why do we need to compute the phase shift before magnitude?

问题 i am trying to plot the figure of FFT magnitude of an image using the following code in the command window: a= imread('lena','png') figure,imshow(a) ffta=fft2(a) fftshift1=fftshift(ffta) magnitude=abs(fftshift1) figure,imshow(magnitude),title('magnitude') However, the figure with the title magnitude shows nothing, even though MATLAB shows that it has computed abs() on fftshift . The figure is still empty, and there is no error. Also, why do we need to compute the phase shift before magnitude?

问题 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 you for any help. The code: nasa=imread('nasaNoise _1_','jpg'); N_Fourier=fft2(nasa); N_Fourier=fftshift(N_Fourier); N_Fourier=abs(N_Fourier); N_Fourier=log(N_Fourier+1); N_Fourier=mat2gray(N_Fourier); %Now doing the inverse N_inverse=ifft2(N

问题 I am trying to do a 3D FFT with the FFTW library, but I have some difficulties with the inverse transformation. At first I do the foreword transformation via: fftwf_plan_dft_3d(_dimensions[0], _dimensions[1], _dimensions[2], (fftwf_complex*)_inputBuffer, (fftwf_complex*)_outputBuffer, FFTW_FORWARD, FFTW_ESTIMATE); Although my data is real data I am using the complex to complex transformation, as want to replace it later by an opencl fft which only supports complex to complex transformations.

问题 I'm receiving PCM data trough socket connection in packets containing 320 samples. Sample rate of sound is 8000 samples per second. I am doing with it something like this: int size = 160 * 2;//160; int isinverse = 1; kiss_fft_scalar zero; memset(&zero,0,sizeof(zero)); kiss_fft_cpx fft_in[size]; kiss_fft_cpx fft_out[size]; kiss_fft_cpx fft_reconstructed[size]; kiss_fftr_cfg fft = kiss_fftr_alloc(size*2 ,0 ,0,0); kiss_fftr_cfg ifft = kiss_fftr_alloc(size*2,isinverse,0,0); for (int i = 0; i <

问题 Thanks in advance for any help on this subject. I've recently been trying to work out Parseval's theorem for discrete fourier transforms when noise is included. I based my code from this code. What I expected to see is that (as when no noise is included) the total power in the frequency domain is half that of the total power in the time-domain, as I have cut off the negative frequencies. However, as more noise is added to the time-domain signal, the total power of the fourier transform of the

问题 I have this piece of a code and I want to work independently with each of the four mic array I use (Ps3 Eye Cam). For example I want to calculate cross-correlation between the mic 1 and the mic 4 excluding 2 and 3. How can I use channels I want? import audioop import alsaaudio inp = alsaaudio.PCM(alsaaudio.PCM_CAPTURE,alsaaudio.PCM_NONBLOCK) inp.setchannels(1) inp.setrate(8000) inp.setformat(alsaaudio.PCM_FORMAT_S16_LE) inp.setperiodsize(1000) Thanks 来源： https://stackoverflow.com/questions

问题 I've a Python code which performs FFT on a wav file and plot the amplitude vs time / amplitude vs freq graphs. I want to calculate dB from these graphs (they are long arrays). I do not want to calculate exact dBA, I just want to see a linear relationship after my calculations. I've dB meter, I will compare it. Here is my code: #!/usr/bin/env python # -*- coding: utf-8 -*- from __future__ import print_function import scipy.io.wavfile as wavfile import scipy import scipy.fftpack import numpy as

问题 I've a Python code which performs FFT on a wav file and plot the amplitude vs time / amplitude vs freq graphs. I want to calculate dB from these graphs (they are long arrays). I do not want to calculate exact dBA, I just want to see a linear relationship after my calculations. I've dB meter, I will compare it. Here is my code: #!/usr/bin/env python # -*- coding: utf-8 -*- from __future__ import print_function import scipy.io.wavfile as wavfile import scipy import scipy.fftpack import numpy as