FFT with FFTW Example

Nov 4, 2008 | Tags: OpenCV | del.icio.us del.icio.us | digg Digg

FFTW is a collection of C routines for computing DFTs. It's very fast and freely available at http://www.fftw.org. Here's an example on how to compute the DFT of an array with FFTW and inverse the result back.

Listing 1: fft.c

  1. /*
  2.  * fft.c: compute FFT and IFFT from an array
  3.  */
  4. #include <stdio.h>
  5. #include <fftw3.h>
  6.  
  7. #define SIZE 4
  8.  
  9. int main( int argc, char** argv )
  10. {
  11.     double          input[SIZE] = { 1.0, 1.0, 1.0, 1.0 };
  12.     fftw_complex    *data, *fft_result, *ifft_result;
  13.     fftw_plan       plan_forward, plan_backward;
  14.     int             i;
  15.    
  16.     data        = ( fftw_complex* ) fftw_malloc( sizeof( fftw_complex ) * SIZE );
  17.     fft_result  = ( fftw_complex* ) fftw_malloc( sizeof( fftw_complex ) * SIZE );
  18.     ifft_result = ( fftw_complex* ) fftw_malloc( sizeof( fftw_complex ) * SIZE );
  19.    
  20.     plan_forward  = fftw_plan_dft_1d( SIZE, data, fft_result, FFTW_FORWARD, FFTW_ESTIMATE );
  21.     plan_backward = fftw_plan_dft_1d( SIZE, fft_result, ifft_result, FFTW_BACKWARD, FFTW_ESTIMATE );
  22.    
  23.     /* populate input data */
  24.     for( i = 0 ; i < SIZE ; i++ ) {
  25.         data[i][0] = input[i];
  26.         data[i][1] = 0.0;
  27.     }
  28.  
  29.     /* print initial data */
  30.     for( i = 0 ; i < SIZE ; i++ ) {
  31.         fprintf( stdout, "data[%d] = { %2.2f, %2.2f }\n",
  32.                     i, data[i][0], data[i][1] );
  33.     }
  34.    
  35.     fftw_execute( plan_forward );
  36.    
  37.     /* print fft result */
  38.     for( i = 0 ; i < SIZE ; i++ ) {
  39.         fprintf( stdout, "fft_result[%d] = { %2.2f, %2.2f }\n",
  40.                     i, fft_result[i][0], fft_result[i][1] );
  41.     }
  42.  
  43.     fftw_execute( plan_backward );
  44.  
  45.     /* print ifft result */
  46.     for( i = 0 ; i < SIZE ; i++ ) {
  47.         fprintf( stdout, "ifft_result[%d] = { %2.2f, %2.2f }\n",
  48.                     i, ifft_result[i][0] / SIZE, ifft_result[i][1] / SIZE );
  49.     }
  50.  
  51.     /* free memory */
  52.     fftw_destroy_plan( plan_forward );
  53.     fftw_destroy_plan( plan_backward );
  54.  
  55.     fftw_free( data );
  56.     fftw_free( fft_result );
  57.     fftw_free( ifft_result );
  58.    
  59.     return 0;
  60. }

Related Articles

10 Comments

Pavanakumar on Oct 6, 2008:

Thanks Nash, your FFTW code was very useful to me.

Swati Sharma on Dec 14, 2008:

Hi Nash, Good work on FFTW. Need help,Can you please help me with .lib files for FFTW in windows. I am getting linker error and i dont have any .lib file. Thanks Swati

Nash on Dec 14, 2008:

I've send you email. please check your inbox

Dasu on Jan 25, 2009:

Hello Nash, it is very useful source code. Can you please send me FFTW source code for computing large scale invariant and rotation.

Deena on Apr 15, 2009:

Hi Nash,
Can you send me FFTW3.h to me too. Thanks ~Deena.

Nash on Apr 15, 2009:

You can download it from fftw site.

Deena on Apr 16, 2009:

Hi again,
how come there are a few error regarding to unresolved symbol for the following:

fftw_destroy_plan(plan_f);
fftw_destroy_plan(plan_b);
fftw_free(data_in);
fftw_free(fft);
fftw_free(ifft);

thanks.

Nash on Apr 16, 2009:

Get gcc and compile with:

gcc fft.c -o fft -I"C:\fftw" -L"C:\fftw" -lfftw3-3

Replace C:\fftw with the directory where you installed fftw.

alejachipia on Jul 19, 2009:

hey thanks for publish this code, it was very helpful

Gearoid Murphy on Aug 23, 2009:

Thanks for the code, examples like this always lessen the pain of grappling with complex relatively undocumented libraries

Leave a comment

Name (required)
Email (will not be published) (required)
Website

Characters left = 1000

Tags

Correlation  HTTP  Image  Networking  OpenCV  PHP  Projects  Regex  SEO  Security  WebService 

Recent Posts

  1. OpenCV Utility: Reading Image Pixels Value
  2. OpenCV Circular ROI
  3. OpenCV 2.0 Installation on Windows XP and Visual Studio 2008
  4. Runtime ROI Selection using Mouse
  5. Real Time Eye Tracking and Blink Detection
View Archives

About the Author

avatar Cool PHP programmer writing cool PHP scripts. Feel free to contact
Tel. +62 31 8662872
+62 856 338 6017
ICQ 489571630
Skype dede_bl4ckheart
Yahoo dede_bl4ckheart
Google nashruddin.amin

Recommended Sites:

Hacker's HTTP Client
HTML and CSS Tutorials
Stop Dreaming Start Action
Online Quran and Translation