opencv/samples/octave/dft.m

#! /usr/bin/env octave
cv;
highgui;

## Rearrange the quadrants of Fourier image so that the origin is at
## the image center
## src & dst arrays of equal size & type
function cvShiftDFT(src_arr, dst_arr )

  size = cvGetSize(src_arr);
  dst_size = cvGetSize(dst_arr);

  if(dst_size.width != size.width || \
     dst_size.height != size.height)
    cvError( CV_StsUnmatchedSizes, "cvShiftDFT", \
	    "Source and Destination arrays must have equal sizes", \
	    __FILE__, __LINE__ );    
  endif

  if(swig_this(src_arr) == swig_this(dst_arr))
    tmp = cvCreateMat(size.height/2, size.width/2, cvGetElemType(src_arr));
  endif
  
  cx = size.width/2;
  cy = size.height/2; # image center

  q1 = cvGetSubRect( src_arr, cvRect(0,0,cx, cy) );
  q2 = cvGetSubRect( src_arr, cvRect(cx,0,cx,cy) );
  q3 = cvGetSubRect( src_arr, cvRect(cx,cy,cx,cy) );
  q4 = cvGetSubRect( src_arr, cvRect(0,cy,cx,cy) );
  d1 = cvGetSubRect( src_arr, cvRect(0,0,cx,cy) );
  d2 = cvGetSubRect( src_arr, cvRect(cx,0,cx,cy) );
  d3 = cvGetSubRect( src_arr, cvRect(cx,cy,cx,cy) );
  d4 = cvGetSubRect( src_arr, cvRect(0,cy,cx,cy) );

  if(swig_this(src_arr) != swig_this(dst_arr))
    if( !CV_ARE_TYPES_EQ( q1, d1 ))
      cvError( CV_StsUnmatchedFormats, \
	      "cvShiftDFT", "Source and Destination arrays must have the same format", \
	      __FILE__, __LINE__ );    
    endif
    
    cvCopy(q3, d1);
    cvCopy(q4, d2);
    cvCopy(q1, d3);
    cvCopy(q2, d4);
    
  else
    cvCopy(q3, tmp);
    cvCopy(q1, q3);
    cvCopy(tmp, q1);
    cvCopy(q4, tmp);
    cvCopy(q2, q4);
    cvCopy(tmp, q2);
  endif
endfunction


im = cvLoadImage( argv(){1}, CV_LOAD_IMAGE_GRAYSCALE);

realInput = cvCreateImage( cvGetSize(im), IPL_DEPTH_64F, 1);
imaginaryInput = cvCreateImage( cvGetSize(im), IPL_DEPTH_64F, 1);
complexInput = cvCreateImage( cvGetSize(im), IPL_DEPTH_64F, 2);

cvScale(im, realInput, 1.0, 0.0);
cvZero(imaginaryInput);
cvMerge(realInput, imaginaryInput, [], [], complexInput);

dft_M = cvGetOptimalDFTSize( im.height - 1 );
dft_N = cvGetOptimalDFTSize( im.width - 1 );

dft_A = cvCreateMat( dft_M, dft_N, CV_64FC2 );
image_Re = cvCreateImage( cvSize(dft_N, dft_M), IPL_DEPTH_64F, 1);
image_Im = cvCreateImage( cvSize(dft_N, dft_M), IPL_DEPTH_64F, 1);

## copy A to dft_A and pad dft_A with zeros
tmp = cvGetSubRect( dft_A, cvRect(0,0, im.width, im.height));
cvCopy( complexInput, tmp, [] );
if(dft_A.width > im.width)
  tmp = cvGetSubRect( dft_A, cvRect(im.width,0, dft_N - im.width, im.height));
  cvZero( tmp );
endif

## no need to pad bottom part of dft_A with zeros because of
## use nonzero_rows parameter in cvDFT() call below

cvDFT( dft_A, dft_A, CV_DXT_FORWARD, complexInput.height );

cvNamedWindow("win", 0);
cvNamedWindow("magnitude", 0);
cvShowImage("win", im);

## Split Fourier in real and imaginary parts
cvSplit( dft_A, image_Re, image_Im, [], [] );

## Compute the magnitude of the spectrum Mag = sqrt(Re^2 + Im^2)
cvPow( image_Re, image_Re, 2.0);
cvPow( image_Im, image_Im, 2.0);
cvAdd( image_Re, image_Im, image_Re, []);
cvPow( image_Re, image_Re, 0.5 );

## Compute log(1 + Mag)
cvAddS( image_Re, cvScalarAll(1.0), image_Re, [] ); # 1 + Mag
cvLog( image_Re, image_Re ); # log(1 + Mag)


## Rearrange the quadrants of Fourier image so that the origin is at
## the image center
cvShiftDFT( image_Re, image_Re );

[min, max] = cvMinMaxLoc(image_Re);
cvScale(image_Re, image_Re, 1.0/(max-min), 1.0*(-min)/(max-min));
cvShowImage("magnitude", image_Re);

cvWaitKey(-1);