离散傅立叶变换(DFT)

void cvShiftDFT(CvArr * src_arr, CvArr * dst_arr )
{
CvMat * tmp;
CvMat q1stub, q2stub;
CvMat q3stub, q4stub;
CvMat d1stub, d2stub;
CvMat d3stub, d4stub;
CvMat * q1, * q2, * q3, * q4;
CvMat * d1, * d2, * d3, * d4;

CvSize size = cvGetSize(src_arr);
CvSize dst_size = cvGetSize(dst_arr);
int cx, cy;

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__ );
}

if(src_arr==dst_arr){
tmp = cvCreateMat(size.height/2, size.width/2, cvGetElemType(src_arr));
}

cx = size.width/2;
cy = size.height/2; // image center

q1 = cvGetSubRect( src_arr, &q1stub, cvRect(0,0,cx, cy) );
q2 = cvGetSubRect( src_arr, &q2stub, cvRect(cx,0,cx,cy) );
q3 = cvGetSubRect( src_arr, &q3stub, cvRect(cx,cy,cx,cy) );
q4 = cvGetSubRect( src_arr, &q4stub, cvRect(0,cy,cx,cy) );
d1 = cvGetSubRect( src_arr, &d1stub, cvRect(0,0,cx,cy) );
d2 = cvGetSubRect( src_arr, &d2stub, cvRect(cx,0,cx,cy) );
d3 = cvGetSubRect( src_arr, &d3stub, cvRect(cx,cy,cx,cy) );
d4 = cvGetSubRect( src_arr, &d4stub, cvRect(0,cy,cx,cy) );

if(src_arr!=dst_arr){
if( !CV_ARE_TYPES_EQ( q1, d1 )){
cvError( CV_StsUnmatchedFormats, "cvShiftDFT", "Source and Destination arrays must have the same format", __FILE__, __LINE__ );
}
cvCopy(q3, d1, 0);
cvCopy(q4, d2, 0);
cvCopy(q1, d3, 0);
cvCopy(q2, d4, 0);
}
else{
cvCopy(q3, tmp, 0);
cvCopy(q1, q3, 0);
cvCopy(tmp, q1, 0);
cvCopy(q4, tmp, 0);
cvCopy(q2, q4, 0);
cvCopy(tmp, q2, 0);
}
}

void change()
{
IplImage * im;

IplImage * realInput;
IplImage * imaginaryInput;
IplImage * complexInput;
int dft_M, dft_N;
CvMat* dft_A, tmp;
IplImage * image_Re;
IplImage * image_Im;
double m, M;

im = cvLoadImage("first2.bmp", CV_LOAD_IMAGE_GRAYSCALE );
if( !im )
return;

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, NULL, NULL, 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
cvGetSubRect( dft_A, &tmp, cvRect(0,0, im->width, im->height));
cvCopy( complexInput, &tmp, NULL );
if( dft_A->cols > im->width )
{
cvGetSubRect( dft_A, &tmp, cvRect(im->width,0, dft_A->cols - im->width, im->height));
cvZero( &tmp );
}

// 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, 0, 0 );

// 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, NULL);
cvPow( image_Re, image_Re, 0.5 );

// Compute log(1 + Mag)
cvAddS( image_Re, cvScalarAll(1.0), image_Re, NULL ); // 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 );

cvMinMaxLoc(image_Re, &m, &M, NULL, NULL, NULL);
cvScale(image_Re, image_Re, 1.0/(M-m), 1.0*(-m)/(M-m));
cvShowImage("magnitude", image_Re);

cvWaitKey(-1);
}