7. 对一幅灰度图像进行离散余弦变换，用图像的形式显示其变换系数。变换后去掉小于系数最大值60% 、80%、90%的系数，在进行反变换，观察变换前后图像区别。

#include <cxcore.h>
#include <cv.h>
#include <highgui.h>
void cvDcT(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;

    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(dst_arr, &d1stub, cvRect(0, 0, cx, cy));
    d2 = cvGetSubRect(dst_arr, &d2stub, cvRect(cx, 0, cx, cy));
    d3 = cvGetSubRect(dst_arr, &d3stub, cvRect(cx, cy, cx, cy));
    d4 = cvGetSubRect(dst_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);
    }
}

int main(int argc, char ** argv)
{
    const char* filename = argc >= 2 ? argv[1] : "2.bmp";
    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("6013202130.bmp", CV_LOAD_IMAGE_GRAYSCALE);
    if (!im)
        return -1;
    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);
    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);
    }
    cvDFT(dft_A, dft_A, CV_DXT_FORWARD, complexInput->height);
    cvNamedWindow("原图6013202130", 0);
    cvNamedWindow("变换后", 0);
    cvShowImage("原图6013202130", im);
    cvSplit(dft_A, image_Re, image_Im, 0, 0);
    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);
    cvAddS(image_Re, cvScalarAll(1.0), image_Re, NULL);
    cvLog(image_Re, image_Re);
    cvDcT(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("变换后", image_Re);
    cvWaitKey(-1);
    return 0;
}