opencv 实现傅里叶变换,必须承认工程师、码农还真的不是一回事,做个笔记保存下吧先,傅里叶还真的看不明白!!!
代码:
int main()
{
//C:/Users/liyihang/Desktop/sc/out.png
Mat I = imread("C:/Users/liyihang/Desktop/sc/out.png", IMREAD_GRAYSCALE); //读入图像灰度图
//判断图像是否加载成功
if (I.empty())
{
cout << "图像加载失败!" << endl;
return -1;
}
else
cout << "图像加载成功!" << endl << endl;
Mat padded; //以0填充输入图像矩阵
int m = getOptimalDFTSize(I.rows);
int n = getOptimalDFTSize(I.cols);
//填充输入图像I,输入矩阵为padded,上方和左方不做填充处理
copyMakeBorder(I, padded, 0, m - I.rows, 0, n - I.cols, BORDER_CONSTANT, Scalar::all(0));
Mat planes[] = { Mat_<float>(padded), Mat::zeros(padded.size(),CV_32F) };
Mat complexI;
merge(planes, 2, complexI); //将planes融合合并成一个多通道数组complexI
dft(complexI, complexI); //进行傅里叶变换
//计算幅值,转换到对数尺度(logarithmic scale)
//=> log(1 + sqrt(Re(DFT(I))^2 + Im(DFT(I))^2))
split(complexI, planes); //planes[0] = Re(DFT(I),planes[1] = Im(DFT(I))
//即planes[0]为实部,planes[1]为虚部
magnitude(planes[0], planes[1], planes[0]); //planes[0] = magnitude
Mat magI = planes[0];
magI += Scalar::all(1);
log(magI, magI); //转换到对数尺度(logarithmic scale)
//如果有奇数行或列,则对频谱进行裁剪
magI = magI(Rect(0, 0, magI.cols & -2, magI.rows & -2));
//重新排列傅里叶图像中的象限,使得原点位于图像中心
int cx = magI.cols / 2;
int cy = magI.rows / 2;
Mat q0(magI, Rect(0, 0, cx, cy)); //左上角图像划定ROI区域
Mat q1(magI, Rect(cx, 0, cx, cy)); //右上角图像
Mat q2(magI, Rect(0, cy, cx, cy)); //左下角图像
Mat q3(magI, Rect(cx, cy, cx, cy)); //右下角图像
//变换左上角和右下角象限
Mat tmp;
q0.copyTo(tmp);
q3.copyTo(q0);
tmp.copyTo(q3);
//变换右上角和左下角象限
q1.copyTo(tmp);
q2.copyTo(q1);
tmp.copyTo(q2);
//归一化处理,用0-1之间的浮点数将矩阵变换为可视的图像格式
normalize(magI, magI, 0, 1, NORM_MINMAX);
imshow("输入图像", I);
imshow("频谱图", magI);
waitKey(0);
return 0;
}