Inverse FFT in OpenCV gives different result than Matlab

Question

Using OpenCV, I want to get the same result of Matlab's ifft2 function. In Matlab I get:

A = [1 2 0; 4 5 0; 7 8 9; 10 11 12];
inverse = ifft2(A);

inverse =

   5.7500 + 0.0000i  -0.1250 + 0.3608i  -0.1250 - 0.3608i
  -1.7500 - 2.0000i  -0.3080 + 0.4665i   0.5580 + 0.0335i
  -1.2500 + 0.0000i  -0.1250 - 0.2165i  -0.1250 + 0.2165i
  -1.7500 + 2.0000i   0.5580 - 0.0335i  -0.3080 - 0.4665i

In OpenCV, when I do:

cv::Mat paddedA;
int m = cv::getOptimalDFTSize(A.rows);
int n = cv::getOptimalDFTSize(A.cols);

cv::copyMakeBorder(A, paddedA, 0, m - A.rows, 0, n - A.cols, cv::BORDER_CONSTANT, cv::Scalar::all(0));
cv::Mat planes[] = { cv::Mat_<float>(paddedA), cv::Mat::zeros(paddedA.size(), CV_32F) };
cv::Mat complexA;
cv::merge(planes, 2, complexA);

cv::Mat inverse;
cv::idft(complexA, inverse, cv::DFT_SCALE | cv::DFT_COMPLEX_OUTPUT);

This gives me:

inverse = [1, -0, 2, -0, 0, -0;
     4, -0, 5, -0, 0, -0;
     7, -0, 8, -8, 9, 0;
     10, -0, 11, -0, 12, -0]

And the type of A is CV_32F . How can I get the same result as that of Matlab?

Answer 1

You are using two different functions. FFT is optimized version of DFT. You should use step function in matlab then compare the results.