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copied!<p>I believe where you are stuck is that the Gaussian filter supplied by OpenCV is created in the spatial (time) domain, but you want the filter in the frequency domain. <a href="http://paulbourke.net/miscellaneous/imagefilter/" rel="noreferrer">Here</a> is a nice article on the difference between high and low-pass filtering in the frequency domain. </p> <p>Once you have a good understanding of how frequency domain filtering works, then you are ready to try to create a Gaussian Filter in the frequency domain. <a href="http://vision.yeditepe.edu.tr/EE562/files/EE469_4.pdf" rel="noreferrer">Here</a> is a good lecture on creating a few different (including Gaussian) filters in the frequency domain.</p> <p><strike>If you are still having difficulty, I will try to update my post with an example a bit later!</strike></p> <p><strong>EDIT :</strong> Here is a short example that I wrote on implementing a Gaussian high-pass filter (based on the lecture I pointed you to):</p> <pre><code>#include <opencv2/core/core.hpp> #include <opencv2/highgui/highgui.hpp> #include <iostream> using namespace cv; using namespace std; double pixelDistance(double u, double v) { return cv::sqrt(u*u + v*v); } double gaussianCoeff(double u, double v, double d0) { double d = pixelDistance(u, v); return 1.0 - cv::exp((-d*d) / (2*d0*d0)); } cv::Mat createGaussianHighPassFilter(cv::Size size, double cutoffInPixels) { Mat ghpf(size, CV_64F); cv::Point center(size.width / 2, size.height / 2); for(int u = 0; u < ghpf.rows; u++) { for(int v = 0; v < ghpf.cols; v++) { ghpf.at<double>(u, v) = gaussianCoeff(u - center.y, v - center.x, cutoffInPixels); } } return ghpf; } int main(int /*argc*/, char** /*argv*/) { Mat ghpf = createGaussianHighPassFilter(Size(128, 128), 16.0); imshow("ghpf", ghpf); waitKey(); return 0; } </code></pre> <p>This is definitely not an optimized filter generator by any means, but I tried to keep it simple and straight forward to ease understanding :) Anyway, this code displays the following filter:</p> <p><img src="https://i.stack.imgur.com/qEEmu.jpg" alt="enter image description here"></p> <p><strong>NOTE :</strong> This filter is not FFT shifted (i.e., this filter works when the DC is placed in the center instead of the upper-left corner). See the OpenCV <a href="https://code.ros.org/trac/opencv/browser/trunk/opencv/samples/cpp/dft.cpp" rel="noreferrer">dft.cpp</a> sample (lines 62 - 74 in particular) on how to perform FFT shifting in OpenCV.</p> <p>Enjoy!</p>

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