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POHow to do inverse DFT in OpenCV
 

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  1. POHow to do inverse DFT in OpenCV
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    <p>I'm trying to implement inverse DFT using OpenCV in C++ I downloaded complete dft example in docs.opencv.org and just adjust couple of lines to inverse.</p> <p>my DFT code is like this</p> <pre><code>Mat DFT(const char* filename) { Mat I = imread(filename, CV_LOAD_IMAGE_GRAYSCALE); if (I.empty()) { Mat emty(7, 7, CV_32FC2, Scalar(1, 3)); return emty; } Mat padded; //expand input image to optimal size int m = getOptimalDFTSize(I.rows); int n = getOptimalDFTSize(I.cols); // on the border add zero values copyMakeBorder(I, padded, 0, m - I.rows, 0, n - I.cols, BORDER_CONSTANT, Scalar::all(0)); Mat planes[] = { Mat_&lt;float&gt;(padded), Mat::zeros(padded.size(), CV_32F) }; Mat complexI; merge(planes, 2, complexI); // Add to the expanded another plane with zeros dft(complexI, complexI); // this way the result may fit in the source matrix // compute the magnitude and switch to logarithmic scale // =&gt; log(1 + sqrt(Re(DFT(I))^2 + Im(DFT(I))^2)) split(complexI, planes); // planes[0] = Re(DFT(I), planes[1] = Im(DFT(I)) magnitude(planes[0], planes[1], planes[0]);// planes[0] = magnitude Mat magI = planes[0]; magI += Scalar::all(1); // switch to logarithmic scale log(magI, magI); normalize(magI, magI, 0, 1, CV_MINMAX); // Transform the matrix with float values into a // viewable image form (float between values 0 and 1). imshow("Input Image", I); // Show the result imshow(filename, magI); // waitKey(); return magI; } </code></pre> <p>and did IDFT. By just fix dft to idft. But the output was just look like noise. What did I do wrong? I thought the dft and idft is just same....</p> <pre><code>Mat IDFT(Mat src) { Mat I = src; Mat padded; //expand input image to optimal size int m = getOptimalDFTSize(I.rows); int n = getOptimalDFTSize(I.cols); // on the border add zero values copyMakeBorder(I, padded, 0, m - I.rows, 0, n - I.cols, BORDER_CONSTANT, Scalar::all(0)); Mat planes[] = { Mat_&lt;float&gt;(padded), Mat::zeros(padded.size(), CV_32F) }; Mat complexI; merge(planes, 2, complexI); // Add to the expanded another plane with zeros dft(complexI, complexI, DFT_INVERSE); // this way the result may fit in the source matrix // compute the magnitude and switch to logarithmic scale // =&gt; log(1 + sqrt(Re(IDFT(I))^2 + Im(IDFT(I))^2)) split(complexI, planes); // planes[0] = Re(IDFT(I), planes[1] = Im(IDFT(I)) magnitude(planes[0], planes[1], planes[0]);// planes[0] = magnitude Mat magI = planes[0]; magI += Scalar::all(1); // switch to logarithmic scale log(magI, magI); normalize(magI, magI, 0, 1, CV_MINMAX); imshow("forged map", magI); return magI; } </code></pre>
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