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POMasking frequencies in a Fourier Transform
 

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    <p>I'm messing around with OpenCV, and am trying to do some of the same stuff signal processing stuff I've done in MatLab. I'm looking to mask out some frequencies, so I have constructed a matrix which will do this. The problem is that there seem to be a few more steps in OpenCV than in Matlab to accomplish this.<br> In Matlab, it's simple enough:</p> <pre><code>F = fft2(image); smoothF = F .* mask; // multiply FT by mask smooth = ifft2(smoothF); // do inverse FT </code></pre> <p>But I'm having trouble doing the same in OpenCV. The DFT leaves me with a 2 channel image, so I've split the image, multiplied by the mask, merged it back, and then perform the inverse DFT. However, I got a weird result in my final image. I'm pretty sure I'm missing something...</p> <pre><code>CvMat* maskImage(CvMat* im, int maskWidth, int maskHeight) { CvMat* mask = cvCreateMat(im-&gt;rows, im-&gt;cols, CV_64FC1); cvZero(mask); int cx, cy; cx = mask-&gt;cols/2; cy = mask-&gt;rows/2; int left_x = cx - maskWidth; int right_x = cx + maskWidth; int top_y = cy + maskHeight; int bottom_y = cy - maskHeight; //create mask for(int i = bottom_y; i &lt; top_y; i++) { for(int j = left_x; j &lt; right_x; j++) { cvmSet(mask,i,j,1.0f); // Set M(i,j) } } cvShiftDFT(mask, mask); IplImage* maskImage, stub; maskImage = cvGetImage(mask, &amp;stub); cvNamedWindow("mask", 0); cvShowImage("mask", maskImage); CvMat* real = cvCreateMat(im-&gt;rows, im-&gt;cols, CV_64FC1); CvMat* imag = cvCreateMat(im-&gt;rows, im-&gt;cols, CV_64FC1); cvSplit(im, imag, real, NULL, NULL); cvMul(real, mask, real); cvMul(imag, mask, imag); cvMerge(real, imag, NULL, NULL, im); IplImage* maskedImage; maskedImage = cvGetImage(imag, &amp;stub); cvNamedWindow("masked", 0); cvShowImage("masked", maskedImage); return im; } </code></pre>
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    1. COcould you also post the lines where you call this, and the surrounding fourier transforms?
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