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        IplImage *img_32f = cvCreateImage(cvGetSize(img), IPL_DEPTH_32F, 1);
        cvConvertScale(img, img_32f, 1.0 / 255.0, 0);
        cvSmooth(img_32f, img_32f, CV_GAUSSIAN, 3);

        IplImage *diff_x = cvCreateImage(cvGetSize(img), IPL_DEPTH_32F, 1);
        IplImage *diff_y = cvCreateImage(cvGetSize(img), IPL_DEPTH_32F, 1);
        cvSobel(img_32f, diff_x, 1, 0, 3);
        cvSobel(img_32f, diff_y, 0, 1, 3);

        IplImage *magnitude = cvCreateImage(cvGetSize(img), IPL_DEPTH_32F, 1);
        IplImage *orientation = cvCreateImage(cvGetSize(img), IPL_DEPTH_32F, 1);
        /* calculate the edge magnitude and orientation */
        cvCartToPolar(diff_x, diff_y, magnitude, orientation, 0);