Inverse filtering on OpenCV - accessing DFT values and multiplying DFT matrices

Question

I am trying to perform an inverse and a pseudo-inverse filtering in the frequency domain.

However I am having trouble accessing DFT coefficients and multiplying DFT matrices afterwards, since I got complex numbers and, therefore, actually two matrices...

Basically the inverse filtering performs

F = G/H,

where F is the restored image, G is the blurred image and H is the kernel that blurred the image.

The pseudo-inverse needs to access the values in H, since if the value is near 0 it should be replaced in order to avoid problems in the restoration. For this we must change the H so that:

H(u,v) = 1/H(u,v) if H(u,v) > threshold and = 0 otherwise

I have a kernel1 (h_1), and the images imf (restored) and img (blurred). Here is the code:

  // compute the DFTs of the kernel (DFT_B) and the blurred image (DBF_A)
  cvDFT( dft_A, dft_A, CV_DXT_FORWARD, complexInput1->height );
  cvDFT( dft_B, dft_B, CV_DXT_FORWARD, complexInput2->height );

  // the first type is the inverse fitlering
  if (type == 1) {
      printf("...performing inverse filtering\n");
      // dividing the transforms
      cvDiv(dft_A, dft_B, dft_C, 1);
  }
  // the second type is the pseudo-inverse filtering
  else {
      printf("...prepare kernel for pseudo-inverse filtering\n");
      // will try to access the real values in order to see if value is above a threshold
      cvSplit( dft_B, image_Re1, image_Im1, 0, 0 );
      // pointers to access the data into the real and imaginary matrices
      uchar * dRe1 = (uchar *)image_Re1->imageData;
      uchar * dIm1 = (uchar *)image_Im1->imageData;
      int width  = image_Re1->width;
      int height = image_Re1->height;
      int step = image_Re1->widthStep;
      image_Re2 = cvCreateImage(cvGetSize(image_Re1), IPL_DEPTH_32F, 1);
      image_Im2 = cvCreateImage(cvGetSize(image_Im2), IPL_DEPTH_32F, 1);
      // pointers to access the data into the real and imaginary matrices
      // it will be the resulting pseudo-inverse filter
      uchar * dRe2 = (uchar *)image_Re2->imageData;
      uchar * dIm2 = (uchar *)image_Im2->imageData;

      printf("...building kernel for pseudo-inverse filtering\n");
      for ( i = 0; i < height; i++ )  {
      for ( j = 0; j < width; j++ ) {
                // generate the 1/H(i,j) value
        if (dRe1[i * step + j] > threshold) {
            float realsq = dRe1[i * step + j]*dRe1[i * step + j];
            float imagsq = dIm1[i * step + j]*dIm1[i * step + j];

            dRe2[i * step + j] = dRe1[i * step + j] / (realsq + imagsq);
            dIm2[i * step + j] = -1 * (dIm1[i * step + j] / (realsq + imagsq));
        }
        else {
            dRe2[i * step + j] = 0;
            dIm2[i * step + j] = 0;
        }
      }
      }
      printf("...merging final kernel\n");
      cvMerge(image_Re2, image_Im2, 0, 0, dft_B);
      printf("...performing pseudo-inverse filtering\n");
      cvMulSpectrums(dft_A, dft_B, dft_C, 1);
  }
  printf("...performing IDFT\n");
  cvDFT(dft_C, dft_H, CV_DXT_INV_SCALE, 1);

  printf("...getting size\n");
  cvGetSubRect(dft_H, &tmp3, cvRect(0, 0, img->width, img->height));

  printf("......(%d, %d) - (%d, %d)\n", tmp3.cols, tmp3.rows, restored->width, restored->height);

  cvSplit( &tmp3, image_Re1, image_Im1, 0, 0 );

  cvNamedWindow("re", 0);
  cvShowImage("re", image_Re2);
  cvWaitKey(0);

  printf("...copying final image\n");
  // error is in the line below
  cvCopy(image_Re1, imf, NULL);

I have an error on the last line: --- OpenCV Error: Assertion failed (src.depth() == dst.depth() && src.size() == dst.size()) in cvCopy, file /build/buildd/opencv-2.1.0/src/cxcore/cxcopy.cpp, line 466

I know it have to do with the size or depth but I don't know how to control. Anyway, I tried to show the image_Re1 and it is empty...

Can anyone shed some light on it?

Try and reduce the above code to a minimal example which still exhibits the problem - you're much more likely to get an answer that way. — Paul R

Deadolus Deadolus · Accepted Answer · 2011-10-21T15:25:07

Seems like you didn't initialize your imf picture! cvCopy needs a initialized matrix do a:

IplImage* imf=   cvCreateImage(cvGetSize(image_Re1), IPL_DEPTH_32F, 1);

first and I think it'll work.

Also, you don't free the image space in this code (cvReleaseImage(&image))

Inverse filtering on OpenCV - accessing DFT values and multiplying DFT matrices

1 Answers