How Do I Solve Here Chanel?

for (k=0; k < 4; k++)
{
   roi_out1 = roi_array[g] + roi_array[g + 1] + roi_array[g + 2];
   imshow("Accumulator", roi_out1);
}
int m = getOptimalDFTSize(roi_out1.rows);
int n = getOptimalDFTSize(roi_out1.cols);
// on the border add zero values
copyMakeBorder(roi_out1, padded, 0, m - roi_out1.rows, 0, n - roi_out1.cols, BORDER_CONSTANT, Scalar::all(0));

Mat planes[] = {Mat_<float>(padded), Mat::zeros(padded.size(), CV_32F)};

Mat complexroi_out1;
merge(planes, 2, complexroi_out1);          // Add to the expanded another plane with zeros

dft(complexroi_out1, complexroi_out1);      // this way the result may fit in the source matrix

split(complexroi_out1, planes);             // planes[0] = Re(DFT(I), planes[1] = Im(DFT(I))
magnitude(planes[0], planes[1], planes[0]); // planes[0] = magnitude
Mat roi_out1 = planes[0];