OpenCV-remap（）-获得黑色像素

Question

I'm using an STMap to map a .jpg image using remap() .

I loaded my STMap, split the channels and converted each channel matrix to CV_32FC1 . I checked them and it worked - each matrix displays correctly and all of its values are between 0.0 and 1.0.

However, when i try to use the remap() function:

Mat dst;
remap(image4, dst,map_x,map_y,INTER_LINEAR,BORDER_CONSTANT,Scalar(0,0,0));
imshow( "Result", dst );

It just displays a black image.

1. image4 = my .jpg image
2. map_x = grayscale CV_32FC1 (red channel of the original STMap)
3. map_y = grayscale CV_32FC1 (green channel of the original STMap)

What could be the problem?

Thanks!

Answer 1

Black image when using cv::remap is due to using offsets instead of absolute locations in the passed map(s).

Optical flow algorithms usually export motion vectors, not absolute positions, whereas cv::remap expects the absolute coordinate (subpixel) to sample from.

To convert between the two, starting with a CV_32FC2 flow matrix we can do something like this:

// Convert from offsets to absolute locations.
Mat mapx(flow.size(), CV_32FC1);
Mat mapy(flow.size(), CV_32FC1);
for (int row = 0; row < flow.rows; row++)
{
  for (int col = 0; col < flow.cols; col++)
  {
    Point2f f = flow.at<Point2f>(row, col);
    mapx.at<float>(row, col) = col + f.x;
    mapy.at<float>(row, col) = row + f.y;
  }
}

Then mapx and mapy can be used in remap .