OpenCV, How to pass parameters into cv2.TrackerMedianFlow_create function? - python-3.x

Question

I'm trying to create MEDIANFLOW tracker with OpenCV3.3 using opencv-python with Python3.6. I need to pass some arguments into the constructor according to this page of OpenCV docs.
The problem is I don't know how to pass available arguments into this function correctly? I wasn't able to find any information about it.
What I do (and it works):
tracker = cv2.TrackerMedianFlow_create()
What I want to do:
tracker = cv2.TrackerMedianFlow_create(maxLevel=3)
But it doesn't work and gives me an error:
SystemError: <built-in function TrackerMedianFlow_create> returned NULL without setting an error
Could you help?

Answer 1

I search the intermediate code generated by cmake/make when compiling the OpenCV 3.3 for Python 3.5, just cannot find the methods to set the parameters for cv2.TrackerXXX.
In modules/python3/pyopencv_generated_funcs.h, I find this function:
static PyObject* pyopencv_cv_TrackerMedianFlow_create(PyObject* , PyObject* args, PyObject* kw)
{
using namespace cv;
Ptr<TrackerMedianFlow> retval;
if(PyObject_Size(args) == 0 && (kw == NULL || PyObject_Size(kw) == 0))
{
ERRWRAP2(retval = cv::TrackerMedianFlow::create());
return pyopencv_from(retval);
}
return NULL;
}
This is to say, you cann't pass any parameter to cv::TrackerMedianFlow_create().
In modules/python3/pyopencv_generated_types.h, I find this one:
static PyGetSetDef pyopencv_TrackerMedianFlow_getseters[] =
{
{NULL} /* Sentinel */
};
This to say, you have no way to change the parameters for Python wrapper by default, Unless you modified the source code and recompile it.

Answer 2

You can customize Tracker parameters via FileStorage interface.
import cv2
# write
tracker = cv2.TrackerMedianFlow_create()
tracker.save('params.json')
# write (another way)
fs = cv2.FileStorage("params.json", cv2.FileStorage_WRITE)
tracker.write(fs)
fs.release()
# read
tracker2 = cv2.TrackerMedianFlow_create()
fs = cv2.FileStorage("params.json", cv2.FileStorage_READ)
tracker2.read(fs.getFirstTopLevelNode())