get_velocities fails for non-Farneback algorithms because _get_velocities is None

[hrehmaan]

Hello Henrik

I noticed that mps_motion.list_optical_flow_algorithm() reports the following algorithms:

['farneback', 'dualtvl1', 'lucas_kanade', 'block_matching']

However, when I try to use get_velocities() with algorithms other than farneback, it fails because _get_velocities is None.

Than I tested

import mps
import mps_motion

data = mps.MPS("Control_1.czi", channel=1)

for alg in mps_motion.list_optical_flow_algorithm():
    opt_flow = mps_motion.OpticalFlow(data, flow_algorithm=alg)
    print("\nAlgorithm:", alg)
    print("_get_velocities:", opt_flow._get_velocities)
    print("callable:", callable(opt_flow._get_velocities))

and the output of it
Algorithm: farneback
_get_velocities: <function get_velocities at 0x1245656c0>
callable: True

Algorithm: dualtvl1
_get_velocities: None
callable: False

Algorithm: lucas_kanade
_get_velocities: None
callable: False

Algorithm: block_matching
_get_velocities: None
callable: False

[finsberg]

Thanks for reporting @hrehmaan. This is because I have implemented it for farneback (see here). It shouldn't be too difficult to implement this for the other methods (but I found farneback methods to give the best results for the cases I tested).