## OpenCV CalcOpticalFlowHS Horn-Schunck

The default `lambda=1.0`

smoothness parameter for
OpenCV 2.4 `CalcOpticalFlowHS`

does not work well for some cases.
Also, OpenCV’s `lambda`

is different from
Matlab Computer Vision Toolbox Horn Schunck
`opticalFlowHS('Smoothness',1.0)`

parameter, which also defaults to `1.0`

.

Horn Schunck Optical Flow comparison between Matlab and Python
OpticalFlow_Python_vs_Matlab.py shows that OpenCV `CalcOpticalFlowHS`

setting `lambda=0.001`

gives results that are much more like Matlab.
OpenCV no longer has the original Horn Schunck optical flow.

Linearized Horn Schunck has problems with large displacements in the image, which can be resolved by a pyramidal algorithm.