Local Mean and Variance

I have an artificial flow field given by a homography transform. I want to compare this flow field to the results of an optical flow algorithm. I want to do a pixel-wise comparison in a statistical manner. It seems to me that I can best do this by comparing the optical flow value to the statistics of the local neighborhood of the homography flow. See [this paper](https://www.researchgate.net/profile/Thomas_Castelli3/publication/283462638_Moving_object_detection_for_unconstrained_low-altitude_aerial_videos_a_pose-independant_detector_based_on_Artificial_Flow/links/56390bb208aecf1d92a9bc69.pdf) for inspiration. My question is, what OpenCV functions can I use to calculate the local mean and variance over some window?