Denoising backgrounds in images

http://docs.opencv.org/trunk/d5/d69/tutorial_py_non_local_means.html

https://stackoverflow.com/questions/30369031/remove-spurious-small-islands-of-noise-in-an-image-python-opencv

https://www.mathworks.com/help/images/morphological-dilation-and-erosion.html?requestedDomain=www.mathworks.com

http://docs.opencv.org/trunk/d7/d4d/tutorial_py_thresholding.html