How can i subtract the background from an image in mahotas and opencv in python?

Question

I have many image like this or like this and i use this code:

fork = mh.imread(path)
bin = fork[:,:,0]
bin = mh.erode(bin)
bin = (bin < 80)

for the 2nd image, but i have to use this:

bin = (bin < 127)

for the first.

There is a way for automatically obtain a good image without background, or i have to choose a median value hopefully is good for the most of my images?

Answer 1

There is a threshold value that is called "Otsu Threshold". Here you have more information.

You can use otsu to do it in Mahotas or threshold_otsu in scikit-image:

fork = mh.imread(path)
bin = fork[:,:,0]
thresh = mh.otsu(bin)
binary =( bin< thresh)