image preprocessing

[dalessioluca]

check:

1. https://arxiv.org/abs/1812.10366
2. http://bigwww.epfl.ch/algorithms/denoise/

[dalessioluca]

This is related to issue #7

[dalessioluca]

Do Otsu on the image and add a cross entropy loss between fg_mask and otsu_mask this can be simply added as a regularization in the dictionary

[dalessioluca]

Since I am going to use a non-physical log-likelihood (i.e. it is not the correct poisson-gaussian model) then I am allowed to do non-linear transformations to enhance the image.

I have found out that:

1. remove background with otsu
2. rescale fg_intensity in (0,1) (this is linear transformation)
3. use adaptive_hist_equalization to enhance local contrast.
   tmp_MAIN.pdf

[dalessioluca]

in pull request #29 preprocessing has been fixed