# -*- coding: utf-8 -*-
"""
Created on Fri Jan 27 11:30:12 2017

@author: khsk
"""

import numpy as np
import cv2 as c
import glob
import os

#8 Definition of neighborhood
neiborhood8 = np.array([[1, 1, 1],
                            [1, 1, 1],
                            [1, 1, 1]],
                            np.uint8)

for path in glob.glob('./images/eupho/*'):
    if (os.path.basename(path) == 'Thumbs.db'):
        continue
    img = c.imread(path, 0) #Color without 0
    img_dilate = c.dilate(img, neiborhood8, iterations=1)
    img_diff = c.absdiff(img, img_dilate)
    img_diff_not = c.bitwise_not(img_diff)
    #gray = c.cvtColor(img_diff_not, c.COLOR_RGB2GRAY)
    
    #at = c.adaptiveThreshold(img_diff_not, 255, c.ADAPTIVE_THRESH_GAUSSIAN_C, c.THRESH_BINARY, 7, 8) #Adjust int nicely
    c.imwrite(os.path.dirname(path) + '_clean_senga_color_gray/' + os.path.basename(path), img_diff_not)
    
c.imshow('test',img)
c.imshow('test2',img_dilate)
c.imshow('test3',img_diff)
c.imshow('test4',img_diff_not)
c.waitKey(10000)

c.destroyAllWindows()

Basic code. Comment out, change variables, and mess with int values. There seems to be an expansion of around 4, but if you want to make it clearer, I thought it might be around 8 more. However, unless otherwise stated, reading is in grayscale.

</ i> Original image