The phobos image contains three neighbouring columns, which are
    brighter than their surroundings. Find them and correct them by
    scaling them with an approprate factor. 
Create and plot a large image made up of the following four
    images:
- -
 - phobos with bad spots, 
     
 - -
 - bad spots,
     
 - -
 - phobos without bad spots,
     
 - -
 - phobos with corrected line.
   
 
Start with the original image.