gistfile1.txt

$ python3.4
Python 3.4.0 (default, Jun 19 2015, 14:20:21) 
[GCC 4.8.2] on linux

>>> import numpy
>>> a = numpy.array([[[127, 127, 127, 255],
...                   [127, 127, 127, 255]],
...                  [[127, 127, 127, 255],
...                   [127, 127, 127, 255]]])

>>> b = numpy.array([[[127, 127, 127, 255],
...                   [255, 0,   0,   255]],
...                  [[0,   255, 0,   255],
...                   [0,   0,   255, 255]]])

>>> ((a - b) + 255)/2
array([[[ 127.5,  127.5,  127.5,  127.5],
        [  63.5,  191. ,  191. ,  127.5]],

       [[ 191. ,   63.5,  191. ,  127.5],
        [ 191. ,  191. ,   63.5,  127.5]]])




I would like this instead
array([[[ 127,  127,  127,  127],
        [  63,  191,  191,  127]],

       [[ 191,   63,  191,  127],
        [ 191,  191,   63,  127]]])