Are you wanting to reflect the edge values like the following numpy example? and if so, how far inwards do you want to reflect/mirror?
>>> import numpy as np
>>> a = np.array([[1,1,1],[1,0,1],[1,1,1]])
>>> a
array([[1, 1, 1],
[1, 0, 1],
[1, 1, 1]])
>>> np.pad(a,1,mode="edge")
array([[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 0, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1]])
>>>
Perhaps a better illustration
- set all the cells within 2 cells of the boundary to 0
- pad the raster by mirroring the edge by 2 cells
>>> c = np.arange(100,dtype='int32').reshape((10,10))
>>> c
array([[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19],
[20, 21, 22, 23, 24, 25, 26, 27, 28, 29],
[30, 31, 32, 33, 34, 35, 36, 37, 38, 39],
[40, 41, 42, 43, 44, 45, 46, 47, 48, 49],
[50, 51, 52, 53, 54, 55, 56, 57, 58, 59],
[60, 61, 62, 63, 64, 65, 66, 67, 68, 69],
[70, 71, 72, 73, 74, 75, 76, 77, 78, 79],
[80, 81, 82, 83, 84, 85, 86, 87, 88, 89],
[90, 91, 92, 93, 94, 95, 96, 97, 98, 99]])
>>> c[2:8,2:8] = 0
>>> c
array([[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19],
[20, 21, 0, 0, 0, 0, 0, 0, 28, 29],
[30, 31, 0, 0, 0, 0, 0, 0, 38, 39],
[40, 41, 0, 0, 0, 0, 0, 0, 48, 49],
[50, 51, 0, 0, 0, 0, 0, 0, 58, 59],
[60, 61, 0, 0, 0, 0, 0, 0, 68, 69],
[70, 71, 0, 0, 0, 0, 0, 0, 78, 79],
[80, 81, 82, 83, 84, 85, 86, 87, 88, 89],
[90, 91, 92, 93, 94, 95, 96, 97, 98, 99]])
>>> d = np.pad(c,2,mode='edge')
>>> d
array([[ 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9, 9],
[ 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9, 9],
[ 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9, 9],
[10, 10, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 19, 19],
[20, 20, 20, 21, 0, 0, 0, 0, 0, 0, 28, 29, 29, 29],
[30, 30, 30, 31, 0, 0, 0, 0, 0, 0, 38, 39, 39, 39],
[40, 40, 40, 41, 0, 0, 0, 0, 0, 0, 48, 49, 49, 49],
[50, 50, 50, 51, 0, 0, 0, 0, 0, 0, 58, 59, 59, 59],
[60, 60, 60, 61, 0, 0, 0, 0, 0, 0, 68, 69, 69, 69],
[70, 70, 70, 71, 0, 0, 0, 0, 0, 0, 78, 79, 79, 79],
[80, 80, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 89, 89],
[90, 90, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99, 99],
[90, 90, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99, 99],
[90, 90, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99, 99]])
>>> import arcpy
>>> raster = arcpy.NumPyArrayToRaster(d)
>>> raster.save("f:/temp/raster.tif")
with some random color scheme