import numpy as np

def compare_neighbors(arr):
    '''
    Checks if element (i,j) is different than (i-1,j),(i+1,j),(i,j-1), or
    (i,j+1).

    --Input--
    arr: (2D np.array) array to compare all elements of

    --Returns--
    comp_arr: (2D bool np.array) bool array with the resulting comparisons.
           True means the original element is the same as its neighbors,
           False means it was different than at least neighbor
    '''
    comp_arr = np.full(arr.shape, False, dtype=bool) #initialize
    arr_width = arr.shape[0]
    arr_height = arr.shape[1]

    for i in range(arr_width): #Row
        for j in range(arr_height): #column

            #Check edges
            if i == 0: #left side
                left = arr[i,j]
            else:
                left = arr[i-1, j]

            if i == arr_width - 1: #right side
                right = arr[i,j]
            else:
                right = arr[i+1,j]

            if j == 0: #up
                up = arr[i,j]
            else:
                up = arr[i, j-1]

            if j == arr_height - 1: #down
                down = arr[i,j]
            else:
                down = arr[i, j+1]

            comp_arr[i,j] = len(set([left, right, up, down])) == 1 #compare
    return comp_arr

[[1 1]
 [1 1]]

[[ True  True]
 [ True  True]]

[[2 2]
 [2 2]]

[[ True  True]
 [ True  True]]

[[1 1 1 1 1 1 1 1 1]
 [1 1 1 1 1 1 1 1 1]
 [1 2 2 2 2 2 2 2 1]
 [1 2 2 1 1 1 2 2 1]
 [1 2 2 2 2 2 2 2 1]
 [1 1 1 1 1 1 1 1 1]]

[[ True  True  True  True  True  True  True  True  True]
 [ True False False False False False False False  True]
 [False False False False False False False False False]
 [False False False False False False False False False]
 [False False False False False False False False False]
 [ True False False False False False False False  True]]