You should find maximum matrix which is square, black and also contains white square inside rotated by 45 degrees. For instance:
1)
1 1 1 0 1 1 1
1 1 0 0 0 1 1
1 0 0 0 0 0 1
0 0 0 0 0 0 0
1 0 0 0 0 0 1
1 0 0 0 0 1 1
1 1 1 0 1 1 1
2)
1 1 1 1 0 1 1 1 1
1 1 1 0 0 0 1 1 1
1 1 0 0 0 0 0 1 1
1 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 1
1 1 0 0 0 0 0 1 1
1 1 1 0 0 0 1 1 1
1 1 1 1 0 1 1 1 1
are desired matrices maximum width of which you must find