Find the submatrix with the smallest mean You're given a n-by-m matrix of integers, where n,m > 3. Your task is to find the 3-by-3 sub-matrix that has the lowest mean, and output this value.

Rules and clarifications:


The integers will be non-negative
Optional input and output format
The output must be accurate up to at least 2 decimal poins (if it's non-integer)
The submatrices must be made up of consecutive rows and columns


Test cases:

35    1    6   26   19   24
 3   32    7   21   23   25
31    9    2   22   27   20
 8   28   33   17   10   15
30    5   34   12   14   16
 4   36   29   13   18   11 

Minimum mean: 14




100    65     2    93
  3    11    31    89
 93    15    95    65
 77    96    72    34

Minimum mean: 46.111




1   1   1   1   1   1   1   1
1   1   1   1   1   1   1   1
1   1   1   1   1   1   1   1
1   1   1   1   1   1   1   1

Minimum mean: 1




4   0   0   5   4
4   5   8   4   1
1   4   9   3   1
0   0   1   3   9
0   3   2   4   8
4   9   5   9   6
1   8   7   2   7
2   1   3   7   9

Minimum mean: 2.2222


This is code-golf so the shortest code in each language wins. I encourage people to post answers in languages that are already used, even if it's not shorter than the first one.
Octave, 30 bytes
@(A)min(mean(im2col(A,[3,3])))

Try it online!