Looping over averages in an int[][] array

I need no add an average to ever member in this int[][] array without using about 256 lines of code to replace it. I am adveraging the height of a grid of squares like this:
[a][b][c][d][e] with c being the average of a and e, and b being the average of a and c, and so on. It gets more complicated though:
[a][b][c][d][e]
[f] [g][h][i] [j]
[k] [l][m][n][o]
[p][q][r] [s] [t]
[v][w][x][y][z] (don't yell that I missed "u"!)
So h is the average of m and c, and i is the average of c, e, m and o. This has to be done for a 16² grid.

I think that I speak for all in wishing you much success in this assignment.

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