Optimize the loop @ c++

I WANT THIS LOOP to RUN FASTER than now , do whatever optimizations u need

int a = filter -> getDivisor();

int n = filter -> getSize();

for(int row = 1; row < (input -> height) - 1 ; row = row + 1) {

for(int col = 1; col < (input -> width) - 1; col = col + 1) {

int value = 0;

for (int plane = 0; plane < 3; plane++){

for (int j = 0; j < n; j++) {

for (int i = 0; i < n; i++) {

value = value + input -> color[plane][row + i - 1][col + j - 1]

* filter -> get(i, j);

}

value = value / a;

if ( value < 0 ) { value = 0; }

if ( value > 255 ) { value = 255; }

output -> color[plane][row][col] = value;

}

Cheers

Thank you