float convolve(mat3x3 kernel, mat3x3 sample){
    float accumulator = 0, sum = 0;
    for(int r = -1; r < 2; r++){
        for(int c = -1; c < 2; c++){
            sum += kernel[r + 1][c + 1];
            accumulator += kernel[r + 1][c + 1] * sample[-r + 1][-c + 1];
        }
    }
    return accumulator;// / sum;
}