// Count the number of Alive pixels around the pixel at (x, y).
int countNeighbours(CImg<unsigned char> &image, int x, int y)
{
    int count = 0;
    for (int x0 = x -1; x0 < x + 2; x0++)
    {
        if (x < 0 || x >= image.width())
            continue; // Skip this loop if out of range.
        for (int y0 = y -1; y0 < y +2; y0++)
        {
            if (y < 0 || y >= image.height())
                continue; // Skip this loop if out of range.

            if(!(x0 == x && y0 == y))
            { // Check we're not on current pixel.
                count += image(x0, y0, 0);
            }
        }
    }
    // Count number of living around pixel and return.
    // Divide by 255 because each time we increment count using image(x,y,0)
    // if it is white the number returned will be 255.
    // Do 8 - (ans) because white = dead.
    return(8 - (count/255));
}