void sum1(unsigned char *a, const unsigned char *b, const unsigned char *c, int h, int w, int rb)
{
    typedef unsigned char imgrow[rb];
    typedef imgrow img[h];
    img *ar = (img *)a;
    const img *br = (const img *)b;
    const img *cr = (const img *)c;

    for (int y = 0; y < h; y++)
        for (int x = 0; x < w; x++)
            (*ar)[y][x] = (*br)[y][x] * (*cr)[y][x];
}