GetChromaU        504 ext/gd/libgd/webpimg.c     *u_dst++ = GetChromaU(sum_r, sum_g, sum_b);
GetChromaU        520 ext/gd/libgd/webpimg.c     *u_dst = GetChromaU(2 * sum_r, 2 * sum_g, 2 * sum_b);