GetChromaV        505 ext/gd/libgd/webpimg.c     *v_dst++ = GetChromaV(sum_r, sum_g, sum_b);
GetChromaV        521 ext/gd/libgd/webpimg.c     *v_dst = GetChromaV(2 * sum_r, 2 * sum_g, 2 * sum_b);