width>>=1;
static void conv411(uint8_t *dst, int dst_wrap,                     uint8_t *src, int src_wrap,                    int width, int height){    int w, c;    uint8_t *s1, *s2, *d;    for(;height > 0; height--) {        s1 = src;        s2 = src + src_wrap;        d = dst;        for(w = width;w > 0; w--) {            c = (s1[0] + s2[0]) >> 1;            d[0] = c;            d[1] = c;            s1++;            s2++;            d += 2;        }        src += src_wrap * 2;        dst += dst_wrap;    }}