static unsigned char grid_21_bits[] = {
   0x00, 0x00, 0x00, 0x10, 0x11, 0x01, 0xfe, 0xff, 0x0f, 0x10, 0x11, 0x01,
   0x10, 0x11, 0x01, 0x10, 0x11, 0x01, 0xfe, 0xff, 0x0f, 0x10, 0x11, 0x01,
   0x10, 0x11, 0x01, 0x10, 0x11, 0x01, 0xfe, 0xff, 0x0f, 0x10, 0x11, 0x01,
   0x10, 0x11, 0x01, 0x10, 0x11, 0x01, 0xfe, 0xff, 0x0f, 0x10, 0x11, 0x01,
   0x10, 0x11, 0x01, 0x10, 0x11, 0x01, 0xfe, 0xff, 0x0f, 0x10, 0x11, 0x01,
   0x00, 0x00, 0x00};