7x7_50
7x7_50 holds 50 markers of
7×7 bits. In OpenCV it is
cv2.aruco.DICT_7X7_50.
The numbers
| OpenCV name | cv2.aruco.DICT_7X7_50 |
| Bits in a marker | 7 × 7 = 49 |
| Markers available | 50, with IDs 0 to 49 |
| Printed width | 9 cells, border included |
| Bits the decoder repairs | 9 |
| Cell size on a 100 mm marker | 11.1 mm |
| Pixels wanted in the image | 108 (floor 36) |
| Range for a 100 mm marker | about 1.5 m |
Range assumes a camera 1920 px wide, 60 degree horizontal field of view, which is a focal length of about 1663 pixels, and a marker seen straight on.
When to use it
Seven bit markers hold the most information and repair the most damage, but their cells are the smallest, so they need the closest camera or the largest print. With 50 markers this suits a single board or a small set of tagged objects.