ArUco Decoding Details

This chapter expands on the marker decoding path in calib-targets-aruco. The decoder is grid-first: it samples expected square cells and reads bits in rectified space (or per-cell quads).

When to use per-cell decoding

Use per-cell decoding (scan_decode_markers_in_cells) when you already have a grid of square corners and want to avoid warping the full image. It works well with ChArUco detection because you can decode only the valid cells and parallelize across them.

Sampling model

• Bits are sampled on a regular grid inside the marker area.
• The marker area is defined by marker_size_rel, with an extra inset from inset_frac.
• A per-marker threshold (Otsu) is computed from sampled intensities.

Tuning checklist

• If markers are missing, try reducing inset_frac slightly.
• If false positives appear, raise min_border_score or enable dedup_by_id.
• Make sure marker_size_rel matches the physical board spec.