QR Code Error Correction
QR Codes use Reed-Solomon error correction, which adds redundant data so codes can still scan even when partially damaged, dirty or covered by a logo.
The four levels
Level L: 7% recovery. Level M: 15% recovery. Level Q: 25% recovery. Level H: 30% recovery. Higher levels create denser codes but tolerate more damage.
When to use each level
Use L for clean, indoor environments. Use M for general purpose (recommended). Use Q or H for outdoor signage, industrial use or codes with centred logos.
Why logos work
A centred logo covers part of the data modules. Error correction fills in the gaps so the code still scans. Keep logos under 20% of the code area for reliable scanning.