What Is Error Correction in a QR Code?
Direct Answer
Error correction is a built-in redundancy feature that lets a QR code still scan correctly even if part of it is dirty, damaged, or covered by a logo — the four levels (L, M, Q, H) trade off damage tolerance against data capacity.
Key Facts
- ✓Level L recovers from ~7% damage (highest capacity)
- ✓Level M recovers from ~15% damage (most common default)
- ✓Level Q recovers from ~25% damage
- ✓Level H recovers from ~30% damage (best for logo overlays)
Full Explanation
QR codes use Reed-Solomon error correction (the same family used in CDs and satellite communications) to duplicate parts of the encoded data across the grid. Higher error correction means more redundancy, so more of the code can be missing or obscured and still scan — the tradeoff is less room for actual data, which is why very long URLs sometimes need a larger printed size at higher error correction levels.
Related Questions
Can I add my logo to a QR code?
Yes, as long as the logo is small (roughly 20–25% of the code's area, centered) and the code uses a high error correction level like H, since the logo effectively covers part of the encoded data.
What happens if a QR code is damaged?
It usually still scans correctly — error correction tolerates damage ranging from about 7% (Level L) to 30% (Level H), though damage to the three corner squares is the most likely to break a scan.
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