Definition
Error correction is the mechanism that keeps a QR code readable even when it is partially damaged, dirty or covered. It relies on the Reed-Solomon algorithm, which encodes redundant data so the reader can reconstruct what is missing. QR codes offer four levels — L (~7%), M (~15%), Q (~25%) and H (~30%) of recoverable loss — trading density for robustness. For designers this margin is what makes it possible to place a logo at the center or stylize the pattern without breaking the scan.
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