十万个为什么·科学启蒙30篇（4）
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How QR Codes Tolerate Damage
为什么二维码能容错一部分污损
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QR codes use Reed–Solomon error correction, which adds extra data to reconstruct missing parts.
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They divide information into modules and encode redundancy so damaged sections can be guessed accurately.
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Four levels of error correction exist: L (7%), M (15%), Q (25%), and H (30%)—higher levels mean more resilience.
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A scuffed corner or coffee stain may remove up to 30% of modules without breaking the code’s readability.
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Scanners detect alignment patterns and timing grids first, then decode the message using mathematical recovery rules.
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This built-in redundancy lets QR codes work even when printed on curved or worn surfaces like packaging or posters.
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Unlike barcodes, which store data linearly, QR codes hold information in two dimensions—making them far more robust.
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Designers choose error level based on expected use: high-risk environments need H-level protection.