Recovery codewords add resilience
Reed-Solomon recovery can reconstruct some damaged codewords. It does not preserve a second visible copy of every missing square.
Episode V002 · Source record
How a Damaged QR Code Can Still Scan
QR Code adds recovery codewords to the encoded data. In one fixed Version 3 test, a Level H symbol returned its exact harmless text after an 11 by 11 center block was removed. Move the same-size block over a finder region and both selected decoders reported no detection.
- Research lock
- August 8, 2026
- Evidence stack
- 14 source records · 14 direct links
- Visual proof
- Original deterministic decoder model
FIXED VERSION 3 TEST · HARMLESS PLAIN TEXT
SAME GAP. DIFFERENT RESULT.
LOCATION CAN MATTER · NOT A UNIVERSAL TOLERANCE
The sourced answer
Recovery begins only after the symbol can be found and sampled.
Detection comes first
A reader must locate, orient, and sample the grid before correction can recover the payload. Damage to a finder region can prevent that earlier stage.
Thirty percent is not a cutout rule
The familiar Level H figure describes approximate codeword restoration, not permission to remove thirty percent of any visible area.
Original QR damage model
One payload. Four correction levels. Five controlled gaps.
The model generated every symbol locally with the plain-text payload HIDDEN LOGIC V002 TEST PAYLOAD. It then applied module-aligned white squares and decoded every saved case.
Deterministic digital test. Not a universal scanner rating.
- 7 by 7 center: L failed; M, Q, and H passed
- 9 by 9 center: L and M failed; Q and H passed
- 11 by 11 center: only H passed
- 13 by 13 center: every selected level failed
- 11 by 11 finder-region gap: Level H was not detected
All clean controls returned the exact payload. zxing-cpp and Apple Vision agreed on the selected center-pass, finder-fail, and larger-center-fail outcomes.
Equal-area location test
The same missing square did not produce the same result.
Center
The Level H symbol with an 11 by 11 center block returned the exact fixed plain-text payload in both selected decoders.
Finder region
Move the same block over the top-left finder region and neither selected decoder detected a symbol.
Narrow conclusion
Damage location can matter because detection, format reading, sampling, and codeword recovery are different jobs. The model does not rank every possible location.
Direct source library
Trace every public claim.
Each note states what its reference supports and where the evidence stops. External sources open in a new tab.
Standard and mechanism
Recovery works on codewords, not arbitrary visible area
These public records support the QR Code scope, selectable correction levels, Reed-Solomon recovery, symbol versions, and reading conditions.
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ISO/IEC 18004:2024
International Organization for Standardization
The public record identifies the fourth edition of the QR Code symbology specification and its broad scope. The paid normative text is not quoted or reproduced.
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QR Code Standardization
DENSO WAVE
The page lists L, M, Q, and H as selectable correction levels with approximate codeword restoration figures. Those figures are not guarantees for the same percentage of visible square area.
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Error Correction Feature
DENSO WAVE
The page describes Reed-Solomon recovery code added to the original data, byte-level correction, and the capacity tradeoff created by stronger correction.
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What Is a QR Code?
DENSO WAVE
This overview describes codewords, the three corner position patterns, and the fact that restoration can still fail depending on damage conditions.
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Information Capacity and Versions
DENSO WAVE
The page establishes the Version 1 through Version 40 size progression. The original V002 test uses only Version 3 at 29 by 29 modules.
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Point for Determining the Code Area
DENSO WAVE
The page describes the four-module quiet zone around a standard QR Code. One clean digital test is not production guidance for cropped or printed symbols.
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Point for Setting the Module Size
DENSO WAVE
The page explains why usable physical size depends on printing and reader resolution. V002 does not claim a universal phone-camera result.
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QR Code FAQ
DENSO WAVE
The FAQ supplies the trademark and editorial-use boundary. This page does not reproduce publisher figures, logos, interfaces, or trade dress.
Implementation evidence
Detection and recovery are separate stages
The selected zxing-cpp 3.1.1 files show one implementation path from detection through parsing, block construction, and Reed-Solomon decoding. They are not the source code inside every reader.
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QRDetector.cpp, version 3.1.1
zxing-cpp contributors
The detector source supports the bounded explanation that a reader first has to locate and sample a plausible symbol before payload recovery can succeed.
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QRBitMatrixParser.cpp, version 3.1.1
zxing-cpp contributors
The parser source provides implementation evidence for reading format and mask information and extracting symbol codewords.
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QRDecoder.cpp, version 3.1.1
zxing-cpp contributors
The decoder source supplies implementation evidence for Reed-Solomon correction and subsequent payload interpretation.
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QRDataBlock.cpp, version 3.1.1
zxing-cpp contributors
The data-block source supports the explanation that data and correction codewords are distributed through blocks rather than mapped as one duplicate visible picture.
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QREncoder.cpp, version 3.1.1
zxing-cpp contributors
The encoder source shows one implementation adding recovery bytes, interleaving codewords, and selecting a mask. It is not claimed as every encoder's implementation.
Safety boundary
Recovery does not make a destination trustworthy
A technically successful scan can still return a deceptive or harmful destination. V002 uses harmless plain text and performs no network action.
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Scammers Hide Harmful Links in QR Codes
U.S. Federal Trade Commission
The FTC warns that a QR Code can lead to a spoofed site or malware and recommends checking the destination. This safety note does not alter the engineering result.