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A miniature about scanning

The Code That Expects Dirt

A QR code keeps three anchors for orientation and adds recovery data for errors. Turn it, stain it, and see what remains readable.

3position anchors
4recovery levels
1message to scan
Enter the mechanism

The image is a real QR code for this page. When you start the interactions, the colored accents become explanatory layers.

QR / H / 33 × 33mariuscomper.uk/codul-qr/

01 · orientation

Three squares tell a scanner where the code is

A scanner has to find the code and read its angle. The three position patterns sit in the corners. Their width ratio is 1:1:3:1:1, a rare signature in printed material.

Documented fact · DENSO WAVE
anchor width ratio
1:1:3:1:1

02 · reserve

A QR code pre-pays for some of its mistakes

When you generate it, you choose how much space to allocate to recovery data. The code uses Reed–Solomon, a method that corrects errors at byte level. More reserve means less room for the message at the same code version.

Documented fact · DENSO WAVE / ISO/IEC 18004
Choose the recovery level

The percentages refer to total codewords, with 8 bits in each codeword.

explanatory reserveH · 30%

03 · damage

Erased area is not the only measure of loss

Move the slider and change the damage shape. A compact stain and a scratch across the code can cover the same area while touching different byte groups. The model turns that distinction into a visual intuition; a real phone also depends on contrast, size, distance, and printing.

Visual inference · official percentages are calculated on codewords, not individual squares.
0% of model
Damage shape

The code is intact. Its message and anchors are visible.

Visual inference · official percentages are calculated on codewords, not individual squares.

What remains

Every square carries two instructions

The first carries a message. The second helps a scanner find that message and recover part of it when the ink gets dirty. The result is a small object built for an imperfect world.

Keep the idea: when you see a QR code, look for the hidden reserve that makes it useful in the real world.

Sources and limits

What is documented and what is a model

This page uses the format’s official documentation and a visual reconstruction to make the mechanism easy to see.

The damage state is a teaching model. It keeps the matrix of a real QR code and makes the idea of reserve visible; it does not replace a scan test under controlled conditions.

Status: evergreen, periodically reviewed. Review is triggered by a material change to ISO/IEC 18004 or the official definitions of recovery levels.

Evidence checked on 12 August 2026.