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What is QR code error recovery

Error recovery in QR codes allows pieces of information in the QR code to be damaged or missing and still have the ability to be read correctly. In a nutshell, it does this by using some very clever complex algorithms to place 'compressed duplicated' information in different places of the QR code, so if some data goes missing it can (try too) reconstruct the missing pieces using the remainder of the existing code.

There are four different settings available that can be chosen from before creating the QR code, Each one allows for a different amount of data loss.

QR Code Error Correction 7% QR Code Error Correction 15% QR Code Error Correction 25% QR Code Error Correction 30%
 7% Loss Recovery  15% Loss recovery  25% Loss Recovery  30% Loss Recovery

So why not always make QR codes that support 30% loss recovery?

The higher the damage recovery percentage, the more room is needed inside the QR code to encode and store the information vital to recovery. Below is a URL QR code of the same URL and created using the four different error compensation selections.

QR Code using 7% Error Correction QR Code using 15% Error Correction QR Code using 25% Error Correction QR Code using 30% Error Correction
 7% fault tolerant  15% fault tolerant  25% fault tolerant  30% fault tolerant

Scan any of the four codes and they will all take you the same URL. the left QR code is more sensitive to damage then right one. Lets put this to the test by taking the first and the last QR code and 'damaging' them proportionately in favor of the smaller QR code.

Non Readable Damaged QR Code Readable Damaged QR Code
 Bad QR code  QR code still readable

Clearly the 30% fault tolerant QR code on the right still scans even though a big piece of its data has been obscured, while the smaller code on the left no longer works at all, even though visually it has less data damage.

This same technique is used to create designer QR codes. Making QR codes pretty by damaging the data but at the same time keeping them scannable and working.

How to use QR code error recovery

When creating QR codes for example business cards, the chances of it getting dirty are rather low and you want the QR code as small as possible. Here a standard 7% error threshold is enough and very suitable for cards and other printed matter. However if are going to use QR codes outdoors, on cars and trucks or any place where data may be obscured by dirt then setting the error correction to a higher setting is advisable although chances are you will land up with a bigger image.

TIP: Do not believe everything people tell you about QR codes...ask them to prove it and show you!
Myth: 'you can tear a QR code in half and it can still be read'
Here's what a British 'technology consultant' had to say during an interview on business hub radio...

Should you have any questions or need professional advise QR code use and strategy, please contact us.

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Posted by: jeroen Steeman
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Categories: QR Code Error Correction | QR Codes
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