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Data matrix codes on a Royal Mail Smart Stamp letter.

QR codes and 2D barcodes

by Chris Woodford. Last updated: September 8, 2013.

From buying groceries to tracking a UPS delivery, barcodes make our lives easier in all kinds of ways—but they've been doing so now for decades. Originally patented in the 1940s, barcodes were commercially tested in the 1960s and gradually became ubiquitous in the 1980s. The basic idea has barely changed in all that time: just like in the 1960s, a barcode is still a zebra pattern of stripes with numbers written underneath that needs a special scanning device to decode it. But all that could change soon as the 2D barcode—a kind of second-generation barcode technology—slowly takes over. Let's take a closer look at how it works!

Photo: Do-it-yourself postal systems, such as Royal Mail's SmartStamp® (in the UK) and Deutsche Post's Stampit (in Germany), let you print your own franking labels on parcels without the bother of going to a post office. They print a 2D barcode on the postage label to validate it and protect against fraud. The code is read and checked when the mail passes through automated sorting equipment. This is an example of a data-matrix code made from four separate segments.

What are 2D barcodes?

Example of a QR code being used to good effect on a promotional marketing leaflet.

You might have already noticed odd black-and-white squares appearing on your parcels, letters, utility bills, T-shirts, product packaging, and in all kinds of other places— a bit like mini crossword puzzles without any letters. They're called two-dimensional (2D) barcodes and, just like ordinary barcodes, they're machine-readable so they can quickly pass on information about a product in the blink of an electronic eye. Where a barcode presents a string of information as a one-dimensional line of black and white bars, a 2D barcode packs a lot more information into a grid of black and white, square-shaped dots.

Photo: It's a great idea to turn your website address (URL) into a QR Code® and put it on all your promotional material—from advertisments and leaflets to T-shirts and delivery vans. Here's a QR Code being used to good effect on a promotional leaflet from the Swanage Railway. If I want to find out more, all I have to do is point my cellphone at the leaflet and click. Be careful how you print the code: although there's some tolerance for bad printing, it still needs to be printed reasonably clearly and accurately or it won't work. So crisp laser printing is fine, but smudgy inkjet prints probably aren't. Always test the final, printed code with a QR Code reader to make sure it takes you where it should!

What are the advantages of 2D barcodes?

If we already have barcodes, why do need something else as well? 2D barcodes are a step further, with lots of advantages:

What are the different kinds of 2D barcode technology?

To an untrained eye, 2D barcodes all look much the same. Look more closely, though, and you'll see they do vary quite a bit. There are actually several different types of 2D barcode, some available in the public domain and some that are still proprietary. The best known include QR Code® (pioneered in the 1990s by Japanese company Denso-Wave), Aztec code (developed by Welch Allyn and recognizable by a distinctive square "bulls-eye" pattern in the center), MaxiCode (used by the US postal service, and featuring a round "bulls-eye" center), and Semacode—though there are literally dozens of others. Data-matrix code is the name of the international (ISO) standards covering 2D barcodes, but not all 2D barcodes comply with them (Semacode does; QR codes and Aztec codes are slightly different).

Example of a QR code for explainthatstuff.com. Example of an Aztec code for explainthatstuff.com.
Photo: Two examples of 2D barcodes: A QR Code on the left and an Aztec code on the right. Both contain the address of this website (www.explainthatstuff.com), but look how very different they are: there are many different ways of encoding the same basic informatin in a 2D data matrix pattern.

What information does a QR code contain?

By their very nature, QR codes (and other data matrix codes) are meant to be read by machines, not humans, so there's only a certain amount we can tell just by looking at them. Although each code is different, they contain a few interesting, common features. Looking again at the explainthatstuff.com QR code up above, we have:

A labelled diagram showing the key features of QR codes, including the finder, timing, and alignment patterns and data cells.

  1. Quiet zone: An empty white border that makes it possible to isolate the code from among other printed information (for example, on a dirty envelope, among the black and white print of a newspaper, or on smudged product packaging).
  2. Finder patterns: Large black and white squares in three of the corners make it easy to confirm that this is a QR code (and not, say, an Aztec code). Since there are only three of them, it's immediately obvious which way up the code is and which angle it's pointing at (unless the code is partly obscured or damaged in some way).
  3. Alignment pattern: This ensures the code can be deciphered even if it's distorted (viewed at an angle, printed on a curved surface, and so on).
  4. Timing pattern: This runs horizontally and vertically between the three finder patterns and consists of alternate black and white squares. The timing pattern makes it easy to identify the individual data cells within a QR code and is especially useful when the code is damaged or distorted.
  5. Version information: There are various different versions of the QR code standard; the version information (positioned near two of the finder patterns) simply identifies which one is being used in a particular code.
  6. Data cells: Each individual black or white square that's not part of one of the standard features (the timing, alignment, and other patterns) contains some of the actual data in the code.

Artwork: Above: Some of the key features in a QR code. Below: Features like this ensure a code can be read at high speed even when it's viewed at an angle, smudged, printed on a curved surface, or distorted in various other ways.

Further reading

There are a number of other features and complications that I won't go into here; if you'd like more detail, you'll find it by looking at these two excellent references:

What is 2D barcode technology used for?

A mobile boarding pass displayed on the screen of an iPhone.

Space Shuttle part with data matrix code engraved on it.

The American space agency NASA was one of the earliest organizations to make widespread use of data matrix codes, in the mid-1980s: it engraved them onto parts from space rockets, such as the Space Shuttle, because they didn't come off, like paper labels, and could store so much more information.

You can put a 2D barcode anywhere you can put a barcode (software for generating codes is easy to find online) and use it in very similar ways for tracking and tracing all kinds of objects. Cellphones with built-in 2D barcode readers are leading to other, more exciting applications. Advertisers who want you to find out more about their products online simply print a 2D barcode in the corner of their ads. Just point your cellphone at the code, scan it in, and your phone browser will automatically read the code, decode the Web address of the advertiser's site, and take you there instantly—no need to type in a tedious URL (website address) or anything like that. It's especially convenient for billboards, posters, and other ads you catch site of while you're on the move.

Transportation is another increasingly popular application. Numerous airline, railroad and bus companies let you buy travel tickets online in advance and store them on your cellphone. Your phone displays the details on its screen as a 2D barcode code, which becomes your electronic ticket (and, in the case of airlines, your boarding pass. German airline Lufthansa's Mobile Boarding Pass is an example.) Expect to see lots more 2D barcode applications appearing very soon!

Photo: Left: Using an iPhone as a mobile airline boarding pass. This is an app called MeeTicket that lets you store and display airline boarding passes from different airlines. Right: A data matrix code engraved onto a Space Shuttle part. Photo courtesy of NASA.

Find out more

On this website

Books

Patents

There's much more technical detail about how data-matrix codes and readers work in the following patents:

Photos

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Please do NOT copy our articles onto blogs and other websites

Text copyright © Chris Woodford 2009, 2012. All rights reserved. Full copyright notice and terms of use.

QR Code® is a registered trademark of Denso Wave Incorporated. Semacode is a trademark of Semacode Corporation.

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