Generating QR Codes in Linux
Creating and Reading QR CodesBy
With the right tools, you can create your own QR code squares with information you want to share on a business card, in a letter, or on your website.
Read errors of unreliable, one-dimensional bar codes often caused interruptions in industrial production, prompting companies like Toyota and its subsidiary Denso Wave to develop as early as 1994 a new code for acquiring stock data. The new matrix bar code was designed to store more information than the traditional bar code and to stay legible, even if the label was dirty, wrinkled, or partially destroyed.
The quick response code, or QR code, comprises a matrix of square dots instead of the usual lines. Measuring up to 177 by 177 dots, the QR code encodes up to 4,296 characters, compared with a bar code that encodes just 13.
Thanks to numerous free reader apps for smartphones, QR codes have gained in popularity in recent years. Posters, catalogs, magazines, business cards, and even television screens display the small squares, offering additional information or URLs for microsites.
On My Mark!
The quickest way to create a QR code is with the Qrencode command-line utility. Any major distribution can install Qrencode via the package manager. The following command then creates a QR code containing the text “Hello World!” (Figure 1):
$ qrencode -o qrcode.png 'Hello World!'
The generated QR code ends up in the qrcode.png file. If the file already exists, it’s overwritten without prompting. If you have at least version 3.3.0 (qrencode -V), Qrencode can generate an EPS graphic,
$ qrencode -t EPS -o qrcode.eps 'Hello World!'
or ASCII output (Figure 2).
In the QR code image, the software creates a white border the width of one dot. This facilitates the process of deciphering the code for programs or the smartphone later on. If desirable, you can increase or decrease the edge with the -m parameter; in the following example the border width would be 10 code pixels:
$ qrencode -m 10 -o qrcode.png 'Hello World!'
If you are saving the QR code in PNG format, the -s parameter specifies the height of a black QR code pixel. By default, Qrencode draws every black dot three by three pixels. The program creates a slightly smaller QR code with quite a wide margin with the following command:
$ qrencode -s 2 -m 10 -o qrcode.png 'Hello World!'
A white border appears around the QR code that is exactly 20 screen pixels wide (10 QR code dots in width, with each dot two pixels). If you are creating EPS images, the only parameter available is -m; -s moves the entire QR code out of the image in this case. To control the resolution of PNGs further, use the -d parameter to define the dpi.
Besides the specified data, the QR code contains additional error correction information. If a portion of the image is damaged, it allows you to reconstruct the missing or illegible data. The more additional information the QR code contains, the more heavily damaged it can be without becoming useless.
Increasing the error tolerance increases the size of the image because you need more black dots (Figure 3).
The QR code standard thus uses four levels of error correction: H level allows you to read all data if 30 percent of the QR code is destroyed, Q level if 25 percent is unreadable, and M level if just 15 percent is unintelligible. At the lowest level, L, only 7 percent of the data can be faulty. In Qrencode, the -l parameter selects the error correction level. The possible values are pretty much what you would expect: L, M, Q, and H.
The level you choose depends on the proposed use. If you expect the QR code to be exposed to external influences (e.g., wind, weather, graffiti) or if you are planning to manipulate the image deliberately (see the “Intruders” box), you will want the highest level, H. On a business card, the lowest level, L, is sufficient. If in doubt, simply omit the -l parameter. The program then uses level L by default.
Qrencode lets you encode any text, including URLs. You only need to use single quotes if blanks and non-standard characters app