QR Code Technology : How A QR Code Works
The data in a QR Code is 2D, meaning information is encoded both vertically and horizontally. The interface allows the user to create three different sizes as defined below:
A Basic QR Code - Most Are Black and White
1. Alphanumeric – 4, 296 characters
2. Numeric – 7,089 characters
3. 8 bit Binary – 2, 953 bytes
Depending on which of the four error correction schemes are used, the amount of space truly available could be smaller–the outline merely represents the maximum possible for each scenario. The error correction algorithm is based upon Reed-Solomon, and comes in four variations:
1. Level L – 7% of characters can be restored (default)
2. Level M – 15% of characters can be restored (most often used)
3. Level Q – 25% of characters can be restored
4. Level H – 30% of characters can be restored
Level L and M are most suitable for codes found in clean environments. Level Q and H are for dirty environments, like manufacturing plants. The error correction level that you use will dictate the amount of text that can be encoded.
Up to 30% Damage and Still Readable!
“30% seems really high to me so for it to work is amazing.”
A QR code is a square with an equal number of rows and columns.
1. They start at 21 rows and columns and increment by fours.
2. The next size up is 25 rows and columns
3. The next is 29 rows and columns.
4. This increment continues until the 40th step where it’s 177 rows and columns.
Each step is called a version. There are 40 versions available.
The following QR code is an example of version eight, and contains alphanumeric text.
This QR Code contains a lot of information as indicated by the dots.
A Basic QR Code Contains Five Major Sections
Main QR code sections outlined:
1. There are three position detection pattern codes located in three of the four corners. This allows 360 degree (omni-directional) high-speed reading of the code.
2. The timing pattern code help to detect the position of each cell in the QR code by the decoder application.
3. Solomon-Reed error correction and formatting / mask pattern information codes.
4. The data area is an array of rows and columns. Each cell is stored as a binary number (1 and 0). Error correction codes are inserted into this area as well.
5. Buffer zone (also called the quite zone) to isolate the code from other packaging information. This zone is four cells wide.
6. In more complex QR codes there is a sixth function called the alignment pattern which will be located in the lower right hand corner. This pattern allows the QR reader to correct for distortion when the code is bent or curved.
QR Code Data Area
QR Code Location Boxes and Alignment Box
The three prominent boxes in the corners of each code indicate the location of the image (so it can be centered by the image parser). Another smaller box in the lower-right aligns the image. The rest of the blocks indicate the information specific to the international standards and finally the identifying data contained within the code.
In the next image, you see that the QR Codes data area is organized into an array of cells organized into a 2D matrix where information is encoded both vertically and horizontally. The number of alignment
patterns used depends upon how much information is being encoded.
QR Code Linking Functionality
QR codes also have linking functionality, meaning that a single large code can be divided into two or more codes, up to a maximum of 16 codes. This allows for the delivery of larger data sets that can more easily be decoded.