By John R Joyce, Ph.D
http://www.scientificcomputing.comThe Quick Response Code was created by Denso-Wave Incorporated,1 a subsidiary of Toyota, in 1994 and is a two-dimensional bar code. I mention it because it has rapidly become one of the most commonly publicly used matrix codes, though you might be more familiar with it under the Denso-Wave trademark of QR Code. If you were in attendance at Pittcon 2012, despite a tweet from someone saying that they hadn’t seen a QR code anywhere, you will no doubt have noticed that they were everywhere! You could find them on everything; including business cards, programs, part of exhibit booths, and even printed on T-shirts.This growing popularity is a result of their flexibility, data capacity and the explosion in the number of smart phones available. While the use of QR codes in the United States has grown rapidly, we are well behind their use in Japan, where it is found everywhere, with places such as the Netherlands and South Korea only a little behind.
QR codes come in a variety of versions with different data capacities, but always appear in a square pattern containing a number of fixed data elements. These are illustrated in th embedded Wikipedia graphic in Figure 1.2Because of the encoding used, the capacity for a given version varies with the specific data to be stored in it. For example, Version 1 consists of a 21 by 21 matrix and can hold between 10 and 25 characters. Version 4 consists of a 33 by 33 matrix and can hold between 67 and 114 characters. By the time you reach Version 40, with a 177 by 177 matrix, the code can contain between 1852 to 4296 characters. If you are only encoding numbers, instead of alpha-numeric characters, the maximum number of digits that can be encoded rises to 7,089. This gives you the ability to encode a great deal of information, but the numbers above only tell part of the story.
|Figure 2: Customized QR Code from 360i|
Using Reed–Solomon error correction, damaged codes still can be read. How much damage can be absorbed depends on the level of error correction used. For example, Level L error correction allows seven percent of the code words to be restored, while Level H error correction allows 30 percent of the code words to be restored.
However, this code restoration capability does come at a price. For code restoration to work, redundant data must be included in the code, meaning that fewer data characters can be encoded. The bottom line is that how much you can actually store in this code, as with so many things in life, is a trade-off. The full description of version 2 of this code can be found in standard ISO/IEC 18004:2006.3 Leer más “Quick Response Code”