One-dimensional bar code only in one direction (usually the horizontal direction) to express information, and in the vertical direction does not express any information, its height is usually to facilitate the alignment of the reader.
One-dimensional bar code application can improve the speed of information entry, reduce the error rate, but one-dimensional bar code also has some shortcomings:
* Small data capacity: 30 characters or so
* Can only contain letters and numbers
* Bar code size is relatively large (space utilization is low)
* Bar codes can not be read after they have been damaged
A bar code that stores information in two-dimensional space, horizontally and vertically, is called a 2-dimensional bar code.
As with the one-dimensional bar code, two-dimensional bar code also has many different coding methods, or code system. As far as the coding principle of these codes is concerned, there are generally three types
1. Linear stacking two-dimensional code is based on the principle of one-dimensional bar code encoding, the number of one-dimensional code in the vertical stack generated. Typical code system such as: Code 16K, Code 49, PDF417 and so on.
2. The matrix two-dimensional code is encoded in a rectangular space by different distributions of black and white pixels in the matrix. Typical code system such as: Aztec, Maxi Code, QR Code, Data Matrix and so on.
3. The postal codes are encoded by different lengths of bars, mainly for mail encoding, such as: Postnet, BPO 4-State.
In many types of 2D bar codes, common code systems are: Data Matrix, Maxi Code, Aztec, QR Code, Vericode, PDF417, Ultracode, Code 49, Code 16K,
* Data Matrix is mainly used for identification of small parts of the electronics industry, such as Intel's Pentium processor on the back of the printed code.
* Maxi Code was developed by United Parcel Service (UPS) for sorting and tracking parcels.
* Aztec by the United States Welch (Welch Allyn) introduced, can accommodate up to 3832 numbers or 3067 alphabetic characters or 1914 bytes of data.
Below, we take PDF417 code as an example, describes the characteristics and characteristics of two-dimensional bar code.
Introduction to PDF417
PDF417 code by the Chinese in the United States Wang Yinjing (sound), Dr. invented. PDF is to take English Portable Data File three words acronym, meaning "portable data file". Since each symbol character constituting the bar code is composed of four bars and four empty spaces, if the narrowest bar or empty space constituting the bar code is referred to as a module, the above four bars and four empty total modules As 17, so called 417 yards or PDF417 yards.
The characteristics of PDF417
1. Large information capacity PDF417 code can be expressed in addition to letters, numbers, ASCII characters, but also the expression of binary numbers. In order to make the code more compact and improve the information density, PDF417 in encoding when there are three formats:
* Extended alphanumeric compression format can hold up to 1850 characters;
* Binary / ASCII format can accommodate 1108 bytes;
* Digital compression format can accommodate 2710 numbers.
2. Error correction capability One-dimensional bar code usually has a check function to prevent misreading, once the bar code is defaced will be rejected. The two-dimensional bar code can not only prevent errors, but also to correct the error, even if the bar code is partially damaged, but also can restore the correct information.
3. Printing requirements are not high Ordinary printing equipment can print, fax can also read.
4 can be used to read a variety of reading devices PDF417 code can be used with a grating laser reader, linear and surface scanning image reader to read.
5. Adjustable size to accommodate different print space
6 code system has become an international standard, China has also developed a national standard of 417 yards.
PDF417 correction function
Two-dimensional bar code error correction function is part of the information by repeated representation (redundant) to achieve. For example, in the PDF417 code, a line in addition to the information contained in the Bank, there are some other locations to reflect the characters (error correction code) information. In this way, even when a part of the bar code is damaged, it can also exist in other locations of the error correction code to restore its information out.
The correction capability of PDF417 is divided into 0 to 8 according to the number of words of error correction code. See Figure 4, the higher the level is, the more correct the code word is, the stronger the correction capability and the greater the bar code. When the correction level is 8, even if the bar code defacement 50% can also be read correctly, as shown in Figure 5.
PDF417 several variants
Figure 6, PDF417 there are several forms of deformation of the code system:
* PDF417 truncation code In a relatively "clean" environment, the possibility of bar code damage is small, the right of the line indicator can be omitted and reduce the terminator.
PDF417 microcode further reduced PDF.
* Macro PDF417 code When the contents of the file is too long, can not use a PDF417 code that can be used to contain multiple (1 ~ 99999) bar code macroblock PDF417 code to represent.
Advantages of 2D barcodes
From the above description can be seen, compared with the one-dimensional bar code has a clear advantage of two-dimensional bar code, summed up in the following areas:
1). Data capacity is greater
The PDF417 code in the figure contains all the text in the text box.
2). Exceeding the alphanumeric limit
3). Bar code relative size is small
4). Has the ability to resist damage
Application of 2D Bar Code
1). The application of the transport industry
A typical transport business process usually experienced: Supplier -> freight forwarders, freight forwarders -> freight companies, freight companies -> customers and several other processes, in each process are involved in the handling of shipping documents. The shipping document contains a lot of information, including: consignor information, consignee information, cargo list, mode of transport and so on. The premise of document processing is the input of data, the way of manual keyboard entry has the problems of low efficiency and high error rate, which can not meet the requirements of modern transportation industry.
Two-dimensional bar code in this regard provides a good solution to the contents of the document into a two-dimensional bar code, printed on the shipping documents, all aspects of the transport business using two-dimensional bar code reader to scan the bar code, the information will be Entered into the computer management system, both fast and accurate.
In the United States, although the EDI application innovation in the core of business processes, but unfortunately it ignores the key role in the process - the shipping company. Many EDI messages are always late for the freight forwarder, which can affect the transport of goods and the generation of customer documents due to the inability to confirm the accurate shipping information in time.
The American Freight Association (ATA) has therefore proposed a paper EDI system. The sender encodes the EDI information in a PDF417 barcode label and forwards it to the freight forwarder, which scans the barcode and immediately forwards the information to the carrier's computer system. All this happens at the right time and in the right place, making the overall transport process much more efficient.
2). The application of identification cards
The US Department of Defense has been printed on the military identity card PDF417 code. The cardholder's name, rank, photo and other personal information are encoded into a PDF417 code printed on the card. Card is used to do an important place in and out of management and hospital management.
The application of the advantages of real-time data acquisition, low implementation costs, card damage (such as shooting) can read, and security.
China's Hong Kong Special Administrative Region of the resident identity card also used PDF417 code. Other applications, such as business licenses, driver's licenses, passports, temporary residence permits for migrants in urban China, medical insurance cards are also very good application direction.
3). File and table applications
Every agent of Seimei Insurance in Japan carries a laptop when meeting with customers. Each policy and agreement is produced and printed on the computer. When they return to the office after the need to manually enter the policy data to the company's host.
In order to improve the accuracy and speed of data entry, they make policy at the same time the policy content compiled into a PDF417 bar code, printed on the document, so they can use two-dimensional bar code reader to scan the bar code data entry host.
Other similar applications are: customs declarations, tax declarations, various forms of government departments, and so on.
4) Asset tracking
American Pipe has various types of pipes in various locations that require maintenance. In order to track each tube, they will pipe the number, location number, manufacturer, length, grade, size, thickness and other information into a PDF417 bar code, made of labels attached to the tube. When the pipe is removed or installed, the operator scans the bar code label and the database information is updated in time.
Factories can use two-dimensional bar code to track production equipment; hospitals and clinics can also use two-dimensional bar code label tracking equipment, computers and surgical instruments.
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