Barcodes that store information in two-dimensional space in horizontal and vertical directions are called two-dimensional barcodes.
Classification of (1) 2D barcode
Like one-dimensional bar code, two-dimensional bar code has many different coding methods, or coding systems. As far as the coding principle of these codes is concerned, they can usually be divided into the following three types:
① Linear stacked QR codes are formed by vertically stacking multiple one-dimensional codes on the basis of one-dimensional bar code coding principle. Typical coding systems are: Code 16K, Code 49, PDF4 17, etc.
② Matrix QR codes are coded in rectangular space by different distributions of black and white pixels in the matrix. Typical coding systems include: Aztec, Maxi code, two-dimensional code, data matrix and so on.
(3) Postal codes are coded by bars with different lengths, which are mainly used for mail coding, such as Postnet, BPO 4-State, etc.
Among many kinds of 2D barcodes, the commonly used coding systems are: Datamatrix, Maxicode, AZTEC, QR code, Vericode, PDF 4 17, Ultra Code, Code 49, Code 16K, etc. , in which:
The data matrix is mainly used to identify small parts in the electronics industry, such as the code printed on the back of the Intel Pentium processor.
Maxi Code was developed by United Parcel Service Company (UPS) to sort and track parcels.
Aztec, introduced by Welch Allyn Company of the United States, can accommodate up to 3832 numbers or 3067 alphabetic characters or 19 14 bytes of data.
Next, we take PDF4 17 code as an example to introduce the characteristics and characteristics of two-dimensional code.
(2) Introduction of PDF 417
The code PDF4 17 was invented by Dr. Wang, a China student studying in the United States. PDF is the abbreviation of English portable data file, which means "portable data file". Because each symbol character that constitutes a bar code consists of four bars and four spaces, if the narrowest bar or space that constitutes a bar code is called a module, then the total number of modules of the above four bars and four spaces must be 17, so it is called 4 17 code or PDF4 17 code.
(3) the characteristics of pdf 417
① Large information capacity: PDF4 17 code can represent not only letters, numbers and ASCII characters, but also binary numbers. In order to make the encoding more compact and improve the information density, PDF4 17 has three formats when encoding:
The expanded alphanumeric compression format can accommodate 1850 characters;
Binary /ASCII format can hold 1 108 bytes;
The digital compression format can accommodate 27 10 numbers.
② Error correction ability: One-dimensional bar codes usually have verification function to prevent misreading. Once the bar codes are defaced, they will be rejected. Two-dimensional bar code can not only prevent errors, but also correct them. Even if the bar code is partially damaged, the correct information can be recovered.
③ Ordinary printing equipment with low printing requirements can print and fax can read.
④ PDF4 17 code can be read by various reading devices, laser readers with grating and image readers with line scanning and area scanning.
⑤ The size can be adjusted to suit different printing spaces.
⑥ Code system has become an international standard, and China has also formulated a national standard of 4 17 code.
(4) The error correction function of PDF 417.
The error correction function of two-dimensional bar code is realized by repeating (redundant) some information. For example, in the PDF4 17 code, a line contains not only the information of its own line, but also some information reflecting the characters in other positions (error correction code). In this way, even when a certain part of the bar code is damaged, its information can be recovered by error correction codes existing in other places.
The error correction capability of PDF4 17 is divided into 0~8***9 levels according to the number of error correction codes. The higher the level, the more correction codes, the stronger the correction ability and the larger the bar code. When the correction level is 8, even if the barcode is defaced by 50%, it can be read correctly.
(5) Several variants of PDF 417.
PDF4 17 also has several different coding forms:
In the relatively clean environment of PDF4 17 truncation code, the possibility of bar code damage is very small, so the line indicator on the right can be omitted to reduce the terminator.
PDF4 17 microcode further reduces the PDF code.
Macro PDF4 17 code When the file content is too long to be represented by a PDF4 17 code, it can be represented by a macro PDF4 17 code and multiple barcodes (1~99999).
Advantages of 3.2D barcode
As can be seen from the above introduction, compared with one-dimensional bar code, two-dimensional bar code has obvious advantages, which can be summarized as follows:
Greater data capacity
The limit of alphanumeric characters is exceeded.
The size of the bar code is relatively small.
Have the ability to resist injury
Application of 4.2D barcode
Application of (1) in transportation industry
A typical transportation business process usually goes through: suppliers-> suppliers; Freight forwarder, freight forwarder-> Freight company, freight company-> Several processes, such as customers, involve the processing of delivery documents in each process. Freight documents contain a lot of information, including: shipper information, consignee information, cargo list, mode of transportation and so on. The premise of document processing is data entry. Manual keyboard input method has the problems of low efficiency and high error rate, which can no longer meet the requirements of modern transportation industry.
Two-dimensional bar code provides a good solution in this respect. It is fast and accurate to compile the contents of the documents into two-dimensional codes, print them on the delivery note, scan them with two-dimensional code readers in all aspects of the transportation business, and input the information into the computer management system.
In the United States, although EDI application has revolutionized the core part of business process, it unfortunately ignores the key role in the process-freight company. Many EDI messages are always late for freight forwarders, which leads to the failure to confirm the accurate freight document information in time, and affects the freight transportation and the generation of customer documents.
The American Freight Association (ATA) therefore proposed a paper EDI system. The sender compiles the EDI information into a PDF4 17 barcode label and submits it to the freight forwarder. By scanning the bar code, the information is immediately transmitted to the freight forwarder's computer system. All this happened at the right time and place, which greatly improved the efficiency of the whole transportation process.
(2) Application of ID card
The U.S. Department of Defense printed the code PDF4 17 on military ID cards. The cardholder's name, rank, photo and other personal information are compiled into PDF4 17 code and printed on the card. This card is used to manage access to important places and hospital visits.
The advantages of this application are real-time data acquisition, low implementation cost, reading even if the card is damaged (such as shooting), and anti-counterfeiting.
The identity card of the Hong Kong Special Administrative Region also adopts the encoding of PDF4 17. Other applications, such as business license, driver's license, passport, temporary residence permit for urban floating population in China, medical insurance card, etc. It is also a good application direction.
(3) Application of documents and forms
Every broker of Seimei Insurance Company in Japan will take a laptop with him when meeting customers. Every policy and agreement is made and printed in the computer. When they return to the office, they need to manually input the policy data into the company's mainframe.
In order to improve the accuracy and speed of data entry, they compiled the contents of the policy into PDF4 17 barcode when making the policy, and printed it on the document, so that they could scan the barcode with a two-dimensional barcode reader and enter the data into the host.
Other similar applications include: customs declaration forms, tax returns, various application forms of government departments and so on.
(4) Asset tracking
American steel pipe company has different kinds of pipes to be maintained in different places. In order to track each pipe, they compiled the information such as the number, location number, manufacturer, length, grade, size and thickness of the pipe into a PDF4 17 barcode, and made a label and stuck it on the pipe. When the pipeline is dismantled or installed, the operator scans the bar code label and the database information is updated in time.
Factories can track production equipment with two-dimensional bar codes; Hospitals and clinics can also use two-dimensional bar code tag tracking equipment, computers and surgical instruments.
5. Mixed code and its application
With the development of society, the progress of science and technology, the improvement of people's living standards and the intensification of market competition, people's requirements for information are constantly improving. One-dimensional bar code is used in some traditional fields, such as commerce, medicine, logistics and transportation. Due to the limitation of information capacity (generally only the identification number of goods or businesses can be identified), it is increasingly unable to meet people's requirements. The continuous progress of two-dimensional bar code technology is causing changes in these application fields.
The UCC organization (Unified Coding Committee) of the United States has introduced a new coding system-hybrid code, which is a combination code of one-dimensional code and two-dimensional code, in which:
One-dimensional code composition can be:
UCC/EAN- 128
UPC /EAN
Reduced space symbology (RSS)
Component of QR code can be:
CC-A (a variant of PDF4 17 microcode dedicated to mixed code)
CC-B (standard PDF4 17 microcode)
CC-C (standard PDF4 17)
The one-dimensional barcode part contains the identification number, while the two-dimensional barcode part contains supplementary information.
It can be read by linear CCD and laser scanner with grating in the future.
Application of (1) mixed coding in logistics and transportation business
UCC/EAN- 128, supplemented by two-dimensional bar code, provides information such as order number, invoice, route information, electronic backup of delivery notice, packaging, content and batch number.
(2) Application of mixed coding in drug circulation.
Using two-dimensional code to record supplementary information can provide effective period to facilitate drug turnover, and record batch number to facilitate drug tracking.
(3) The application of hybrid coding in retail industry.
Marking the batch number and shelf life on food, especially fresh and frozen perishable things, can greatly improve the turnover efficiency of goods. Electronic products can also be marked with revision information of software and hardware.
6.2D barcode reader
Two-dimensional bar code reading equipment can be divided into:
Linear CCD and linear imager can read one-dimensional bar codes and linearly superimposed two-dimensional codes (such as PDF4 17). When reading a QR code, we need to scan the whole barcode vertically, which is called "scanning reading". This kind of products are cheaper and cost-effective;
The laser reader with grating can read one-dimensional bar code and linearly superimposed two-dimensional code. When reading the QR code, aim the light at the bar code, and the grating element completes vertical scanning without manual scanning.
Image reader is a high-end device, which can read one-dimensional bar codes and various two-dimensional bar codes by taking pictures and analyzing and decoding.
Welch Alin Company is one of the world's leading manufacturers of barcode reading equipment, and its CCD technology, image reader technology and decoding technology are in the leading position in the world. Recently, she put forward a new concept of linear imaging technology. Based on advanced technology, Weiling's two-dimensional bar code reading equipment has been leading the world trend, and its main products include IT3800 and IT4400 series.
data matrix
Development of two-dimensional bar code of data matrix
The original name of 2D barcode of data matrix is Datacode, which was invented by ID Matrix in 1989. Data-Matrix two-dimensional barcode is a kind of matrix two-dimensional barcode, and its development idea is to store more data on smaller barcode labels. The minimum size of two-dimensional bar code of data matrix is the smallest among all bar codes at present, which is especially suitable for marking small parts and printing directly on entities.
Two-dimensional barcode of data matrix can be divided into ECC000- 140 and ECC200. ECC000- 140 has many different levels of error correction functions, while ECC200 calculates error correction codes by polynomial generated by Reed-Solomon algorithm, and its size can be printed in different sizes as required. But the error correction code used should match the size. ECC200 is widely used because of its simple algorithm and flexible size. This section only introduces the data matrix QR code of ECC200 specification, and the following data matrix QR code actually refers to ECC200.
The appearance of two-dimensional bar code of graph data matrix
As shown in the figure, the appearance of the two-dimensional bar code of the data matrix is a square or rectangular symbol composed of many small squares, and its information is stored as a binary code through the arrangement and combination of bright and dark squares, so the computer can directly read its data content without the need for a character lookup table like the traditional one-dimensional bar code. Dark color stands for "1" and light color stands for "0", and then a series of light and dark squares are used to describe special character information, and these strings are listed into a complete matrix code to form a DataMatrix two-dimensional barcode, which is printed on different material surfaces by different printers. Because the two-dimensional bar code of data matrix can be accurately read only by reading 20% of the data, it is very suitable for printing in places where the bar code is easily damaged, such as parts exposed to high heat, chemical cleaners, mechanical erosion and other special environments.
The size of the two-dimensional bar code of the data matrix can be adjusted at will, with a maximum of 14 square inch and a minimum of 0.0002 square inch. This size is also the smallest in one-dimensional and two-dimensional bar codes at present, so it is especially suitable for printing on components of circuit boards. On the other hand, the size of most barcodes is absolutely related to the amount of encoded data, but the size of two-dimensional barcodes of data matrix has nothing to do with the amount of encoded data, so its size is more flexible. In addition, the maximum storage capacity of DataMatrix two-dimensional bar code is 2000 bytes, and its automatic error correction ability is low, which is only suitable for special CCD scanner to interpret.
Structure of two-dimensional bar code of data matrix
(A) Characteristics
Data matrix two-dimensional bar code has the following characteristics:
Codeable character set includes all ASCII characters and extended ASCII characters, ***256 characters.
Bar code size (excluding blank area):10×10 ~144×144.
Data capacity: 235 alphanumeric data, 1556 8-bit data, 3 1 16 digital data.
Error correction: Error correction code is calculated by polynomial generated by Reed-Solomon algorithm. Different sizes should use different numbers of error correcting codes.
(2) Basic structure
The two-dimensional bar code symbol of each data matrix consists of a data area composed of square modules arranged regularly, and the data area is surrounded by viewfinder patterns and blank areas separated by alignment patterns.
Positioning figure
The positioning figure is the perimeter of the data area, that is, the width of the module. Adjacent two sides are dark solid lines, which are mainly used to define physical dimensions; Positioning and symbol distortion. The other two adjacent edges are alternately composed of light and dark modules, which are mainly used to define the unit structure of symbols, but can also help to determine the physical size and distortion.
Symbol size
ECC000- 140 symbol has odd rows and odd columns. The appearance of the symbol is a square matrix with dimensions ranging from 9×9 to 49×49, excluding blank areas. These symbols can be identified by the black square in the upper right corner.
The symbol of ECC200 has even rows and even columns. Some symbols are squares with sizes ranging from 10× 10 to 144× 144, excluding blank areas. Some are rectangular, ranging in size from 8× 18 to 16×48, excluding blank areas. All ECC200 symbols can be identified by the bright square in the upper right corner.
Data representation method
The two-dimensional barcode of data matrix represents data according to the following steps:
data coding
Firstly, the data to be represented is analyzed, and an appropriate coding scheme is selected. According to the selected scheme, the data stream is converted into a code stream, and necessary words are added. If the user does not specify the matrix size, the minimum size that can satisfy the data to be stored should be selected. DataMatrix 2D barcode * * * has six coding schemes, namely six code sets, as shown in table 10. 1.
Coding scheme and corresponding character set of two-dimensional bar code of data matrix
Coding scheme character set
ASCII decimal number
ASCII value 0~ 127
Extended ASCII value 128~255
C40
Basic uppercase number type
Basic lowercase alphanumeric type of text
EDIFACT 32~94
Base256 0~255
X 12 ANSI X 12 EDI data set
Error detection and correction code (ECC) generation
For the 2D barcode of data matrix with less than 255 characters, the error correction code can be calculated from the data code. For symbols with more than 255 codes, the data code should be divided into multiple modules, and then the error correction code of each module should be generated. Error-correcting codes can correct two kinds of error codes, including E-error (error code of known position) and T-error (error code of unknown position). In other words, an E-error is a symbol that cannot be scanned or decoded, and a T-error is a symbol that is decoded incorrectly.