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2D Barcode Electronic Ticket System Wing Gate Swing Gate Introduction
Double-tap auto scroll Submitter: admin Release time: 2008-09-28

What is a two-dimensional barcode
According to different personal habits, the two-dimensional code is also called two-dimensional bar code or two-dimensional bar code. Two-dimensional bar code / two-dimensional bar code (2-dimensional bar code)
A specific geometric figure records the symbol information of the data in black and white in a plane (in the two-dimensional direction) according to a certain rule; it is clever in the coding
Using the concept of "0" and "1" bitstreams that form the internal logic foundation of a computer, a number of geometric shapes corresponding to binary are used to represent text numeric information
Information, automatically read by image input equipment or photoelectric scanning equipment to realize automatic processing of information: it has some common features of bar code technology: each code system has its own characteristics
A certain character set; each character occupies a certain width; has a certain check function. It also has an automatic identification function for different rows of information, and a processing diagram
Shape rotation changes.
Two-dimensional bar code / two-dimensional code can express information in both horizontal and vertical directions, so it can express a large amount of information in a small area.

Classification of two-dimensional bar codes / two-dimensional codes
Two-dimensional bar codes / two-dimensional codes can be divided into stacked two-dimensional bar codes and matrix two-dimensional bar codes. Stacked / lined 2D barcodes are morphologically composed of multiple lines.
One-dimensional bar codes are stacked; matrix two-dimensional bar codes are formed in the form of matrices, and the dots on the corresponding element positions of the matrix are used to represent binary "1" and
"Empty" means binary "0", which is composed of a sequence of "dot" and "empty".

Stacking / rowing two-dimensional bar code
Stacked / row-type two-dimensional bar code (also known as stacked two-dimensional bar code or layered two-dimensional bar code). Its coding principle is based on one-dimensional bar code.
Stacked in two or more rows. It inherits some features of one-dimensional barcodes in coding design, verification principles, and reading methods. Reading equipment and barcode printing and
-Dimensional barcode technology compatible. However, due to the increase in the number of lines, it is necessary to determine the lines, and its decoding algorithm and software are not exactly the same as one-dimensional bar codes. Representative
Row and row 2D barcodes are: Code 16K, Code 49, PDF417, etc.

2. Matrix QR code
Short matrix two-dimensional bar code (also known as checkerboard two-dimensional bar code). It encodes in a rectangular space by different distributions of black and white pixels in a matrix. In the moment
At the position of the corresponding element of the matrix, the occurrence of dots (square dots, dots, or other shapes) represents the binary "1", and the absence of dots represents the binary "0".
The column combination determines the meaning represented by the matrix 2D barcode. Matrix 2D barcode is based on computer image processing technology, combined coding principles, etc.
A new type of graphic symbol automatic reading and processing code system. Representative matrix 2D barcodes are: Code One, Maxi Code, QR Code, Data
Matrix, etc.
Among dozens of two-dimensional bar codes, the commonly used codes are: PDF417 two-dimensional bar code, Datamatrix two-dimensional bar code, Maxicode two-dimensional bar code, QR Code,
Code 49, Code 16K, Code one, etc. In addition to these common 2D barcodes, there are Vericode barcodes, CP barcodes, Codablock F
Barcodes, field codes, Ultratec barcodes, Aztec barcodes.

The difference between PDF417 (two-dimensional code) and one-dimensional code:
A multi-line barcode does not need to be connected to a database, and can store a large amount of data. It is used in: hospitals, driving licenses, material management, cargo transportation
When the barcode is damaged, the error correction can make the barcode decode PDF417 correctly. it
It is a multi-line, continuous, variable-length, symbolic symbol containing a large amount of data. Each barcode has 3-90 lines, each line has a start section, a data section,
Termination section. Its character set includes all 128 characters, and the maximum data content is 1850 characters.
One-dimensional barcodes only express information in one direction (usually horizontal direction), but do not express any information in the vertical direction. Its certain height is usually
It is to facilitate the alignment of the reader.
The application of one-dimensional barcode can increase the speed of information entry and reduce the error rate, but there are also some shortcomings in one-dimensional barcode.

* Small data capacity: about 30 characters
* Can only contain letters and numbers
* Relatively large barcode size (low space utilization)
* Cannot be read after the barcode is damaged

A barcode that stores information in a two-dimensional space in the horizontal and vertical directions is called a two-dimensional bar code.
Like one-dimensional barcodes, two-dimensional barcodes have many different encoding methods, or codes. As far as the coding principles of these codes are concerned, they can usually be divided into
The following three types:

Linear stacked QR code
It is based on the principle of one-dimensional barcode coding, and multiple one-dimensional codes are stacked vertically. Typical code systems such as: Code 16K, Code 49,
PDF417 and so on.

2. Matrix QR code
It encodes in a rectangular space by different distributions of black and white pixels in the matrix. Typical code systems such as: Aztec, Maxi Code, QR Code,
Data Matrix, etc.

Postal code
Encoded by bars of different lengths, mainly used for mail encoding, such as: Postnet, BPO 4-State.
In many kinds of 2D barcodes, the commonly used codes are: Data Matrix, Maxi Code, Aztec, QR Code, Vericode, PDF417,
Ultracode, Code 49, Code 16K, etc., among them:

* Data Matrix is mainly used for the identification of small parts in the electronics industry. For example, the code is printed on the back of Intel's Pentium processor.
* Maxi Code was developed by United Parcel Service (UPS) for sorting and tracking of packages.
* Aztec was launched by the American Welch Allyn company, and can hold up to 3832 numbers or 3067 alphabetic characters or 1914 bytes of data.

Below, we take the PDF417 code as an example to introduce the characteristics and features of the two-dimensional barcode.

A) Introduction to PDF417
The PDF417 code was invented by Dr. Wang Yinjing, a Chinese American. PDF is an acronym for the three words of English Portable Data File, meaning
"Portable Data File". Because each symbol character that composes a bar code consists of 4 bars and 4 spaces, if the narrowest bar or space that composes a bar code is called
One module, the total number of the above four bars and four empty modules must be 17, so it is called 417 or PDF417.

B) Features of PDF417

Large information capacity
PDF417 code can represent not only letters, numbers, and ASCII characters, but also binary numbers. In order to make the coding more compact and increase the information density,
PDF417 has three formats when encoding:

* Extended alphanumeric compression format can accommodate 1850 characters;
* Binary / ASCII format can hold 1108 bytes;
* Digital compression format can hold 2710 numbers.

Error correction ability
One-dimensional barcodes usually have a check function to prevent misreading, and will be rejected if the barcode is contaminated. And two-dimensional barcodes can not only prevent errors, but also correct
True and false Even if the barcode part is damaged, the correct information can be restored.

3. Printing requirements are not high
It can print on common printing equipment, and read faxes.

4. Can be read with multiple reading devices
PDF417 code can be read with a laser reader with grating, linear and area scanning image reader.

5. Adjustable size to fit different print space

6. The code system has become an international standard, and China has also established a national standard of 417 codes.

二维条形码的纠错功能是通过将部分信息重复表示(冗余)来实现的。 3) PDF417 error correction function The error correction function of the two-dimensional barcode is realized by repeated representation (redundancy) of some information. For example, in PDF417 code, a line contains the letter
In addition, there is some information reflecting characters (error correction codes) in other positions. This way, even when a part of the barcode is damaged,
Error correction codes elsewhere restore their information.

PDF417's error correction ability is divided into 9 levels from 0 to 8 according to the number of error correction codewords. See Figure 4. The higher the level, the more the number of correction codewords, the stronger the correction ability, and the
The shape code is also larger. When the correction level is 8, even 50% of the barcode can be read correctly.

Four) several variants of PDF417
PDF417 also has several variant coding systems:
* PDF417 truncated code
In a relatively "clean" environment where the probability of barcode damage is low, you can omit the line indicator on the right and reduce the terminator.
* PDF417 microcode
Further reduced PDF code.
* Macro PDF417 code
When the file content is too long to be represented by one PDF417 code, it can be represented by a macro PDF417 code containing multiple (1 ~ 99999) bar code blocks.

The advantages of two-dimensional barcodes can be seen from the introduction above. Compared with one-dimensional barcodes, two-dimensional barcodes have obvious advantages.

A) larger data capacity
B) Go beyond the alphanumeric limit
C) Relatively small barcode size
4) With anti-damage ability

Features of 2D barcodes / 2D codes

1. High-density coding, large information capacity: can accommodate up to 1850 capital letters or 2710 numbers or 1108 bytes, or more than 500 Chinese characters, more than ordinary bar codes
The information capacity is about tens of times higher.
2. Wide coding range: The barcode can encode pictures, sounds, text, signatures, fingerprints, and other information that can be digitized and expressed in barcodes; can
Represents multiple languages; can represent image data.
3. Strong fault tolerance and error correction: This allows the two-dimensional barcode to be read correctly and damaged when it is partially damaged due to perforation, dirt, etc
Up to 50% can still recover information.
4. High decoding reliability: It is much lower than the ordinary bar code decoding error rate of two parts per million, and the bit error rate does not exceed one ten million.
5. Encryption measures can be introduced: good confidentiality and security.
6. Low cost, easy to make and durable.
7. The shape and size of the bar code symbol are variable.
8. 2D barcodes can be read using a laser or CCD reader.

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