The one-dimensional barcode only expresses information in one direction (generally the horizontal direction), but does not express any information in the vertical direction. Its certain height is usually for easy alignment of the reader.
The application of one-dimensional bar code can increase the speed of information entry and reduce the error rate, but one-dimensional bar code also has some shortcomings:
* Small data capacity: about 30 characters * Can only contain letters and numbers * Barcode size is relatively large (space utilization is low)
* The barcode cannot be read after being damaged
Bar codes that store information in two-dimensional spaces in the horizontal and vertical directions are called 2-dimensional bar codes.
Like one-dimensional bar codes, two-dimensional bar codes have many different encoding methods, or code systems. As far as the coding principles of these coding systems are concerned, they can generally be divided into the following three types:
1. Linear stacked two-dimensional codes are generated by stacking multiple one-dimensional codes in the longitudinal direction based on the principle of one-dimensional bar code. Typical code systems are: Code 16K, Code 49, PDF417, etc.
2. The matrix two-dimensional code is encoded in a rectangular space through the different distribution of black and white pixels in the matrix. Typical code systems are: Aztec, Maxi Code, QR Code, Data Matrix, etc.
3. Postal codes are encoded by bars of different lengths, mainly used for mail encoding, such as: Postnet, BPO 4-State.
In many types of two-dimensional bar codes, commonly used code systems are: Data Matrix, Maxi Code, Aztec, QR Code, Vericode, PDF417, Ultracode, Code 49, Code 16K, etc., among which:
* Data Matrix is ​​mainly used for the identification of small parts in the electronics industry. For example, this code is printed on the back of Intel's Pentium processor.
* Maxi Code was developed by the United Parcel Service (UPS) company for sorting and tracking of parcels.
* Aztec is launched by the Welch Allyn company in the United States and can accommodate up to 3832 numbers or 3067 alphabetic characters or 1914 bytes of data.
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