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Two Dimensional (2D) Stacked Bar Code Symbologies

A 2D stacked symbology uses multiple rows of width modulated bars and spaces. Each row has the same physical length and appears as a conventional linear symbology. The adjacent row touch each other and may include separator bars for delineation. 

PDF417

PDF417 is a multi-row, variable length bar code symbol. It has the benefit of high capacity and error correction. It is capable of encoding more than 1,100 bytes, 1,800 ASCII characters, or 2,700 digits depending on the data compaction mode. PDF417 supports full ASCII character including extended character set. There are three configurations of PDF417, namely Standard PDF417, Macro PDF417 and Truncated PDF417.  

Standard PDF417 is the base of all PDF417 extended version. Macro PDF417 has the ability of distributing large files into a number of symbols. Truncated PDF417 reduces the symbol size but requires a clean environment for scanning.

The revision of PDF417 adds a new specification for Micro PDF417 into the set. 

Every symbol character uses 4 bars and 4 spaces in a 17 module length. There are 929 symbol characters in each of the 3 character sets. The number of rows and the row length is variable, allowing the symbol’s aspect ratio to be adjusted for particular labeling applications. 

PDF417 includes optional error correction characters. These become more important when shorter bar heights are used. The numberof error correction characters can be one of 8 possible values from 2 to 512. It is recommended that the number of error correction characters should be at least 10% of the number of data characters. 

Of the 929 characters, 900 are for encoding data, and the rest are to change the data compaction modes, namely, "Text", "Numeric, and "Byte". Text mode encodes 2 characters per symbol character, using 4 sub-modes of "Alpha", "Lower Case", "Mixed" and "Punctuation". The Numeric mode encodes almost 3 digits into 1 symbol character, and the Byte mode encodes up to six 8-bit bytes of digital data into 5 symbol characters.

Through the use of Global Label Identifiers (GLI), other data interpretations for special applications are possible. The 811,800 possible values of GLI makes it possible to be used for international character sets or user-defined interpretations in closed systems.

A concatenation scheme allowing up to 99,999 symbols to be linked to a large file is called "Macro PDF417". Another which allows smaller symbols to be printed if the symbol quality is expected to be high is called "Truncated PDF417".

2D Matrix Symbologies

A 2D matrix symbology encodes data into a 2D pattern of data cells. The data cells can consists of different colors and shapes, and may be separated by space containing no information.

DataMatrix

Each symbol has a unique perimeter pattern that is used for finding the symbol and its orientation. Two outside rows are solid,forming the L pattern, and the opposite 2 perimeter rows use an alternating black-white pattern which helps synchronize the decodingprocess.

MaxiCod

Originally called "DenseCode", then "UPSCode", sometimes also referred as "Hex Code". The symbology is used for automatic sortation and tracking of packages. It is a fixed length, alphanumeric symbology composed of an approximately square array of interlocking hexagons surrounding a circular pattern. MaxiCode specifies a fixed module size and symbol dimensions. A MaxiCode encodes 596-bit message with substantial redundancy.

QR Code

QR Code uses an array of square data cells and 3 fixed orientation targets, introduced by Nippondenso Company in 1994.

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