PDF417 is a two-dimensional, variable-length stacked symbology that was developed in 1992 to encode large amounts of data in a small area. Its name derives from its format: a portable data file (PDF) that carries four bar elements and four space elements arranged in a 17-module codeword. The symbology is in the public domain.
PDF417 is used in a variety of settings: Government-issued identification cards (such as driver's licenses), airline boarding passes, postage stamps, and package labels, to name a few.
PDF417 has two specialized variants: Macro PDF417 and Compact PDF417. Macro PDF417 is used to divide files that are too large to be encoded in a single symbol into smaller, encodable segments. Compact PDF417 is used when space considerations are a main concern and symbol damage is unlikely. (Compact PDF417 is not to be confused with MicroPDF417, which is a different symbology.)
PDF417 is defined in ISO/IEC 15438 - Information technology - Automatic identification and data capture techniques - PDF417 bar code symbology specification.
The symbol comprises the following elements per row:
Leading quiet zone
Left row indicator codewords
Right row indicator codewords
Trailing quiet zone
Each PDF417 symbol contains between 3 and 90 rows. Both row height and error correction are variable and adjustable. A symbol that has error correction set to the minimum level supports up to 1,850 text characters, 2,710 digits, or 1,108 bytes.
This symbology supports all 256 ASCII characters and 8-bit binary data.
PDF417 uses data compaction schemes to enhance encoding efficiency. The following modes are used to map between user-defined data and codeword sequences:
Text Compaction mode
Byte Compaction mode
Numeric Compaction mode
It is possible to switch between modes in a symbol.
PDF417 uses the Reed-Solomon algorithm for error correction. Four selectable levels of error correction are available, which enables the barcode to be read even if up to 50 percent of the code is damaged.
PDF417 symbol dimensions depend on the amount of data that is entered. The height of any PDF417 symbol can range from 3 to 90 rows, and the row height can range from 1X to 10X, where "X" is the current X dimension. The width of a symbol can range from 90X to 583X. A minimum quiet zone of 2X is required on all sides.
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