Encoding the code
Also known as Portable Data File 417, the 2D barcode, is in fact a multi-row, variable-length ‘stacked’ symbology developed in 1992 by Symbol Technologies.
The symbol is composed of 3–90 stacked rows. A PDF417 symbol character, or codeword, is the individual building block for the barcode and consists of 17 modules arranged into four bars and four spaces, thereby giving it the name of 417. The integral sections of the barcode include clearly defined Start and Stop patterns, the data columns, and the quiet zone (see diagram below).
PDF417 offers encoding a maximum data character capacity of 1850 text ASCII characters, 2710 numerals, or 1108 bytes. This amount of data encoded is a result of the manner in which the algorithm encodes the type of data, for example, numerals require a smaller codeword size to encode than an alphabet letter.
PDF417 uses Reed Solomon error correction. Error correction levels are user selectable and can be set from 0 for no error correction to 8, which is the highest level. This level indicates the amount of redundancy that is added to the encoded barcode. The benefit is the increased scan-ability; however, the downside is that the effective content size is reduced because the error correction takes up content space.
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