Aztec Code

The Aztec Code is a matrix code invented by Andrew Longacre, Jr. and Robert Hussey in 1995. The code was published by AIM, Inc. in 1997. Although the Aztec Code was patented, that patent was officially made public domain. The Aztec Code is also published as ISO/IEC 24778:2024¹ standard. Named after the resemblance of the central finder pattern to an Aztec pyramid, Aztec Code has the potential to use less space than other matrix barcodes because it does not require a surrounding blank "quiet zone".

The Aztec Code is a matrix code invented by Andrew Longacre, Jr. and Robert Hussey in 1995. The code was published by AIM, Inc. in 1997. Although the Aztec Code was patented, that patent was officially made public domain. The Aztec Code is also published as ISO/IEC 24778:2024 standard. Named after the resemblance of the central finder pattern to an Aztec pyramid, Aztec Code has the potential to use less space than other matrix barcodes because it does not require a surrounding blank "quiet zone". File:Aztec Code with desc.png|The core of the compact Aztec code (red ascending diagonal hatching), showing the central bull's-eye, the four orientation marks (blue diagonal cross-hatching), and space for 28 bits (7 bits per side) of coding information (green horizontal hatching). The first ring of data begins outside that (grey descending diagonal hatching). File:Aztec code full core.png|The core of the full Aztec code. 40 bits are available between the orientation marks for encoding parameters. File:Aztec Encoding.svg|Compact Aztec symbol encoding the message, 'Wikipedia, the free encyclopedia'. Message data is placed in a spiral pattern around the core. The mode message begins "01011100", indicating 01 2 +1 = 2 layers, and 011100 2 +1 = 29 data codewords (of 6 bits each). The message data is encoded using a (63,52) Reed-Solomon code (shortened to (40,29) and corresponding to 29 data words and 11 error correction words of 6 bits each) over GF(64). Error correction words are represented as E1 through E11. The mode message is protected by a (15,10) Reed-Solomon code (shortened to (7,2) and corresponding to 2 data words and 5 error correction words of 4 bits each) over GF(16). The compact Aztec code core may be surrounded by 1 to 4 layers, producing symbols from 15×15 (room for 13 digits or 12 letters) through 27×27. There is additionally a special 11×11 "rune" that encodes one byte of information. The full core supports up to 32 layers, 151×151 pixels, which can encode 3832 digits, 3067 letters, or 1914 bytes of data. Whatever part of the symbol is not used for the basic data is used for Reed–Solomon error correction, and the split is completely configurable, between limits of 1 data word, and 3 check words. The recommended number of check words is 23% of symbol capacity plus 3 codewords. Aztec Code is supposed to produce readable codes with various printer technologies. It is also well suited for displays of cell phones and other mobile devices. x/S = Shift to mode x for one character; B/S = shift to 8-bit binary x/L = Latch to mode x for following characters Punct codes 2–5 encode two bytes each The table lists ASCII characters, but it is the byte values that are encoded, even if a non-ASCII character set is in use B/S (binary shift) is followed by a 5-bit length. If non-zero, this indicates that 1–31 8-bit bytes follow. If zero, 11 additional length bits encode the number of following bytes less 31. (Note that for 32–62 bytes, two 5-bit byte shift sequences are more compact than one 11-bit.) At the end of the binary sequence, the previous mode is resumed. FLG(n) is followed by a 3-bit n value. n=0 encodes FNC1. n=1–6 is followed by 1–6 digits (in digit mode) which are zero-padded to make a 6-bit ECI identifier. n=7 is reserved and currently illegal.

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