ISO/IEC 24778:2024
(Main)Information technology — Automatic identification and data capture techniques — Aztec Code bar code symbology specification
Information technology — Automatic identification and data capture techniques — Aztec Code bar code symbology specification
This document defines the requirements for the symbology known as Aztec Code. It specifies the Aztec Code symbology characteristics, including: — data character encodation; — rules for error control encoding; — the graphical symbol structure; — symbol dimensions and print quality requirements; — a reference decoding algorithm; — user-selectable application parameters.
Technologies de l'information — Techniques automatiques d'identification et de capture des données — Spécification pour la symbologie de code à barres du code Aztec
General Information
Relations
Standards Content (Sample)
International
Standard
ISO/IEC 24778
Second edition
Information technology —
2024-04
Automatic identification and data
capture techniques — Aztec Code
bar code symbology specification
Technologies de l'information — Techniques automatiques
d'identification et de capture des données — Spécification pour la
symbologie de code à barres du code Aztec
Reference number
© ISO/IEC 2024
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ii
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and functions . 1
3.1 Terms and definitions .1
3.2 Symbols and functions .2
3.2.1 Mathematical symbols .2
3.2.2 Mathematical functions and operations .2
4 Symbology characteristics . 3
4.1 Basic characteristics .3
4.2 Summary of additional features .3
5 Symbol description. 4
5.1 Basic Aztec Code properties .4
5.2 Symbol structure .4
5.2.1 Aztec code layout .4
5.2.2 Core Symbol .6
5.2.3 Data fields .7
5.3 Symbol character structure and sequence .7
5.4 Symbol size and capacity .9
6 General encodation procedures . 10
7 Symbol structure .11
7.1 Fixed pattern structures .11
7.1.1 Fixed pattern types .11
7.1.2 Finder .11
7.1.3 Orientation bits . .11
7.1.4 Reference grid .11
7.2 Mode message encoding and structure .11
7.2.1 Mode message .11
7.2.2 Symbol size designator .11
7.2.3 Message length designator . 12
7.2.4 Error encodation for the mode message . 12
7.2.5 Module placement for the mode message . 12
7.3 Data message encoding and structure . 12
7.3.1 Data message . 12
7.3.2 Source message encoding . 13
7.3.3 Error encodation for the data message . 15
7.3.4 Module placement for the data message . 15
8 Structured Append . 16
9 Reader initialization symbols . .16
10 Extended Channel Interpretation (ECI) .16
10.1 ECI basic information and references .16
10.2 Encoding ECIs in Aztec Code .17
10.3 Code sets and ECIs .17
10.4 ECIs and Structured Append .17
10.5 Post-decode protocol.17
11 User considerations . 17
11.1 Choice of data and error correction level .17
11.2 User selection of encoded message .17
11.3 User selection of minimum error correction level .18
© ISO/IEC 2024 – All rights reserved
iii
11.4 User selection of Structured Append .18
11.5 User selection of optional symbol formats .18
12 Dimensions .18
13 User guidelines .18
13.1 Human readable interpretation .18
13.2 Autodiscrimination capability .19
13.3 User-defined application parameters .19
14 Reference decode algorithm . 19
14.1 General .19
14.2 Finding candidate symbols. 20
14.3 Processing the bullseye image . 20
14.4 Decoding the Core Symbol . 20
14.4.1 Bullseye mapping of module centres . 20
14.4.2 Mapping and sampling module centres . 20
14.4.3 Determining video sign and symbol format .21
14.4.4 Determining symbol orientation and mirror image reversal .21
14.4.5 Decoding the mode message .21
14.5 Decoding the data message .21
14.5.1 General .21
14.5.2 Mapping the data layers .21
14.5.3 Assembling the codewords .21
14.5.4 Checking the codewords . 22
14.6 Translating the datawords . . 22
14.6.1 Bit stream conversion and interpretation . 22
14.6.2 Creating the data bit stream . 22
14.6.3 Interpreting the bit stream . 22
15 Symbol quality .22
15.1 Quality assessment method . 22
15.2 Symbol quality parameters . 22
15.2.1 Fixed pattern damage (FPD) . . . 22
15.2.2 Axial non-uniformity (AN) . 23
15.2.3 Unused error correction . 23
15.2.4 “Print” growth . 23
15.2.5 Grid non-uniformity . 23
15.3 Symbol print quality grading . 23
15.3.1 Symbol grade . 23
15.4 Additional print process control measurements . 23
16 Transmitted data .23
16.1 Basic interpretation . 23
16.2 Protocol for FNC1 .24
16.3 Protocol for ECIs .24
16.4 Symbology identifier .24
16.5 Transmitted data example .24
Annex A (normative) Aztec Runes . .26
Annex B (normative) Error detection and correction .28
Annex C (normative) Topological bullseye search algorithm .31
Annex D (normative) Linear crystal growing algorithm .35
Annex E (normative) Fixed pattern damage (FPD) grading .36
Annex F (normative) Symbology identifiers .38
Annex G (informative) Aztec Code symbol encoding example .39
Annex H (informative) Achieving minimum symbol size .43
Annex I (informative) Useful process control techniques .46
© ISO/IEC 2024 – All rights reserved
iv
Bibliography .48
© ISO/IEC 2024 – All rights reserved
v
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
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ISO and IEC technical committees collaborate in fields of mutual interest. Other international organizations,
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
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IEC Directives, Part 2 (see www.iso.org/directives or www.iec.ch/members_experts/refdocs).
ISO and IEC draw attention to the possibility that the implementation of this document may involve the
use of (a) patent(s). ISO and IEC take no position concerning the evidence, validity or applicability of any
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In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 31, Automatic identification and data capture techniques.
This second edition cancels and replaces the first edition (ISO/IEC 24778:2008), which has been technically
revised.
The main changes are as follows:
— introduction of continuous grading for fixed pattern damages (FPDs);
— grading of print growth deleted and added reference to ISO/IEC 15415.
Any feedback or questions on this document should be directed to the user’s national standards
body. A complete listing of these bodies can be found at www.iso.org/members.html and
www.iec.ch/national-committees.
© ISO/IEC 2024 – All rights reserved
vi
Introduction
Aztec Code is a two-dimensional matrix symbology whose symbols are nominally square, made up of square
modules on a square grid, with a square bullseye pattern at their centre. Aztec Code symbols can encode
from small to large amounts of data with user-selected percentages of error correction.
Manufacturers of bar code equipment and users of the technology require publicly available standard
symbology specifications to which they can refer when developing equipment and application standards.
The publication of standardised symbology specifications is designed to achieve this.
© ISO/IEC 2024 – All rights reserved
vii
International Standard ISO/IEC 24778:2024(en)
Information technology — Automatic identification and
data capture techniques — Aztec Code bar code symbology
specification
1 Scope
This document defines the requirements for the symbology known as Aztec Code. It specifies the Aztec Code
symbology characteristics, including:
— data character encodation;
— rules for error control encoding;
— the graphical symbol structure;
— symbol dimensions and print quality requirements;
— a reference decoding algorithm;
— user-selectable application parameters.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 646, Information technology — ISO 7-bit coded character set for information interchange
ISO/IEC 8859-1, Information technology — 8-bit single-byte coded graphic character sets — Part 1: Latin
alphabet No. 1
ISO/IEC 15415, Information technology — Automatic identification and data capture techniques — Bar code
print quality test specification — Two-dimensional symbols
ISO/IEC 15424, Information technology — Automatic identification and data capture techniques — Data
Carrier Identifiers (including Symbology Identifiers)
ISO/IEC 19762, Information technology — Automatic identification and data capture (AIDC) techniques —
Harmonized vocabulary
AIM Extended Channel Interpretations (ECI), Part 1: Identification Schemes and Protocols
AIM Extended Channel Interpretations (ECI), Part 2: Registration Procedure
AIM Extended Channel Interpretations (ECI), Part 3: Register
3 Terms, definitions, symbols and functions
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 19762 and the following apply.
© ISO/IEC 2024 – All rights reserved
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1.1
bullseye
set of concentric square rings used as the finder pattern in Aztec Code
3.1.2
checkword
codeword which is included in a symbol for either error correction or error detection, or both
3.1.3
dataword
codeword which is part of the data message encoded in a symbol
3.1.4
domino
2-module sub-structure of the symbol character in Aztec Code which is the elemental entity used in graphical
encoding of the symbol
3.1.5
mode message
short, fixed-length, error-corrected subsidiary message within an Aztec Code symbol which directly encodes
the symbol’s size and data message length
3.2 Symbols and functions
3.2.1 Mathematical symbols
For the purposes of this document, the following mathematical symbols apply.
B the number of bits in each codeword
C the symbol capacity in number of bits
b
C the symbol capacity in number of codewords
w
D the number of data (message) codewords in the symbol
K the number of error correction codewords in the symbol, equal to C − D
w
L the number of data layers (1 to 32) in the symbol, defining its size
m the symbology identifier modifier value
x a general variable used to express error correction polynomials
(x,y) Cartesian coordinates within the module grid
3.2.2 Mathematical functions and operations
For the purposes of this document, the following mathematical functions and operations apply.
© ISO/IEC 2024 – All rights reserved
abs() is the absolute value function
div is the integer division operator
max(a,b) is the greater of a and b
mod is the remainder after integer division
4 Symbology characteristics
4.1 Basic characteristics
Aztec Code is a two-dimensional matrix symbology with the following basic characteristics:
a) Encodable character set:
1) All 8-bit values can be encoded. The default interpretation shall be:
i) values 0 to 127 in accordance with ISO/IEC 646 International Reference Version (IRV), i.e. all
128 ASCII characters;
ii) values 128 to 255 in accordance with ISO/IEC 8859-1. These are referred to as extended ASCII.
This interpretation corresponds to Extended Channel Interpretation (ECI) ECI 000003.
Additional characters may be encoded using the ECI capabilities.
2) Two non-data characters can be encoded: FNC1 for compatibility with some existing applications
and ECI escape sequences for the standardized encoding of message interpretation information.
b) Representation of data: A dark module is a binary one and a light module is a binary zero.
c) Symbol size:
1) The smallest Aztec Code symbol is 15 × 15 modules square, and the largest is 151 × 151.
2) No quiet zone is required outside the bounds of the symbol.
d) Data capacity (at recommended error correction level):
1) The smallest Aztec Code symbol encodes up to 13 numeric or 12 alphabetic characters or 6 bytes
of data.
2) The largest symbol encodes up to 3832 numeric or 3067 alphabetic characters or 1914 bytes of data.
e) Selectable error correction:
1) User-selectable, from 5 % to 95 % of the data region, with a minimum of 3 codewords.
2) Recommended level is 23 % of symbol capacity plus 3 codewords.
f) Code type: Matrix.
g) Orientation independent: Yes.
4.2 Summary of additional features
The following summarizes additional features that are inherent or optional in Aztec Code:
a) Reflectance Reversal (Inherent): Though Aztec Code symbols are always shown and described in this
document with the finder’s centre dark and with dark modules encoding binary 1 s throughout, symbols
© ISO/IEC 2024 – All rights reserved
exhibiting the opposite reflectance characteristics are easily autodiscriminated and decoded with the
standard reader.
b) Mirror Image (Inherent): Images which contain an Aztec Code symbol in mirror reversal, either because
they are obtained using a reflected optical path, a reversed scan direction, or from behind through a
clear substrate, are easily autodiscriminated and decoded with the standard reader.
c) Extended Channel Interpretation (Optional): The ECI mechanism enables characters from various
character sets (e.g. Arabic, Cyrillic, Greek, Hebrew) and other data interpretations or industry-specific
requirements to be represented.
d) Structured Append (Optional): Structured Append allows files of data to be represented logically and
continually in up to 26 Aztec Code symbols. The symbols may be scanned in any sequence to enable the
original data to be correctly reconstructed.
e) Reader Initialization Symbols (Optional): A distinct format of Aztec Code symbol is available for use in
bar code menus for reader initialization. The encoded message in these special symbols is never passed
on to an application.
f) Aztec “Runes” (Optional): a series of 256 small, machine-readable marks compatible with Aztec Code
are available for special applications. Normative Annex A defines Aztec “Runes”.
5 Symbol description
5.1 Basic Aztec Code properties
Aztec Code symbols are nominally square, made up of square modules on a square grid, with a square
bullseye pattern at their centre. Figure 1 shows two representative Aztec Code symbols, a small 1-layer
symbol on the left which encodes 12 digits with 47 % error correction, and a larger 6-layer symbol on the
right which encodes 168 text characters with 30 % error correction.
Figure 1 — Representative Aztec Code symbols
These symbols illustrate the two basic formats of Aztec Code symbols: on the left is a “compact” Aztec Code
symbol, visually characterized by a 2-ring bullseye, useful for encoding shorter messages efficiently. On the
right is a “full-range” Aztec Code symbol, visually characterized by a 3-ring bullseye, which supports much
larger symbols for longer data messages. Since encoders can autoselect and decoders auto discriminate
between the two formats, a seamless transition is achieved to cover the full spectrum of applications.
5.2 Symbol structure
5.2.1 Aztec code layout
The underlying structure of a compact Aztec Code symbol is shown in Figure 2, and that of a full-range Aztec
Code symbol is shown in Figure 3. In both cases, the Aztec Code symbol has at its centre a Core Symbol
which is then surrounded by data fields on all four sides.
© ISO/IEC 2024 – All rights reserved
Key
1 layer 1
2 layer 2
3 layer 3
4 layer 4
5 mode bits
Fixed structures:
6 finder pattern
7 orientation patterns
Variable structures
8 mode message
9 data layers
Figure 2 — Structure of a “compact” Aztec Code symbol
© ISO/IEC 2024 – All rights reserved
Key
1 layer 1
2 layer 2
3 layer 3
4 layer 4
5 layer 5
6 layer 6
7 mode bits
Fixed structures
8 reference grid
9 finder pattern
10 orientation patterns
Variable structures
11 mode message
12 data layers
Figure 3 — Structure of a “full-range” Aztec Code symbol
5.2.2 Core Symbol
5.2.2.1 Core Symbol position and content
The Core Symbol, always square and at the exact centre of an Aztec Code symbol, consists of a finder pattern,
orientation patterns, and a mode message. This core covers an 11 × 11 module area in compact symbols and
© ISO/IEC 2024 – All rights reserved
a 15 × 15 module area in full-range symbols. It is called the Core “Symbol” because it must be successfully
found and decoded before decoding can proceed into the surrounding data fields.
5.2.2.2 Finder pattern
The finder pattern in Aztec Code is a set of concentric square rings. Centred on a single dark module, there
is a ring of light modules surrounded by a larger ring of dark modules, and so forth outward to a second
9 × 9 module dark ring in compact symbols and to a third 13 × 13 module dark ring in full-range symbols.
5.2.2.3 Orientation patterns
Four 3-module chevron-shaped orientation patterns are located at the corners of the finder pattern. The
upper left-hand pattern is all dark and the lower left-hand pattern is all light, while the upper righthand
pattern has two modules dark and the lower right pattern has just one module dark, as shown in
Figures 2 and 3.
5.2.2.4 Mode message
The single layer of bits adjoining the finder pattern, excluding the orientation patterns and in full-range
symbols also excluding the centre bit along each side (which is part of the reference grid), comprises an
error-corrected mode message wrapped in a clockwise direction starting from the upper left corner. This
message explicitly encodes both the number of data layers in the overall symbol (and thus its size) and the
number of datawords in those layers, the rest being error correction checkwords for that message. Encoding
details for the mode message are given in 7.2.
5.2.3 Data fields
The data fields symmetrically surround the Core Symbol with one or more data layers. In full-range symbols,
a reference grid also threads throughout the data fields.
5.2.3.1 Reference grid
The reference grid, clearly evident in Figure 3, is a ladder-like extension of the dark/light periodicity in the
finder along every 16th row and column of the symbol, extending to the limit of the data fields. Its regular
structure provides outlying reference points often needed to accurately map the data field in the larger full-
range symbols. Compact Aztec Code symbols, which are of limited size, have no reference grid structure.
Other matrix symbology specifications name reference grid as clock track.
5.2.3.2 Data layers
The message data themselves plus their error correction words are laid into 2-module thick layers, spiralling
clockwise from the upper left corner of the Core Symbol outward, and in full-range symbols necessarily
skipping over module positions occupied by the reference grid. Compact Aztec Code symbols can have from
one to four data layers, while full-range Aztec Code symbols can have from one up to 32 data layers. Details
of the message encoding, codeword formation, error correction encoding, and the final laying of codewords
into the data layers are given in 7.3.
5.3 Symbol character structure and sequence
In order to enhance Reed-Solomon error correction performance, the codewords, and thus the symbol
characters, vary in size from 6-bits up to 12-bits depending on the overall symbol size, as illustrated in
Figure 4.
© ISO/IEC 2024 – All rights reserved
Key
1 in 2 to 3-layer symbols
2 in 3 to 8-layer symbols
3 in 9 to 22-layer symbols
4 in 23 to 33-layer symbols
5 MSB (most significant bit)
6 typical domino
Figure 4 — Symbol character structure
While spiralling around the core, turning corners and occasionally skipping across the reference grid, the
symbol characters’ actual shapes vary widely. However, if they are regarded as sequences of “dominos”
( each 2-modules tall by 1-module wide), then the sequence of symbol characters becomes a sequence of
dominos whose placement is highly systematic throughout the data fields, and thus easy to place during
encoding and easy to map during decoding. Figure 5 shows how the sequence of dominos is positioned as it
turns corners and transitions between data layers.
Key
1 MSB
2 typical domino
Figure 5 — “Domino” layout and sequencing
© ISO/IEC 2024 – All rights reserved
The sequence of codewords that spirals outward from the Core Symbol is in fact reversed from its natural
order: the first codeword in the spiral is the last Reed-Solomon checkword, followed then by the immediately
preceding checkword, and so forth through the check words and then through the message codewords,
until the final codeword in the outermost data layer is the first codeword of the encoded message. This
arrangement enhances error correction by locating the data codewords (which have erasure detection
because data codewords with all zeros or all ones are illegal) near the symbol’s perimeter where erasures
are more likely to occur.
5.4 Symbol size and capacity
Table 1 lists the overall size and capacities of the different sized Aztec Code symbols.
The data capacities shown are based on the recommended error correction levels (see 4.1.e). They represent
approximate limits because the message encoding efficiency depends in a detailed way on message content
and because the error correction level is user adjustable.
Table 1 — The size and capacities of Aztec Code symbols (23 % error correction level)
# of Data Symbol Codeword Symbol Bit Symbol Data Capacities
Layers Size (in x) Count x Size Capacity Digits Text Bytes
a
1 15 × 15 17 × 6 102 13 12 6
1 19 × 19 21 × 6 126 18 15 8
a
2 19 × 19 40 × 6 240 40 33 19
2 23 × 23 48 × 6 288 49 40 24
a
3 23 × 23 51 × 8 408 70 57 33
3 27 × 27 60 × 8 480 84 68 40
a
4 27 × 27 76 × 8 608 110 89 53
4 31 × 31 88 × 8 704 128 104 62
5 37 × 37 120 × 8 960 178 144 87
6 41 × 41 156 × 8 1248 232 187 114
7 45 × 45 196 × 8 1568 294 236 145
8 49 × 49 240 × 8 1920 362 291 179
9 53 × 53 230 × 10 2300 433 348 214
10 57 × 57 272 × 10 2720 516 414 256
11 61 × 61 316 × 10 3160 601 482 298
12 67 × 67 364 × 10 3640 691 554 343
13 71 × 71 416 × 10 4160 793 636 394
14 75 × 75 470 × 10 4700 896 718 446
15 79 × 79 528 ×10 5280 1008 808 502
16 83 × 83 588 × 10 5880 1123 900 559
17 87 × 87 652 × 10 6520 1246 998 621
18 91 × 91 720 × 10 7200 1378 1104 687
19 95 × 95 790 × 10 7900 1511 1210 753
20 101 × 101 864 × 10 8640 1653 1324 824
21 105 × 105 940 × 10 9400 1801 1442 898
22 109 × 109 1020 × 10 10200 1956 1566 976
23 113 × 113 920 × 12 11040 2116 1694 1056
24 117 × 117 992 × 12 11904 2281 1826 1138
a
“compact” symbol; the rest are “full-range” symbols.
NOTE: Full range symbols with 1, 2, or 3 layers are useful only for reader initialization.
© ISO/IEC 2024 – All rights reserved
TTabablele 1 1 ((ccoonnttiinnueuedd))
# of Data Symbol Codeword Symbol Bit Symbol Data Capacities
Layers Size (in x) Count x Size Capacity Digits Text Bytes
25 121 × 121 1066 × 12 12792 2452 1963 1224
26 125 × 125 1144 × 12 13728 2632 2107 1314
27 131 × 131 1224 × 12 14688 2818 2256 1407
28 135 × 135 1306 × 12 15672 3007 2407 1501
29 139 × 139 1392 × 12 16704 3205 2565 1600
30 143 × 143 1480 × 12 17760 3409 2728 1702
31 147 × 147 1570 × 12 18840 3616 2894 1806
32 151 × 151 1664 × 12 19968 3832 3067 1914
a
“compact” symbol; the rest are “full-range” symbols.
NOTE: Full range symbols with 1, 2, or 3 layers are useful only for reader initialization.
6 General encodation procedures
The following steps are required to convert data into the encoded form represented in an Aztec Code symbol.
The following clauses of this document specify all the rules and procedures. An encoding example is shown
in Annex G.
a) Data from a 256-character set may be encoded in Aztec Code. The input message is presented in a
stream of byte values reading from left to right. Special FNC1 or ECI flag characters may be inserted at
any point in the stream.
b) Each message character is translated into 4, 5, or 8 bits, preceded by additional 4- or 5-bit shift and latch
codes as needed, forming a long continuous data bit stream.
c) The minimum number of bits to be encoded is computed by taking the length of the data bit stream
and adding as many bits as needed to reach either the default or user-specified error correction
percentage. From this calculation, the format and minimum size (number of data layers L) of the symbol
is selected using Table 1. This in turn establishes both the codeword size B and overall symbol capacity
in codewords C .
w
d) The data bit stream is laid into codewords, systematically avoiding the formation of any codewords
containing all 0’s or all 1’s, thus creating D message codewords.
e) The number K of checkwords becomes C minus D. Systematic Reed-Solomon encoding, based on a
w
B
Galois Field of size 2 and using a generator polynomial of order K, is employed to generate K additional
check codewords which are appended to the sequence of message codewords.
f) The binary values of L and D are formed into a mode message, and systematic Reed-Solomon encoding
based on GF(16) is employed to generate additional check bits.
g) Graphically, the L-layer symbol is constructed by placing modules first for the fixed structures of the
finder, orientation patterns, and (if full-range) reference grid, then for the mode message wrapping
around the finder, and finally for the spiralling layers of dominos which constitute the sequence of
datawords and checkwords taken in reverse order.
© ISO/IEC 2024 – All rights reserved
7 Symbol structure
7.1 Fixed pattern structures
7.1.1 Fixed pattern types
An Aztec Code symbol contains three types of fixed pattern: the finder, orientation bits, and, if full-range,
a reference grid. These are all shown in Figures 2 and 3. Their specification is facilitated by regarding the
...
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