Aztec Code |
Aztec is a two-dimensional general-purpose matrix symbology designed to have a higher accuracy than other two-dimensional symbologies. A symbol can hold up to 3832 digits, or 3067 characters, or 1914 bytes. The size, and the degree of error correction, can be fixed at label-design-time or set to change automatically in response to the length of the data. Printing White-on-Black is an option.
The Character Set
The character set consists of all 255 ASCII characters (digits, 0-9, text, binary data), the FNC1 (^1) symbol, and the Flag 7 (^7) symbol. A Flag 7 followed by six digits, ^7nnnnnn, represents an ECI (Extended Channel Interpretation Protocol) value, where nnnnnn is the 6-digit ECI number. For example, ^7000009 represents ECI value 9. ECI protocol values have four types of interpretations:
As identifiers of international character sets (codepages)
As control information for structured append in unbuffered mode
As information for encryption or compaction or other general purposes
As user defined information
|
|
|
The Symbology Structure
As a finder pattern, the barcodes have a square "bullseye" structure in the center with alternating black and white, one-module wide, square rings and a center 1-by-1 module square (which is black unless the White-on-Black option is being used). The number of rings varies with the size of the barcode (see below).
Immediately outside the outermost ring is a one-module wide mode-and-orientation layer. At each corner of this layer are chevron-shaped orientation patterns consisting of three (1-by-1 module) squares that bend around the corners of the finder pattern (see the diagram below). The first is stipulated to be all black. At the second corner, moving clockwise around the finder pattern, the orientation pattern is a single white followed by two black modules. The third is a black followed by two whites. The last is all white.
In the same layer, between the orientation patterns is a mode message that specifies how many total data layers (see below) are in the barcode and the length of the data (not including check characters).
The remainder of the barcode consists of one or more two-module wide layers containing data and check characters. These layers are read in a clockwise direction. The first data layer begins immediately beside the first orientation pattern, the all black one. (In this context, "beside" means that if the barcode is positioned so that the first orientation pattern is to the upper left, then the first data layer begins immediately above the orientation pattern — see the diagram below). This first data layer moves clockwise around the mode and orientation layer and ends beside its own starting edge. Each additional data layer begins immediately beside the ending edge of the preceding layer and ends beside its own starting edge. But note that the reading direction of the layer at its end is perpendicular to the reading direction of the next layer at its start (see the diagram below). Accordingly, a barcode scanner can read the data layers as a continuous spiral.
There are two broad groups of Aztec barcodes:
Compact: A Compact Aztec Barcode has two white and two black finder pattern rings (in addition to the center square), 1 to 4 data layers, and no reference grid.
Full: A Full Aztec Barcode has three white and three black finder pattern rings (in addition to the center square), 4 to 32 data layers, and a reference grid. The latter is a set of one-module wide rows of alternating one-module black and white squares. One row bisects the entire barcode (except the finder pattern area) beginning and ending at the midpoint of the outermost edge of the outermost layer. A second row is identical to, but perpendicular to, the first. In addition, there are rows immediately outside all four sides of every fourth layer (except the outermost layer). Each of these rows, however, continues completely across the barcode rather than wrapping around as the data layers do.
|
|
An Aztec barcode with four data layers can be structured as either a Compact or a Full barcode. See also the note at the end of the Dimensions section below. |
Since the barcodes are read from the inside out, there is no quiet zone.
The Dimensions
There can be 1 to 32 data layers, but since there are two sizes of 4-layer symbols there are a total of 33 different sizes of Aztec barcodes. The smallest is 15-by-15 modules while the largest is 151-by-151. The barcodes are always squares.
