Symbology Characteristics

 

Basic Characteristics

 

‘PDF417' is a multi-row symbology with the following basic characteristics:

Encodable character set:

Text Compaction mode permits all printable ASCII characters to be encoded, i.e. values 32 - 126 inclusive in accordance with ISO/IEC 646, as well as selected control characters.

Byte Compaction mode permits all 256 possible 8-bit byte values to be encoded.  This includes all ASCII characters value 0 to 127 inclusive and provides for international character set support.

Numeric Compaction mode permits efficient encoding of long numeric data digit strings.

Up to 811 800 different character sets or data interpretations.

Various function codewords for control purposes.

Symbol character structure:

n, k, m symbology of 17 modules (n), 4 bar elements (k), with the largest element 6 modules wide (m). 

Maximum number of data characters:

Per symbol (at error correction level 0) 925 data codewords which can encode:

Text Compaction mode:

1850 characters (at 2 data characters per codeword).

Byte Compaction mode:

1108 characters at 1.2 data characters per codeword.

Numeric Compaction mode:

2710 characters at 2.93 data characters per codeword.

Symbol size:

Number of rows: 3 to 90.

Number of columns: 1 to 30.

Width in modules: 90X to 583X including quiet zones.

Maximum codeword capacity: 928 codewords.

Maximum data codeword capacity: 925 codewords.

Since the number of rows and columns are selectable, the aspect ratio of a ‘PDF417' symbol may be varied when printing to suit the spatial requirements of the application.

Selectable error correction:

A user may define one of 9 error correction levels labeled levels 0 to 8.  All error correction levels, except Level 0, not only detect errors but also can correct erroneously decoded or missing codewords. There are 2 (Level 0) to 512 (Level 8) codewords per symbol.

Non-data overhead:

1.         Per row: 73 modules, including quiet zones.

2.         Per symbol: a minimum of 3 additional codewords, represented as symbol characters.

Code type:

Continuous, multi-row two-dimensional.

Character self-checking:

Yes.

Bi-directionally decodable:

Yes.

Additional Features

The following are additional features, which are inherent or optional in ‘PDF417':

Data Compaction:

Inherent:  These schemes are defined to compact a number of data characters into codewords.  Generally data is not directly represented on a one character for one codeword basis.

Extended Channel Interpretations: 

Optional:  These mechanisms allow up to 811,800 different data character sets or interpretations to be encoded.

Macro ‘PDF417':

Optional:  This mechanism allows files of data to be represented logically and consecutively in a number of ‘PDF417' symbols.  Up to 99 999 different ‘PDF417' symbols can be so linked or concatenated and be scanned in any sequence to enable the original data file to be correctly reconstructed.

Edge to edge decodable: 

Inherent:  As an n, k symbology ‘PDF417' can be decoded by measuring elements from edge to similar edge.

Cross row scanning:

Inherent:  The combination of the following three characteristics in ‘PDF417' that allow a single linear scan to cross a number of rows and achieve a partial decode of the data so long as at least one complete symbol character per row is decoded into its codeword.  The decoding algorithm can then place the individual codewords into a meaningful matrix.

Being synchronized horizontally, or self clocking

row identification

being vertically synchronized, by using the cluster values to achieve local row discrimination

Error correction:

Inherent:   A user may define one of 9 error correction levels.  All error correction levels, except Level 0, not only detect errors but can correct erroneously decoded or missing codewords.