| PDF417
s a multi-row, variable-length symbology
offering high data capacity and error-correction capability. PDF417 can
be scanned by linear PDF417 barcode scanners, rastering
laser scanners, or
two-dimensional imaging devices. One PDF417 symbol is capable of
encoding more than 1100 bytes, 1800 ASCII characters, or 2700 digits,
depending on the selected data compaction mode.
Every PDF417 symbol is composed of
stack of rows, from a minimum of 3 to a maximum of 90 rows.
Each PDF417 row contains start and stop patterns, left and right
row indicators, and from one to thirty data symbol characters.
Since both the number of rows and their length are selectable
when printed, the aspect ratio of a PDF417 symbol can be varied
to suit spatial requirements for printing.
A PDF417 symbol character
consists of seventeen modules arranged into four bars and four
spaces. The entire set of symbol characters is divided
into three mutually exclusive encodation sets, or "clusters".
Each cluster encodes the 929 available PDF417
symbol character values, or codewords, with distinct bar-spaces
patterns so that one cluster cannot be confused with another.
Because any two adjacent rows use different clusters, the
decoder can utilize data from scans that cross rows while
decoding a PDF417 symbol.
By adding
error correction codewords to the data message, PDF417 supports
correction of lost or missing data. Each PDF417 symbol requires
two error correction codewords for error detection. In
addition, up to 510 codewords of error correction can be added
when printing the symbol. This allows for decoding
security that mathematically is many orders of magnitude
stronger than that of bar codes with simple check characters.
PDF417 offers
three data compaction modes. Each mode defines a
conversation or mapping between codeword sequences and byte
sequences. The three modes are Text Compaction mode, Byte
Compaction mode, and Numeric Compaction mode.
The
interpretation of the byte sequences encoded by a compaction
mode is determined by the Global Label Identifier (GLI). A
GLI is a special codeword sequence which activates a set of
interpretations. The implementation of GLIs enables PDF417
to encode international character sets, and industry - and
user-defined character sets, as well as ASCII |
Marco PDF417 provides a
means for creating a distributed representation of files too
large to be represented by a single PDF417 symbol.
Marco PDF417 symbols differ from ordinary PDF417 symbols in
that they contain additional control information used to
support this distributed representation. This allows a
decoder to make use of this information to correctly
reconstruct and verify the file, independent of the symbol
scanning order.
In a relatively clean
environment in which damage to the label is unlikely,
Truncated PDF417 can be used. This version omits the
right row indicator and simplifies the stop pattern into a
single module width bar. This reduces the non-data
overhead, with some trade-off in robustness, or the ability
to withstand degradation. Truncated PDF417 is fully
reader-compatible with standard PDF417.
Table below summarized
PDF417's characteristics:
|
Characteristics
of PDF417 |
|
|
Encode
Character Set ..................... All 128
ASCII characters
All 128 Extended ASCII Characters
8-Bit Binary Data
Up to 811,800 Different Character Sets or
interpretations |
Code
Type
...........................................
Continuous, Multi-row
Character Self Checking
......................................................
Yes
Symbol Size:
Height
..................................................
Variable (3 to 90 Rows)
Width
....................................................
Variable (90X to 583X)
Bidirectional Decoding
.......................................................
Yes
Error Correction Characters
...................................... .. 2
to 512
Maximum Data Characters per Symbol
.................. 1850 texts
(at error correction level 0)
2710 digits
1108 bytes
Additional Features ... Selectable Levels of
Error Correction
Can Utilize Scans that Cross Rows
Additional Options
..........................................
Macro PDF417
Global Label Identifiers
Truncated PDF417 |
|
Symbol
Structure
Each PDF 417
symbol consists of a stack of vertically aligned rows framed
by clear areas called quiet zones.
|
