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PDF417 and 2D Symbology

Thursday, December 08, 2011

As GS1-128 (formerly UCC-128) label technology expands, the PDF417 symbol is being integrated into labels used on cartons, pallets and containers of all sizes to convey large amounts of data that can be interpreted by one pass of a scanner. This information allows for specialized shipping, receiving, stocking and inventory functions to be incorporated with an increase in accuracy and a decrease in errors and exceptions. You may need to put a part number, a purchase order number, a vendor number, and other various item data all into one bar code. The problem is how to do this in a way that is easily understood, and will be compatible with the systems used by your suppliers and customers.

The PDF417 is a variable length, multi row 2D symbol providing high data capacity which can be encoded to include 1100 bytes, 1800 characters or 2710 digits. The PDF417 also includes various levels of error correction capabilities allowing for slightly damaged labels to be scanned and decoded correctly using linear scanners, laser scanners or two dimensional scanners.

Symbol Structure

A typical PDF417 symbol contains 3 to 90 rows. Each row contains from left to right:

• Leading quiet zone
• Start Pattern
• Left row indicator symbol character
• 1 to 30 data symbol characters
• Right row indicator symbol character
• Trailing quiet zone

There is a standard structure used to build the data contained in the symbol that is similar to an EDI Transaction envelope with ANSI MH10.8.3, format “06” being the most common. The typical symbol starts with a header that informs the scanner that the bar code follows a specific format. Next in line are the data fields incorporated into the bar code separated by a defined delimiter. Last is a trailer indicating the end of the bar code. The PDF417 shown above contains the following data when scanned:
“[)>06 123456 (P) A93387Y665 (I) Protect From Freezing and Extreme Heat and Humidity (V) 22873445A9984657555 1+2+3+4+5+6 = 21 It was a dark and stormy night (ST) 987654321 “

Symbol Character Encoding

Each PDF417 symbol character consists of four bars and four spaces which totals 17 modules in width. Each bar and space can be from 1 to 6 modules in length. In theory it has 9x020 patterns. Each set of 929 patterns is called a cluster (character set). PDF417 only uses cluster number 0, 3 and 6.

Row Encoding

Each row uses character patterns from a single cluster. Adjacent rows use different clusters in the sequence 0, 3, 6, 0, 3, 6: Cluster number = (row number -1) mod 3) * 3. Each row starts with a left row indicator and ends with a right row indicator. These row indicators are characters based on row number, total number of rows, number of columns and the error correction level.

Error Correction Capacity

Each PDF417 symbol contains 2 to 512 error correction code words corresponding to error correction level 0 (lowest) to 8 (highest). Auto Correction allows the software to determine the level of correction to be used based on the data encoded.

Printing Considerations

A high resolution thermal transfer printer (dpi >= 200) will normally produce symbols readable by most scanners. At 1 EDI Source, Inc., we provide label and printing resources for a wide variety of industries and applications. We can provide the technology and hardware to meet all of your label design and printing needs now and in the future.

Page Title: EDI Tips & News | 1 EDI Source, Inc. - PDF417 and 2D Symbology