PDF 417 Stacked Barcode
The CVL ID tools include a PDF417 decoder. PDF417 is a multirow, variable-length 2D symbology that offers high data capacity and error correction capability. The current tool expects the symbol to be the predominant feature in the image.
The following is an example of a typical PDF417 symbol and its structure.
PDF417 Symbol Structure
Every PDF417 symbol contains a minimum of 3 rows to a maximum of 90 rows. Each row consists of the following elements:
- Leading Quiet zone
- Start pattern
- Left row indicator symbol character
- One to thirty data symbol characters
- Right row indicator symbol character
- Stop pattern
- Trailing Quiet zone
A symbol character consists of seventeen modules arranged into four bars and four spaces. Each symbol character represents a value in the range of 0 to 928. These symbol character values are often referred to as codewords (not to be confused with the term codewords used in error correction literature).
Because the number of rows is variable, and rows are of variable length in the number of symbol character columns they contain, the height/width proportion, or aspect ratio, of a PDF417 symbol can be varied to suit spatial requirements for printing. However, the number of symbol characters in all rows of a given symbol must be the same.
The data region of a PDF417 symbol is the central area of codeword columns between the left row indicator column and the right row indicator column. The first (upper left) codeword of the data region is the symbol length descriptor. Its value indicates the total number of codewords in the data region, including the symbol length descriptor itself, but excluding the error correction codewords. The remaining codewords in the data region (including the data codewords, pad codewords, and error correction codewords, in that order) are arranged with the most significant codeword adjacent to the symbol length descriptor, and are read from left to right, top to bottom. The total number of codewords in the data region of a single PDF417 symbol cannot exceed 928.