PDF417
PDF417 is a stacked linear barcode format used in a variety of applications, including transportation, identification, and inventory management. Developed by Symbol Technologies in 1991, the "PDF" in PDF417 stands for Portable Data File. The "417" signifies that each pattern in the code consists of 4 bars and 4 spaces, and that each pattern is 17 modules long.
PDF417 barcodes can encode significantly more data per unit area than traditional linear (1D) barcodes. This is because PDF417 is essentially a miniature, machine-readable data file. It's composed of stacked rows of barcode symbols, each row acting as a separate "layer" of information.
Key characteristics of PDF417 include:
- High Data Density: PDF417's stacked structure enables it to store a large amount of data compared to 1D barcodes. It can encode alphanumeric characters, text, numbers, files, and actual data.
- Error Correction: PDF417 incorporates error correction capabilities using Reed-Solomon error correction, allowing the barcode to be read even if partially damaged or obscured. The level of error correction can be adjusted during barcode creation, trading off data capacity for increased robustness.
- Variable Length: Unlike some fixed-length barcodes, PDF417 can be designed to accommodate variable lengths of data. The height and width of the barcode can be adjusted to suit the application's needs and the amount of data being encoded.
- Structured Append: PDF417 supports structured append, allowing a single piece of data to be split across multiple barcodes. This is useful for encoding very large amounts of information. Each barcode in the sequence contains information about its position within the sequence.
The structure of a PDF417 barcode includes a start pattern, left row indicator, data codewords, optional error correction codewords, right row indicator, and stop pattern. The data codewords represent the actual encoded data, while the error correction codewords allow for data recovery in case of damage. The row indicators provide information about the row number and other metadata.
PDF417 is standardized as ISO/IEC 15438.