PDF417 Bar Codes
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The PDF417 bar code is a stacked bar code that can be used to encode larger amounts of information across multiple codes. Each pattern in an individual bar code consists of exactly 4 bars and 4 spaces, and each pattern is 17 units long. This is where the number 417 comes from. The PDF417 can encode up to 1,800 ASCII characters per bar code or up to 1,100 binary characters per symbol. It is often used on driver's licenses, and can also be used by postage meters to encode the proper amount of postage, as well as on FedEx packages.
Specifications: The PDF417 begins with a quiet zone or blank space, followed by a start pattern, to signify the beginning of the bar code. After that is a left row indicator, which has specific information about the data included in the row and how to read it. Then between 1 and 30 code words of data are encoded, followed by a right row indicator, containing more information about the row. Finally, the stop pattern indicates the end of the bar code, followed by another quiet zone.
Advantages: The PDF417 bar code can encode any ASCII character. You can stack as many of the codes on top of one another as you like, theoretically allowing you to encode a limitless amount of data. Also, the bar code includes a check digit in each individual bar code, to guard against errors.
Disadvantages: While you theoretically can encode as much information as you like in multiple stacked codes, eventually it would grow bulky if you tried to encode too much.