PDF417 barcode in a PDF

Where the symbol comes from

This API renders HTML to PDF. It does not generate barcodes, so the PDF417 symbol itself is produced by an encoder in your own stack and placed in the markup, either as inline SVG or as a data URI. That split matters more than it sounds: the encoders are mature and correct, and almost every barcode that will not scan failed for a layout reason rather than an encoding one. Everything below is about the layout half.

What it can encode

Up to roughly 1,850 text characters, 2,710 digits or 1,100 bytes in a single symbol, depending on the compaction mode the encoder picks. The name comes from the structure: each codeword is 17 modules wide, made of four bars and four spaces.

The check digit, and who computes it

Error correction rather than a check digit, at nine selectable levels from 0 to 8. Higher levels add codewords and recover more damage. Level 5 is a common default for a document that will be handled; a symbol on a card that gets carried in a wallet justifies more.

Size and quiet zone

The two measurements that decide whether a scanner accepts the symbol, and the two most often lost when a design is adjusted to fit.

• X-dimension: The module width, commonly 0.25mm or above, with a row height of at least three times the module width. The aspect ratio is chosen by the encoder from a target number of columns, so the same data can be a wide short symbol or a narrow tall one.
• Quiet zone: 2 modules on all four sides, which is small compared with a linear symbology and is still frequently omitted. A PDF417 laid flush against a printed rule fails.

Where it is used

• driving licences and identity documents, where the symbol carries the whole record
• airline boarding passes, in the format the industry standard defines
• shipping labels where a large payload has to travel with the parcel
• any application that has to work offline, because the data is in the symbol rather than behind a lookup

Placing it in the markup

The quiet zone is padding on the container rather than part of the encoder's output, so it survives a change of encoder. Dimensions are in millimetres, because a bar width is a physical measurement and a percentage makes it depend on whatever the container happens to be.

<figure class="pdf417">
  <img src="data:image/svg+xml;base64,PHN2ZyB4bWxucz0i..." alt="Boarding pass data">
</figure>

<style>
.pdf417 {
  margin: 0;
  /* 2 modules of quiet zone on all four sides. Small, and still the
     thing most often left out because the symbol looks finished. */
  padding: 1.5mm;
  background: #fff;
  width: max-content;
  print-color-adjust: exact;
  -webkit-print-color-adjust: exact;
}
.pdf417 img {
  /* Absolute width AND height. A stacked symbology has a row height
     that matters as much as the module width, and letting one be auto
     while the other is fixed distorts the aspect. */
  width: 76mm;
  height: 23mm;
  display: block;
  image-rendering: crisp-edges;
}
</style>

What goes wrong on paper

Letting the aspect ratio drift. PDF417 rows have a defined height relative to the module width, and a symbol squashed vertically to fit a strip on a boarding pass loses the row separation the decoder relies on. Set both dimensions, and if the symbol does not fit, re-encode it with a different column count rather than scaling what you have.

First thing to check when it will not scan

Check whether the symbol was rasterised. PDF417 has fine horizontal structure, and a bitmap resampled at print resolution merges adjacent rows in a way that looks fine at a glance and destroys the decode. Encode to SVG and let the PDF carry it as vector.

Vector, not a bitmap

Encode to SVG wherever the encoder offers it. A rasterised barcode is resampled when the PDF is printed, and at 203 or 300 dots per inch the bar edges land between printer dots, so the ratio of bar to space drifts by a fraction of a millimetre. That fraction is the whole tolerance. An SVG stays vector inside the PDF and is rendered at the printer's own resolution, which removes the entire failure mode. Where a bitmap is unavoidable, generate it at the final physical size and set image-rendering so nothing smooths the edges.

Frequently asked

Other symbologies

Codes of the same kind, and one from each of the other kinds.