PDF417 Barcode FAQ & Tutorial

INDEX:

• PDF417 Overview
  • Error Correction Levels
  • X and Y Dimensions
  • Row and Column Limits
  • Truncated PDF417
• Generating and Printing PDF417 Barcodes
  • Measuring X and Y Dimensions
  • Compaction Modes and Amount of Data Encoded
  • Creating Small Symbols
  • Encoding Functions
  • Formatting Data for FedEx® Specifications
  • Encoding International and Extended Characters
• Verifying
• Reading
• Macro-PDF417

  -------- PDF417 Products -------- Font and Encoders .NET Windows Forms Control ActiveX Control ASP.NET Server Control ASP Server for IIS Barcode Label Software Crystal Reports Java Class, Applet & Servlet Image Generator Microsoft Access Native JavaScript Online Generator Reporting Services Windows Mobile XML Webservice Barcode Scanners Barcode Printers

  • Macro PDF Example
  • Macro PDF Properties
• PDF417 Barcode Scanners

Large amounts of text and data can be stored securely and inexpensively when using the PDF417 barcode symbology. The printed symbol consists of several linear rows of stacked codewords. Each codeword represents 1 of 929 possible values from one of three different clusters. A different cluster is chosen for each row, repeating after every three rows. Because the codewords in each cluster are unique, the scanner is able to determine what line each cluster is from.

PDF417 Error Correction Levels

PDF417 uses Reed Solomon error correction instead of check digits. This error correction allows the symbol to endure some damage without causing loss of data. AIM standards recommend a minimum error correction level of 2. The error correction level depends on the amount of data that needs to be encoded, the size and the amount of symbol damage that could occur. The error correction levels range from 0 to 8. The chart below indicates the number of error correction codewords that are added to the printed symbol and AIM recommendations for the EC level.

Fig. 1: AIM recommended EC levels

X and Y Dimensions

The X dimension is the width of the narrowest bar in a printed codeword. The Y dimension is the height of each row within the PDF417 symbol. The PDF417 barcode is usually printed at an X to Y ratio of 1:2 to 1:5, with 1:3 being the most popular. By lowering the ratio, a significant amount of space can be saved; however, some scanners cannot read X to Y ratios of less than 1:3. Most scanners, such as the IDAutomation PDF417 USB Scanner, read PDF417 barcodes well at 1:3. When creating symbols with more than 10 columns, IDAutomation recommends using a ratio of 1:4 or 1:5.

Row and Column Limits

The number of rows and columns can be selected, allowing the symbol to be created in various forms. However, the PDF417 barcode symbol is limited to 30 columns and 90 rows. Keep in mind when selecting columns, only the number of data columns in the symbol are being selected. The normal PDF417 barcode symbol has two row start columns and two row stop columns. Truncated PDF417 contains only two row start columns. Some scanners and decoders cannot dependably read over 20 columns.

Truncated PDF417

A truncated PDF417 symbol uses less area than the normal PDF417 barcode. By selecting this option, the right hand side of the symbol is removed or truncated. This option should be used primarily in a clean environment, since it is more susceptible to damage.

The IDAutomation PDF417 Barcode Font and Encoder is a collection of encoders and components that generate PDF417 symbols as graphics or as a font. IDAutomation also offers new patent-pending Native Barcode Generators for JavaScript, Crystal Reports and Microsoft Access that create PDF417 without any plug-ins or fonts.

Barcode Integration Guides are also available that offer one or more integration options. These options may be examined to determine the best implementation method. A few of the guides offered include the following:

• Access
• Crystal Reports
• Excel
• Reporting Services
• C++
• C#
• VB 6 and Visual Basic .NET
• Web Barcodes

Barcode products generate images according to the pixels of the target device thereby creating an image difference. Consequently, it may be necessary to check the X or Y dimensions. Images and symbol sizes may differ slightly with various screen resolutions and printers.

To find the printed Y dimension, print a PDF417 barcode symbol with exactly 10 rows. To obtain 10 rows, choose 5 columns, an error correction of 2 and print the text of "IDAutomation.com, Inc. PDF417 ActiveX Control" with binary encoding. Measure the distance from the top of the symbol to the bottom and divide by 10. Example: if 10 rows measured .425 inches, then .425" divided by 10 equals .0425", giving a Y dimension of 42 mils per row.

To find the printed X dimension, measure 6 or more columns, but do not include the start and stop columns in the measurement, divide this number by the number of columns measured, then by 17. The result is the X dimension. Example: if 6 columns measure .875", divide .875” by 6, which equals .14583" per column. Because the X dimension width of each column is 17, take the .14583" and divide it by 17, which equals .00857", which is about 8 mils.

It is recommended to limit the amount of data in each 2D barcode symbol to 800 characters or less, using 20 columns or less. Although the specification states that "up to 1100 bytes or 1800 ASCII characters can be encoded in a PDF417 symbol," it is not usually achievable. The amount of data that can be encoded will vary depending upon the type of data, the compaction type, the error correction level chosen and the limitation of the scanner being used. For example, in text compaction mode, the amount of compaction varies due to mode switching between different types of characters, such as between numbers, upper case, lower case and punctuation. In addition, many PDF417 scanners do not reliably read more than 800 to 850 characters and some scanners have limits of only 300 characters. The IDAutomation USB Scanner with PDF417 dependably reads up to 500 characters. If it is necessary to encode more than 800 characters, IDAutomation recommends using Macro PDF mode or multiple separate symbols. In the best-case scenario, using the text encoding mode of the IDAutomation PDF417 Forms Control with the Hand Held Products 2D Barcode Imager, up to 1200 characters were successfully encoded and retrieved.

Each codeword represents 1 of 929 possible values, which allows data to be compacted into the codewords to save space. PDF417 has three data compaction modes: byte, text and numeric. Binary compaction encodes actual bytes of data; text mode encodes most characters on the U.S. keyboard. Numeric compaction encodes only numbers, is rarely used and not available in all products due to calculation limitations. The chart below shows more details about these modes.

To encode the most amount of data into the smallest possible symbol:

The amount of data compaction will vary depending upon the type of data that is being encoded and the error correction level chosen. If the scanner supports it, smaller symbols may be obtained by performing any of the following:

1. Use TEXT compaction mode.
2. Decrease the error correction level to 2.
3. Increase the number of columns to the largest possible size.
4. Decrease the X dimension to the smallest possible size the scanner will read.
5. Turn on truncation, which decreases the symbol size by two columns.
6. Choose an X to Y ratio of 1:3.

PDF417 allows ASCII functions to be easily encoded for various operations such as encoding tabs and returns. Normally, these characters are not visible unless an application is used such as IDAutomation's Barcode Scanner ASCII String Decoder, which displays these hidden functions as tags. In all IDAutomation products, the tilde (~) may be used to encode ASCII functions. For example; ~009 is used to encode a tab and ~013 encodes a return. In many development environments, Chr or Char may also be used to encode the ASCII value directly. For example, the programming examples below encode "PDF" <tab> 417:

Java: DataToEncode= "PDF" + (char)9 + "417";
Visual Basic: DataToEncode= "PDF" & Chr(9) & "417"

FedEx uses a combination of Code 128 and PDF417 barcodes on packing slips to automate delivery and tracking. FedEx publishes a FedEx Ground Multicode^SM Barcode Label Guide and a Barcode and Label Layout Specification Guide that should always be examined when implementing FedEx label applications.

The following is a summary of the PDF417 barcode requirements for FEDEX label printing:

1. The PDF Security Level or Error Correction Level must be set to 5.
2. The X dimension must be 10mils (.010" or .0254 CM) with an X to Y ratio (or N Dimension) of 5. To achieve this with the PDF417 Font and Encoder, print with the IDAutomationPDF417n5 font at 11 points.
3. The number of columns should be set to 10.
4. The entire message should not exceed 350 characters.
5. The quality of the symbol must be ANSI grade "A". The Hand Held Products 2D Barcode Imager's Print Quality Assessment may be used as a guide for this requirement.
6. The data encoded must begin with: [)>RS01GS where RS is ASCII 30 and GS is ASCII 29. In IDAutomation products, if ApplyTilde if set to "True" or "1," the format ~ddd is used to specify the ASCII code of the character to be encoded. These characters cannot be viewed or printed and therefore it may not appear to be present, unless an application is used such as IDAutomation's Barcode Scanner ASCII String Decoder.

NOTE: The code supplied below is an example and not a complete solution. More information about structuring messages to meet FedEx label specifications may be found at the FEDEX web site.

Java Example:
char GS = (char)29;
char RS = (char)30;
char EOT = (char)4;
rm.setData("[)>"+RS+ "01"+GS+ "9633626"+GS+ "840"+GS+ "002"+GS+"12345678901"+GS+"RPSC"+GS+"0988443"....

Visual Basic Example:
Dim NewMessage As String
Dim GS As String
Dim RS As String
Dim EOT As String
GS = Chr(29)
RS = Chr(30)
EOT = Chr(4)
NewMessage = "[)>" + RS + "01" + GS + "9633626" + GS + "840" + GS + "002" + GS + "12345678901" + GS + "RPSC" + GS + "0988443"...
PDF4171.DataToEncode = NewMessage

Tilde Processing of Control Characters

IDAutomation PDF417 barcode products all support the format ~ddd to specify the ASCII code of the character to be encoded, which allows easy encoding of GS, RS and EOT from the command line. 

For example, the following string:

"[)>"+RS+ "01"+GS+ "0133626"+GS+ "840"+GS+ "002"+GS...

May also be encoded with this string:

[)>~03001~02996336260000~029840~029002~029....

Before implementing the printed PDF417 barcodes for FedEx applications, it is recommended to verify the symbol with the Print Quality Assessment test of the Hand Held Products 2D Barcode Imager and Verifier or another suitable verifier. Additionally, the Metrologic Focus Scanner together with the Free Barcode Scanner ASCII String Decoder may be used to view the non-printable RS, GS and EOT lower ASCII functions, which will appear as tags. To perform the test, simply open the Barcode Scanner ASCII String Decoder and scan a MaxiCode symbol with the Image Reader.

It is possible to scan and encode international and extended characters, provided the instructions below are followed:

1. Encode the data using binary encoding. This option encodes all data, byte-by-byte.
2. Scan the data via the serial interface option (data bits have to be 8N) on the scanner. Normally, keyboard wedges and USB scanners do not support extended characters above ASCII 128, and only scan characters that are actually on the keyboard. Contact the scanner vendor for more information; some of the scanner's internal settings may have to be modified.

The most common method of reading  barcodes is with a PDF Capable Barcode Scanner such as the IDAutomation USB Scanner with PDF417 which reliably reads the IDAutomation PDF417 Font when printed as small as 3 points, which is an X-dimension of only 5 mils. Most of the hand-held barcode imagers recommended by IDAutomation perform keyboard emulation and receive power from the USB port, so that no external power supply is needed. When a barcode symbol is read using keyboard emulation, the data appears at the cursor as if it had been typed in from the keyboard.

In some cases, it may be desired to have the scanner trigger a form or action in an application. IDAutomation has documented easy methods of accomplishing this in the USB Barcode Scanner Application Integration Guide.

Printed symbols may be easily verified with the Print Quality Assessment test found in the Hand Held Products 2D Barcode Imager. The quality assurance test will grade the symbol and report the X dimension, Y dimension and any possible problems. The report below was generated when scanning the PDF symbol to the right with PQA enabled:

 >> PQA from Hand Held Products <<
PDF417: 10 rows x 3 cols, 22 data & 8 chks (ECL = 2)
X roughly = 0.009"
[A] < Row Height = 3.1 X
[A] < Useful Row Height = 2.4 X (76% Row)
[A] < Data Safety Margin = 100% (0 Erasures & 0 Errors)
[A] < Edge Accuracy = 72%
[A] < Print Growth = +1% of X

MacroPDF417 is an implementation of PDF417 capable of encoding very large amounts of data into multiple PDF417 barcodes. These multiple barcodes are then scanned by a MacroPDF enabled scanner, which reassembles them into one string of data. Each MacroPDF barcode segment shares a file ID with the other segments, which make up the entire barcode sequence. If the file ID is not the same, the scanner will assume that each of the segments belong to a different barcode sequence. In order for the scanner to reassemble the barcode in the correct order, each segment of the barcode must have a unique segment index, starting at zero. This unique segment index allows the scanner to know how to reassemble the barcode segments, and allows reading symbols in non-sequential order.

The latest 2D version of the following products generate MacroPDF417 symbols:

• .NET Windows Forms Controls - used to create and print barcodes from local .NET applications.
• ActiveX Barcode Control & DLL - this is the best product to use for Microsoft® Access reports and Visual Basic 6. It may also be used in C++.
• Barcode Image Generator - generates images one at a time or from the command prompt.
• Java Barcode Packages - these packages include JavaBeans, Servlets, Class Libraries & Applets that may be used on any operating system with a Java Virtual Machine including Linux, Unix and MAC.
• ASP Barcode Server Component for IIS - adds barcode streaming generation capability to Microsoft Internet Information Server.

The following scanner reads and assembles MacroPDF symbols:

• Symbol DS6608 2D Digital Scanner

Macro PDF417 Example

First Segment: MacroPDFEnable = True MacroPDFFileID = 237 MacroPDFSegmentIndex* = 0 MacroPDFLastSegment = False	Second Segment: MacroPDFEnable = True MacroPDFFileID = 237 MacroPDFSegmentIndex* = 1 MacroPDFLastSegment = True

Macro PDF417 Properties

• Macro PDF Enable - A boolean indicating that this barcode is part of a MacroPDF417 sequence.
• Macro PDF File ID - Assigns a file ID to the MacroPDF barcode. Each barcode in the MacroPDF sequence must have the same file ID assigned to it. Default is 0; valid options are 0-899.
• Macro PDF Segment Index - The index number of this MacroPDF barcode in relation to the set. Default is 0; valid options are 0-99998; * each barcode in the MacroPDF sequence must have a unique segment index, starting at zero and incrementing thereafter by 1.
• Macro PDF Last Segment - A boolean indicating that this is the final barcode in the MacroPDF sequence.

If assistance is needed, please contact IDAutomation.

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