PDF417 is capable of encoding all 256 values (bytes). Except the NUL character, which serves as the terminator for C language, you can enter all these characters as is. However, in some situations you may want to use the escape method, because your environment does not support entering control characters, or you are entering symbology specific features. For example:

The escape method described here is called tilde method. When creating PDF417 barcodes you can use the following tilde codes:

For more information on entering ECI and Macro PDF417 block, see Appendix A, Input Format for ECI and Macro PDF417.

PDF417 allows users selection of security level. While the default algorithm^[2] is appropriate to most applications, you may want to increase the amount of error correction. Higher error correction level increases the size of the barcode, but is more resistant to various errors, such as printing error and symbol damage during the transport.

Internally, each symbol uses one of eight levels of error correction. Increasing the error correction by one level doubles the number of error correction codewords. In turn, it roughly doubles the amount of damage that the symbol can tolerate.

In our software, you can specify 9 to indicate that you want to use the default algorithm.

Since a PDF417 symbol must be rectangular, when the total number of data and security codewords does not make up a rectangle, padding codewords are added to fill the spaces. The padding codewords just fill the space, and do not increase the error resistance of the symbol^[3] For this reason, our software consider the security level you requested as minimum, not the exact requirement. That is, if the symbol size required can't satisfy the security level requirement, the software reports an error. However, if the security level can be increased within the size specified, it selects a higher security level. The principle here is to reduce the number of useless padding codewords and increase the ECC codewords without increasing the overall symbol size. This arrangement makes the symbols produced more robust.

Apsect Ratio does not affect the decision when you specify both the number of rows and columns. when you only specify one of them, or not at all, it kicks in. The aspect ratio of a symbol is the ratio of its overall height vs. its width. For example, if your aesthetics suggest that the symbol looks better when the width is approximately 3 times its height, the aspect ratio is 0.33.

The value of aspect ratio is considered recommended unlike other parameters. Other parameters entered are either considered minimum (such as security level) or exact (such as number of rows). It is not possible to achieve the exact value. It enables the encoder to compare all possible row and column combinations and select one that produces the closest match.

In order for the encoder to calculate the aspect ratio of the symbol, the encoder has to know another parameter, yHeight, which is the height of a module vs. its width. Because this parameter only affects Aspect Ratio, it impacts only when Aspect Ratio is considered during the selection process. If you specify both rows and columns, or aspect ratio is 0, it does not have any effect.

The yHeight is the height of the module vs. it width. For better decodability, yHeight should be greater than 3.0. After number of rows and columns are determined, yHeight affects the final symbol size.

If you are using font-based approach, note that yHeight is fixed per font. For example, MRV PDF417N3 has a fixed yHeight of 3.1.

The module width is the width of the module. It is an important parameter that affect overall symbol quality. We will explain its selection in the next section.

Compact PDF417 was referred as Truncated PDF417 in previous standard. Compact PDF417 may be used where space is a primary concern and the symbol damage is unlikely, such as in an office environment. It removes the right row indicator, and reduces the stop pattern into a single bar.

Figure 2.2. Example Compact PDF417 symbol

Creating barcodes using fonts involves two distinct processes: encoding and rendering. Rendering is to choose the appropriate font and font size and format the encoding results. Encoding is to convert the data into a special string, a.k.a. Barcode String, which becomes a barcode after being formatted with an appropriate font.

The Font-based approach is easy to understand, and in some occasions the only way to add barcode printing functionality, such as in Crystal Reports.

The drawing below illustrates how you create a PDF417 symbol using font-based approach. You first create the barcode string (which is an array of text lines). Format the barcode string with MRV PDF417 N3 font you get the barcode.

You can export barcodes as standard image files to be consumed in other word processing and imaging programs. The PDF417 Encoder GUI supports exporting images in five formats via a GUI interface. The Encoder DLL and PDF417 ActiveX Control also provides programming interfaces to export images in those formats:

Special attention should be paid when the target printer has low resolution, such as a thermal printer or fax machine. When generating vector graphics files, the software allows you to specify target dpi which you should set to the one that matches your printer. It is generally not recommended to scale the image down or up when working with low-resolution printers.

PDF417 Font Encoder DLL provides a method to retrieve a Windows enhanced metafile (EMF) handle that can be used to print to printers. The PDF417 ActiveX control provides a similar feature through its Picture property.

For environments that support ActiveX Controls (also called OLE controls), you can insert the PDF417 ActiveX Control into documents, spreadsheets, or invokes the control at the background in your program. With ActiveX Control you are able to change the barcode image by editing its properties.

Using ActiveX Control in Microsoft Office programs is straightforward. Programming knowledge is required in order to integrate the control with your custom programs.