[an error occurred while processing this directive]


jargon busters mainJargon Busters -
Try conversion - (July 1999)
David Angwin takes us through converting documents from native file format to fax image format.

[an error occurred while processing this directive]

When electronic documents are faxed via a network fax server, the document that is received on the destination fax machine should look the same as the original document. While most fax servers provide a "What You See is What You Get" or a "What You Print is What You Get" feature, in reality some products are more successful in delivering on this promise than others. This is because the method of document conversion used by different fax server products varies greatly. The way in which a fax server product converts documents from native format to fax image format has an impact in the following areas:

  • Quality of Reproduction: The appearance of the fax image and its faithfulness to the original document.
  • Scope of document formats handled: How many different document formats can the fax server application handle and convert successfully to a fax image?
  • Throughput: How does the fax server’s document conversion process impact the performance of the server to send and receive faxes?

Before a fax server can send a document, it must convert it from its native format to a standard bitmap image format – Group 3 TIFF format. Either the document is converted by the client desktop computer and then sent to the fax server, or sent to the fax server in its native format and then converted to an image at that point. Documents can be converted on the client desktop when software to do this conversion has been installed on the desktop. There are various options to initiate this client-based document conversion:

  • "Print-to-Fax" within any desktop application.
  • "Print-to-Fax" within any desktop application, using a Web Browser.
  • "Print-to-Mail" within any desktop application.

In all cases, when the fax client, e-mail client, or Web browser pops up, the document has already been converted on the client from its native file format to a faxable image format.

Conversion approaches

There are two approaches that are commonly taken for converting documents on the client desktop. In either method, the end-goal is to convert the document into the TIFF format that is used by most fax modems and fax boards. Many fax servers convert the document to an intermediate format – a PCL image – and then let the fax server finish the conversion to a TIFF image. Most fax servers have selected this method because it is easy to create a PCL conversion driver to be used within desktop applications. PCL converters are a slight variant of the standard print drivers provided by Microsoft. The problem with this two-step conversion is that it creates a performance bottleneck on the fax server because it must now convert all its documents from PCL to TIFF before sending them out.

For small LAN fax servers with a handful of telephone lines, the bottleneck caused may not be significant. However, in a high volume enterprise server it may be critical to not have the fax server responsible for this extra step. A one-step conversion model, as used by Omtool’s Fax Sr., avoids the need for this extra step and as a result, reduces the processing load on the fax server.

Fax servers should support both these methods of document conversion, as there are times when it is important that the faxed document appears exactly as it would appear on a printer – What You Print is What You Get. Certain printer specific formatting can take place while converting a document from its native format to a PCL or Postscript image. Converting the document directly to a TIFF image would not take into account any printer-specific formatting commands.


There are many cases in which converting the document to a faxable image on the client is either not desirable or not possible at all:

  • The user sends a fax and specifies that the fax should consist of multiple attached documents. Since each of the documents was simply attached to a message, there is no opportunity to run the documents through the print to image converter on the client.
  • To minimise the number of software applications being supported, corporate standards may prohibit fax client software from being installed on each user’s PC.
  • When faxes are submitted to the fax server from other back-office business applications using the fax server’s API. In this case no client is involved in the definition and creating of the fax, so converting the document to an image on the client is not possible.

Fax servers should provide a comprehensive approach to document processing on the server to give the system manager a choice of conversion via third party software or by OLE or DDE communication with the application software.

Third party software

Third party document conversion software is a popular option but can have limitations. The conversion filters may not handle every commonly used document type; they might not convert the document as perfectly as the application that created the document; and the version of the desktop application that they support may trail the latest release of the desktop application. However, they are simple to configure and usually produce acceptable results. If the quality of the third party conversion for a specific desktop application format is not satisfactory, the fax server’s OLE or DDE interface to the original application can be used to convert the document to an image. The OLE interface is easily expandable, and has been created for the most popular software, including the three most popular office suites.

If the application cannot be communicated with via OLE, you can still use the fax server’s DDE interface to instruct the application to generate a print image that can be faxed. Connection using an OLE or DDE interface will consistently give accurate document conversion.

In conclusion, the most important features of the document conversion system employed by a fax server product are the ability to:

  • produce a quality fax image
  • handle all possible formats of documents
  • optimise system resources so as to eliminate processing bottlenecks
    jargon busters main

[an error occurred while processing this directive]