INFO: Group 3 fax image format.

ZTN1004

ID: ZTN1004

This Zetafax technical note applies to:

• Zetafax 5 client and later

Summary

Zetafax uses the TIFF file format for storing faxes.  TIFF is a very flexible standard for storing graphics files, and this document details the specific format of TIFF which is used.

The Zetafax client allows you to submit many other graphics file formats for sending, and will convert them into TIFF files for submission to the server or saving as attachment files etc.

From version 6 of the Zetafax API (when used with a Zetafax 6 or later server), the Zetafax server will also convert submitted graphics files into the correct format.  However, it is more efficient to supply a file in the "native" TIFF format if this is available.

Version 5.5 or earlier of the Zetafax server and API did not support format conversion - any graphics files supplied must be in precisely the correct TIFF format.

More information

Zetafax native TIFF files have the following main capabilities:

• 1728 pixels per scan line - see note below
• Resolution of 204 x 196 dpi or 204 x 98 dpi - "200 x 200" and "200 x 100" are also supported for compability with earlier systems
• 1 dimensional encoding (otherwise known as Modified Huffman or MH)
• 1 data strip per page

The Zetafax server is not a generic TIFF reader - while it will attempt to read files with these settings not all combinations of other tag values will be supported.

Zetafax uses the extensions .G3F and .G3N for fine and normal resolution TIFF files respectively.  If you are generating a TIFF file which is not being treated correctly by Zetafax, we recommend you analyse one of the example Zetafax files (eg "BAR-B-Q.G3F") to check and copy the format exactly.  Alternatively, if using Zetafax 6.01 or later, try supplying the file in a different format (eg different data compression encoding) and let Zetafax convert the format using its general purpose graphics filters.

Note that Zetafax 6.00f and earlier did not check the scan line width, and assumed the width was 1728 for MH encoded TIFF files.  This gave incorrect results if a file of a different width was supplied - the Zetafax viewer did not display it correctly if you moved to the bottom of the displayed page then returned to the top, and if sent using certain fax devices the fax image could be corrupted.  From Zetafax 6.01 a file with the wrong width will be converted as with other incompatible formats.

Last updated: 4 January 2000 (GC/GW)

Last verified 10/10/2005 (EB)