Also Known As: FAX, Facsimile File Formats
|Compression||RLE, CCITT Group 3, CCITT Group 4|
|Maximum Image Size||1728x2200 pixels (typical)|
|Multiple Images Per File||No|
|Supporting Applications||Too numerous to list|
|See Also||TIFF, PCX, Chapter 9, Data Compression|
Storage of FAX images received through computer-based FAX and FAX-modem boards.
There is no one single FAX format. The closest to standard are the formats based on a proprietary specification, such as PCX or TIFF. Consider yourself blessed if the format you need to support is one of these.
Code fragments are available for this format.
Sample images are available for this format.
There are many facsimile (FAX) file formats, almost as many as there are FAX add-in boards. The PC-based HiJaak Graphics File Conversion Utility (by Inset Systems), as of version 2.1, supports no fewer than 22 different FAX file formats. Each format, however, is basically the same, and consists of a binary header, followed by one or more sections of compressed image data. The data encoding is usually a variant of RLE, CCITT Group 3 or CCITT Group 4. Several FAX formats, in fact, are proprietary variants of better-known formats, such as TIFF and PCX.
For Further Information
Even though all of these FAX file formats were created to store the same kind of image data obtained from the same type of hardware device (i.e., FAX cards), each one is slightly different from all the others. This is problematic.
The evolution of the FAX card industry in some ways recapitulates the early evolution of the computer industry as a whole. Each company perhaps imagined it was working alone, or, if not, would quickly come to dominate the market. As the presence of competition became clear, a mad scramble to ship products ensued, and corners were cut. Because companies making FAX cards are by definition hardware-oriented, you can guess where the corners were cut: software.
As the industry started to mature, companies realized that competition was a fact of life, and tried to differentiate their products. One way to do so was through the promulgation of proprietary "standards," designed to keep the originator company one jump ahead of any competition unlucky enough not to be able to push their own specification. Add an unhealthy glop of NIH ("not invented here") spread liberally over the entire FAX board industry, and you have the present situation.
Recently, there have been signs of true maturity in the FAX card industry, with the emergence of the realization that all companies benefit by standardization, and an effort in this direction has been underway for some time. An extension of the TIFF file format, called TIFF Class F, would add the necessary tag extensions to allow easier storage and manipulation of FAX images stored in TIFF format files. (For further information, see the article on TIFF.) At the time of this writing, only one company, Everex, has adopted the unofficial TIFF Class F as its FAX file format standard (perhaps because a now-dead subsidiary of Everex, Cygnet Technologies, pioneered TIFF Class F).
If you need to need to convert FAX file formats, you will need a very versatile conversion utility, such as HiJaak. If you need to write code for an application that reads and writes one or more FAX file formats, you will ordinarily need to contact the manufacturer of the FAX card and obtain any information they are willing to release. If your FAX format is a common one and worth supporting, you should find that you are able to obtain the specifications you need from the manufacturer.
As mentioned above, the best source of information on FAX file formats is from the manufacturer of the FAX card you wish to support. Some FAX card companies publish developers' toolkits for designing software to work with their FAX cards. Unless a company considers its format proprietary, it will have some sort of specification available for their FAX file format.
For more information about TIFF Class F, see the TIFF article. You may also be able to obtain the following document:
Campbell, Joe. The Spirit of TIFF Class F, Cygnet Technologies, Berkeley, CA, April 1990.
Cygnet is no longer in business, and Aldus took over support of the TIFF Class F specification. Aldus has recently merged with Adobe Systems, which now holds the copyright to the TIFF specification and administers and maintains the TIFF format.
All information on the TIFF format may now be obtained through the Adobe Developer Support group. However, this group supplies only general TIFF information and does not provide any TIFF tutoring, sample TIFF source code, or sample TIFF files. Contact the Adobe Developer Support group, at [email protected]
Questions about the the Adobe Developer's Association should be directed to:
Adobe Developer's Association
1585 Charleston Road
P.O. Box 7900
Mountain View CA 94039-7900
This page is taken from the Encyclopedia of Graphics File Formats and is licensed by O'Reilly under the Creative Common/Attribution license.