PMDF System Manager's Guide

Almost all inbound FAX processing is done by the DATA_TO_BITMAP channel. It is the job of this channel to convert the raw data stream read from the FAX modem into a more palatable image format (e.g., DDIF) and then send this processed FAX on to either a designated e-mail address, a spooled printer queue, or a file on disk. Only one of these "dispositions" may be used for a given DATA_TO_BITMAP channel.

Only one image format may be used for a given DATA_TO_BITMAP channel. The supported image formats are

DDIF

The Compound Document Architecture (CDA) DDIF format is supported. All of the pages of single FAX are stored in one DDIF file with a filename extension of .DDIF; each page is stored as a separate, Group 4 compressed image in that file. This format is recognized by VMS MAIL, PMDF MAIL, DECwindows MAIL, and MailWorks (A1MAIL) and accepted preferentially by most Compaq supplied, image-capable software. DDIF files may be converted to other formats using the OpenVMS CONVERT/DOCUMENT command; e.g.,

$ CONVERT/DOCUMENT fax.diff/FORMAT=DDIF fax.ps/FORMAT=PS

and viewed with the CDA VIEWER

$ VIEW/INTERFACE=DECWINDOWS fax.diff

GIF

Both version 87a and 89a of the Graphics Interchange Format (GIF) are supported. All of the pages of a single FAX are stored in a single GIF file with a filename extension of .gif; each page is stored as a separate, compressed image in that file. GIF 89a should be used when possible as it supports the concept of non-square pixels (i.e., pixels for which the aspect ratio --- the ratio of height to width --- is not 1:1). Most FAXes are sent at low resolution and the pixels have an aspect ratio of 2:1. The GIF image format is supported by many popular UNIX mail readers. However, be warned that some GIF image viewing software will only display the first image stored in a GIF file and therefore may only display the first page of a FAX. This limitation is usually stated in the "known bugs" section of the documentation for the viewer software.

LN03 sixel

The LN03 sixel image format should be used when producing output for an LN03 laser printer or other sixel device with a resolution of 300 dpi. All of the pages of a single FAX are stored in a single file with a filename extension of .sixel; depending upon the length of each FAX page, one or more pages of LN03 output will be generated.

PCL

Versions 3, 4, and 5 of Hewlett Packard's Printer Control Language (PCL) are supported. PCL 3 is typically used by LaserJet, LaserJet Plus, and LaserJet II printers, PCL 4 by the LaserJet II series printers other than the original LaserJet II itself (e.g., LaserJet IIp, LaserJet IId), and PCL 5 by LaserJet III series printers. Both mode 2 and 3 compression are supported: mode 3 will be used for printers supporting PCL 5 and mode 2 by printers supporting PCL 4. The PCL image format should be used whenever possible with 300 dpi LaserJet or LaserJet compatible printers. Avoid using PostScript if at all possible as PCL image (raster) files are much more compact than their PostScript counterparts. All of the pages of a single FAX are stored in a single file with a filename extension of .pcl; depending upon the settings of the DATA_TO_BITMAP PAGE_ channel options, one or more pages of PCL output will be generated for each FAX page.

PostScript

Adobe's PostScript Levels 1 and 2 are supported. The PostScript file output is not an encapsulated PostScript (EPS) file but does conform to the level 2 Document Structuring Conventions. Use Postscript Level 1 when spooling received FAXes to a printer with a PostScript Level 1 interpreter; use PostScript Level 2 when spooling to a printer with a PostScript Level 2 interpreter. Be warned that FAXes stored using PostScript Level 1 are quite large and typically take up 910 (standard resolution) or 1850 (fine resolution) blocks per FAX page. Printing such large files can be very time consuming when using a serial line to communicate with the printer (7 or 14 minutes per page). FAXes stored using PostScript Level 2 are quite compact and print fairly quickly. With PostScript Level 2, each FAX page is compressed using the CCITT two-dimensional Group 4 FAX compression scheme. All of the pages of a single FAX are stored in a single file with a filename extension of .ps; depending upon the settings of the DATA_TO_BITMAP PAGE_ channel options, one or more pages of PostScript output will be generated for each FAX page. By setting the PAGE_MAGNIFICATION option to -1, each FAX page will, if longer than the length of the page, be vertically rescaled so as to print entirely on a single page.

TIFF

Version 5.0 of Aldus's Tagged Image File Format (TIFF) is supported. All of the pages of a FAX are stored in a single TIFF file with a filename extension of .tiff; each FAX page is stored as a Group 4 compressed, Class F image in that file. The TIFF image format is supported by many popular UNIX mail readers.

The choice of image format will be dictated by the the choice of disposition. For instance, received FAXes delivered as e-mail to a VMS MAIL or A1MAIL mailbox are best sent in the DDIF image format since the DECwindows and Motif user agents for VMS MAIL and A1MAIL are capable of (automatically) displaying such images. Moreover, these user agents can forward DDIF images to other mail users and extract them to files (e.g., for subsequent printing). If received FAXes are to be delivered as e-mail to a UNIX system and read with a MIME-compliant user agent, then TIFF or GIF would be a good choice.⁹ When spooling FAXes to a printer, the choice of image format will be dictated by the type of printer.