How to preserve an archive of PCX files

A reader calling themselves “Specious” commented recently: “Another lost function from both Word and the OS is the ability to import PCX files. These used to be ubiquitous graphics files. Although little-used today, there are thousands of graphics PCS libraries – and, of course, many original archive documents were scanned and saved as PCX files.

“It would be very useful if the PCX graphics format could be re-integrated into Windows Explorer (from XP onwards) and also directly importable into Word documents. While there have been a few claimed kludges, with directions to import legacy graphics filters from, say, an old version of Microsoft Paint, nothing works as it did up to 2003. Perhaps there’s a challenge here for PC Pro and its readers.”

The PCX graphic file format was invented in the early 1980s when the world was using MS-DOS PCs with CGA and EGA graphics adapters. It predates even the VGA graphics adapter. CGA, the first colour graphics adapter for PCs, could show only 16 different colours, while Superior EGA graphics could show a palette of up to 16 colours from a total of 64.

As many modern software packages don’t support the PCX format, a legacy collection of PCX files is rapidly becoming a liability rather than an asset

Which colour number (0-15) mapped to what actual colour had to be set up in the colour palette chip on the display card, and the PCX file format stored this palette information in a fixed-length header at the beginning of each file. If you tried to show two different images that employed different palettes on the same screen at the same time, you were often left with one image looking okay while the other had garbled colours because it was being shown with the wrong palette.

Finally, the VGA card was invented – which displayed 256 colours out of a possible 262,144 – and PCX format couldn’t accommodate this enlarged palette, so it had to be amended to store its palette information at the end of the file, and by adding a flag bit in the header that said whether or not there was a VGA palette present. This was inefficient because the computer had to read the file header, discover that the image had its palette at the end, jump to read the last 768 bytes of the file to retrieve the palette information, then jump back to the beginning to start reading the actual image data. If you just read the file straight through, such an image would appear totally garbled since it had a spurious palette, then it would suddenly change to display correctly once the real palette had been loaded.

Specious remembers correctly that for many years PCX files were ubiquitous. They were used to distribute a lot of clip-art, many scanners outputted as PCX files, and even some fax applications employed them. However, their main use was in the MS-DOS application PC Paintbrush (made by ZSoft Corporation) for which they were originally designed. This was a simple painting and image manipulation tool that came bundled with many early mice, to give people a reason for purchasing one.

PC Paintbrush was later adapted to run under Windows and so survived for a remarkably long time, as did its file format. However, the file format is now so antiquated and graphics technology has moved on so far that it really is time to consider trading it in for something better. While it might technically be possible to write an Add-in for Microsoft Word that enables you to import PCX files, it would take a lot of effort and would solve the problem only for Word. There are lots of other applications out there that can’t use this archaic format, so it would be more sensible to ditch the PCX file format by bulk converting your file archive to a more modern format that has more widespread support.