I took a trip to Africa in 1995, and over the course of about 10 days I shot some 15 rolls of 36-exposure slide film. This was in the early days of digital imaging, particularly for consumer cameras, so I was still using film, but I wanted to get the best of those pictures in digital format as well. I chose 100 of the best ones, and had the local camera shop send them to Kodak to be put on a PhotoCD. This was not the "Picture CD" which later became very popular; PhotoCD was a proprietary format which was developed by Kodak for storing digital images. I could write for quite a while about the pros and cons of the PhotoCD format, but the important thing about for me at this time is that it was popular in 1995, but by 2000 or so it had been pretty much replaced by JPEG format images. Fortunately for me, the software to read and display the .pcd files was included on the PhotoCD itself; unfortunately for me, it was Windows-only softare, and it didn't actually do all that much beyond displaying the pictures.
The result of all of this was that for the past 5-10 years I have seldom, if ever, looked at the pictures on that PhotoCD. Getting the new Kodak Photo Scanner last week, and starting to scan all of those Africa slides, got me thinking about the PhotoCD again, and wondering if I could convert those .pcd files into something more common that I could display on my Linux systems, use as wallpaper, screensaver, and so on. I did some research on the web, and found some very interesting information about the pros and cons of the PCD format, but not a lot about actually reading and converting the images. I found one or two commercial programs, for both Windows and Linux, which could read and convert them, but there always seemed to be a lot of discussion about variable quality in the converted images. Then I saw something that said ImageMagick did a pretty good job of it.
Wow, could this be the ImageMagick which I knew from years ago as a set of command-line tools for image conversion and manipulation? Indeed it was, and then I got even better news - I found that it is included in the base installation of Linux Mint! So the tool that I needed had been right in front of my nose the whole time! A little bit of reading of the man page, web page and documentation, and I was able to convert a .pcd file to JPEG, and get whichever of the six resolutions I wanted. Hooray! Of course, because this is a command line tool, I could then easily run it in a loop and convert all of the images... or extend the loop and extract several resolutions of all of the images... this is just great!
If you are interested in the details of the rise and fall of the pcd file format, the Wikipdeia article is a good start. On the other hand if you have pcd pictures and want to convert them, check your Linux system for ImageMagick, if it's not installed it will almost certainly be available in a repository. If you can't find it anywhere else, check the ImageMagick web page for sources and binaries - yes, it's FOSS!