Compile all the *.java files. (If you're using a 1.0 Java VM, you can use the supplied naplps.zip classes file). Set your CLASSPATH if necessary. Run the Viewer ("java naplps.Viewer"). Use the "File"->"Open" menu and dialog to open a NAPLPS PDI file (.nap or .pdi, some sample .pdi files are included.) Have fun.
NAPLPS is the North American Presentation Level Syntax Protocol, ANSI X3.110. This code goes back to the mid-1980s, originally intended as a flexible protocol for displaying text & graphic pages on computers via phone lines. (Think of it as an early version of the Web.) It's optimized for low speed links and relatively low-res screens.
However, it has some advantages over the common bitmap images (.gif, .jpg, .png etc) in that it's a vector- or object-based format rather than raster (although it can include raster images). This means the drawing sequence can be replayed and edited, which could be useful for e.g. conferencing/collaboration systems. (The conferencing system CoSy that I wrote at U Guelph supported the embedding of NAPLPS images in messages, but there was never any client software to take advantage of that capability.)
NAPLPS can include timing instructions (WAIT), providing an animation capability by successively drawing slightly different images in the same area between waits.
See also this link for additional notes and references.
As part of a reimplementation of CoSy, in Java, that I started a couple of years ago, I wanted to include appropriate client software to support graphics as well as text. That client software (which can act as a distributed whiteboard) is on my home page under "JCoSy", but it uses this naplps package for decoding the PDI's (picture description instructions).
What is here is the naplps decoder package, which includes a viewer to look at sample NAPLPS files (*.nap and *.pdi). NAPLPS, despite its name (North American etc) seems to have caught on in Japan as a file format, some of the sample files here were borrowed from Japanese web sites (there's even a Netscape plugin available out there somewhere for NAPLPS).
The basic graphic stuff works, meaning that a displayed file will generally look more-or-less like it's supposed to.
However, there's lots of work left. Specifically:
This was originally developed using JDK 1.0.2-5, so there are some methods that are deprecated in 1.1, and perhaps more so in 1.2. It compiles (with warnings) under JDK 1.1.7, and seems to run alright.
The classes in naplps.zip were compiled with JDK 1.0.5, you might need to recompile if you're using 1.1 or 1.2. (Late news: they run fine using a 1.1 JVM without recompiling.)
This code is released under the GPL. See the file "Copying" for details. Basically you can do what you like with it, but if you distribute anything based on it, you have to provide the source, you can only charge reasonable distribution (not licensing) fees, and release under a GPL-compatible license.
Cheers.