This post is not what I thought it would end up being about. I had plans, but it seems fate, and the dark corners of my brain, had a different path set out for me. You see after I wrapped up my last post on PIC⁹³ I had LZSS compression on my mind, and thought maybe it was a good time to dive into LZSS. Specifically how it was used to compress the executable files for many MicroProse titles in the early 1990’s. I wasn’t even planning to blog about it at this time, it was only meant as a distraction for a little while. Then it happened…

Time to take on the last of the MicroProse PIC variants we have uncovered so far, PIC⁹³. This variant stands out from the others a bit as it is the first update to the format that we’ve seen in 3 years. Also to the best of our knowledge, the only released title ever to use it was Railroad Tycoon Deluxe (RRDX). RRDX is also one of the last titles to use the PIC format that we can see. Though even with that, the titles that did release after RRDX seem to have gone back to the PIC⁹⁰ variant. Another oddity is that this format seems, at first glance, closer in kin to the PIC⁸⁹ format than the PIC⁹⁰ format. PIC⁸⁹ being the format used with the games predecessor Railroad Tycoon. With that said, let’s dig into it and see if we can reveal its secrets.

In a previous post we investigated the remaining unknowns with the PIC⁹⁰ PIC⁸⁹ variant of the MicroProse PIC file format. This post will be more of the same, except this time we will tackle the PIC⁹¹ PIC⁹⁰ variant, bringing us one step closer to fully understanding the format, and it’s evolution, based on the sample set of files we have available to us. Also as a side note before we go on here, in that previous post I’ve updated it a bit to include the CGA remap/dithering rendering at the end to be complete.

Maybe not rewriting it, but correcting our recording of it. In my last post we analyzed the assets for a large number of titles from MicroProse that expanded our understanding of the sub variants and when they first came to use. As a result I am having to correct the designations I have been using to identify them.

We last left off having uncovered a dew more mysteries of the MicroProse PIC file format. We wrote a tool to examine PIC files to try and determine which version of the file they were, after some rework, we were fairly successful. Though in that process we uncovered a few new sub-variations in the data that we need to account for. In this post we will deal with those variations we discovered with the PIC⁹⁰ version.

Several posts back we looked at some other MicroProse titles and discovered that the PIC file format has evolved over the years with various titles. In this post we’re going to look at a few more titles that I found to have PIC files and see where they fit into the mix. Then we will hopefully be able to write some quick code to be able to identify what type of PIC file we’re looking at. This is a first stage to opening the newer variants up to our encoder/decoder.

We have some unfinished business to do in light of the discoveries we made last time. I now no longer trust my prior results with the RLE encoder, so we need to go back and revisit that result. Last post we wrapped things up by solving the red herring of the LZW compressor generating garbage. Which brings into question the issue we had surrounding the same file for RLE encoding. But first, we need to put all the pieces of the encoder together, and with that perhaps we can kill two birds with one stone. We can address the questionable RLE result, and we can fully validate our encode and decode stacks.