Last year I was contacted by Brian Bagnall, the author of "On the Edge: The Spectacular Rise and Fall of Commodore" about the founding of MicroGraphicImage.  The following is the synopsis I sent him.

MicroGraphicImage was started by former employees of a company called "Games By Apollo".  It had been among the companies that had pumped out fairly crummy games for the Atari 2600.  Companies like GPA, overproduced games creating a glut of cheap games.  In the pre-Christmas market of 1982 the company became filed for Chapter 11 Bankruptcy.  Unfortunately, they had a lot of really good games in the works for a number of platforms, including the Atari 800/400.  I had been one of the lead developers on the 800 platform and Tim Martin had been on the Atari 2600.
 
When GPA went broke, Tim Martin and another ex-GPA 2600 developer, Robert Barber, developed a game entitled "Halloween" based on the infamous movie.  The contract funded the founding of MicroGraphicImage(MGI).  Unfortunately, the company holding the rights to Halloween went bankrupt in the video game depression of 1982-83.  This was a shame because the game was really very good considering the restrictions of the the Atari 2600 and was ahead of its time in content and usage of the Halloween theme music.
 
Tim and Robert's expertise was with the Atari 2600.  Furthermore they were dis-satisfied with kind of money being made through contract game development.  Their strategy was to utilize the contract programming to leverage the funding of a Software Publishing company.  The brought me in as technical specialist with Atari and Apple computer programming.  We went to the January '83 CES in Las Vegas.  It was there we developed a relationship with Gary Carlson, one of the founding brothers of Broderbund.  BTW, Gary and Broderbund were the class act in an industry of quick con artists.
 
In early 1983 MGI developed games under contract for Broderbund, Parker Brothers, and CBS Electronics while developing Spelunker for ourselves.  Tim and Robert had been developing the game design for quite a while.  However, it was too ambitious for the Atari 2600.  Tim, Robert and myself co-developed the game.  Tim was responsible for "game logic", I developed the graphic engine and Game Level Editor, and Robert was the graphic designer and Level Editor.
 
Technically, it used the Atari Graphics Mode 4.  GM4 provided for 4+1 color characters.  This means a color character had 4 colors with a 5th alternate based on the high bit of the character.  The "Spelunker Dude", Bats, Ghosts and flares were done using Sprites.  Because two sprites were dedicated to the Dude, it left 2 sprites for the rest.  It took two sprites to make a 3 color image.  This is what we used for the Dude.  The remaining sprites made single color images.  The massive amount of screen movement (relative to the day) was done by animating the GM4 characters.  Sequencing changes to the character definitions provided for the instantaneous movement where ever the characters appeared on the screen.  Elevators, moving earth, and animated treasures were accomplished using this technique. The 5th color was the "deadly pink" that was so lethal to the Dude.  We used hardware sprite collision detection to trigger the quick death that would occur whenever contact was made.  The Atari 800 had a programmable graphics chip we exploited for the smooth scrolling of the large cavern.  This was critical for giving the sense of the "huge unknown".  Most games at the time flipped screens whenever a character ran off the side.
 
Robert Barber was a really talented game designer and was responsible for the Cavern layout and the look and feel of the graphics.  One of the things that added to the strength of Spelunker was the team development.  1983, most games were designed and developed by a single guy.  This explains why the graphics was frequently poor.  The guy who was great at writing extraordinary bit-twiddling wasn't necessarily a good artists.  The good artist wasn't necessarily a great game visionary.  With Spelunker, I was the bit-twiddler.  Tim and Robert were the game visionaries.  Today, it's not unusual to see a couple hundred contributors on a game. 

In 1983, all computer games had a "name" attached to it.  It was sort of a "rock star" mentality. Spelunker was Tim's original idea and programmed the game logic. When the game was released, we made a strategic decision to put Tim name out front.  Besides, we were all convinced this was the first of many games and we would all have our turn.  Unfortunately, the game recession that started in the winter of 82, only got worse.  It was very difficult to get game distributors to take games from small single game publishers.  Even though we were able to maintain a steady stream of contract work, the overhead of financial business focus going into publishing, we weren't able to make ends meet.
 
In 1984, we turned publication over to Broderbund and made the Commodore 64 version.  The C64 was very similar to the Atari.  In fact, very little had to be changed.  It had a Character Graphic mode compatible with the Atari GM1.  It had better Sprite and sound support but we didn't do much to exploit this.  It was primarily a "port".
 
At MGI, we loved the Atari and really didn't care much for the C64.  We always found it to be a bit ironic that the Atari had a reputation as a "Game Machine" and the C64 was a more serious computer.  From our perspective, the C64 had an edge when it came to sprites and sound.  However the Disk OS was really bad.  It couldn't even boot from a floppy!  Not only did the Atari have a much better Disk, but the OS was much more well rounded with multi-device support.  In short, the C64 was a better game machine and the Atari was a more serious computer!
 
Eventually, MGI ran out of money and closed its doors.  In didn't really go bankrupt, it simply stopped operation.  Tim continued working with Broderbund on a business level and was able recover all debt through the NES and Coin-op versions.
 
Tim and I continued to work together including an Amiga Publishing company by the name of Inovatronics.  Eventually, Tim was a founder of the Internet Provider, Internet America.  I'm still a bit twiddler and currently work at Perot Systems.