I just noticed there were replies to my comment. I did a quick search and found this: http://atarihq.com/danb/IRobot/Video%20hardware%20info.txt http://atarihq

I just noticed there were replies to my comment. I did a quick search and found this: http://atarihq.com/danb/IRobot/Video%20hardware%20info.txt http://atarihq.com/danb/IRobot/Video%20hardware%20info.txt It has a bit more detail about the pixel format. Unlike what I said, it was 6b color index and one bit for video timing (what I was calling 1/2 pixel stretch). In essence it conveys whether the right edge of a given scanline is best represented by a transition in the middle of a pixel. That works great for most cases, but would not work well when edges from two different triangles intersection (if they weren't actually sharing the exact same edge, if you know what I mean). This site has schemtics: http://www.ionpool.net/arcade/irobot/manuals.html http://www.ionpool.net/arcade/irobot/manuals.html Page 17 shows the 7th bit, called "RAWHALF", which gets buffered to become "PXSPLIT", and that signal is used to fiddle the clock which is sampling the raw pixel index. I didn't dig enough to know exactly what this means, but that is the place to look.