artifacting colors

[andylama]

Some games, notably the Ultima series, took advantage of the graphic artifacting to create colors in the otherwise monochrome games.

 

When playing Ultima on an Atari 800, you get green trees/grass and blue water; it looks appropriate. This same screen on an XL machine shows up as blue trees and red water--bizarre.

 

Is there any way to 'correct' the artifact colors on an XL machine (and I don't mean the TINT control on the TV set), or is this a hard-coded feature of the chipset? I'm not afraid to take a soldering iron to the motherboard...

 

Thanks

[Goochman]

I think it can be altered by software - running the translator may change the behavior but I cant remember for sure.

 

There were some games that asked if you had an XL or not and adjusted accordingly.

[Bryan]

Is there any way to 'correct' the artifact colors on an XL machine (and I don't mean the TINT control on the TV set), or is this a hard-coded feature of the chipset?  I'm not afraid to take a soldering iron to the motherboard...

 

Sorry, it cannot be easily changed. It has to do with the alignment of the Chroma and Luma signals in each machine. Since the video output circuits are different in the 800 and XL, there is a slight phase difference between the two, and that changes the artifacts that are produced.

 

-Bry

 

Remember that "artifacting" means to produce a false chroma signal using alternating luminances. Therefore, the produced color signal has the phase of the luma signal, not the chroma signal. The colorburst reference phase is still generated by the chroma signal, so the difference in phase between the chroma and luma signals determines the artifact colors.

[VW]

I know that for Ultima at least, there was a way when you first boot up to tell it which color mode to use, I'd have to check my reference card to be sure but I know there is a way, I'll post when I look it up.