The backgrounds in Ninja Spirit never struck me as anything too special. To
my recollection, there are plenty of Turbo and PCE games with great
parallax scrolling. Anybody remember the backgrounds in Soldier Blade, Kaze
Kiri, Cotton, GoT, LoT, Parodius, Popful Mail, Genji Tsushin Agedama...
just to name a few off the top of my head. There's also some decent
parallax scrolling in the foregrounds of some of the fighting games like
SF2 CE, which by the way, look every bit as good as their SNES and Genesis
counterparts.
There are definitely games that look horrible as well such as Ys 3 and
Ninja Gaiden, but there seemed to be a turning point around 1991 or 1992
when somebody figured out how to do it right and plenty of games from that
point on had perfectly good parallax scrolling in them. Sadly, it seems the
vast majority of the U.S. releases were programmed before this revelation.
In the end, I don't think any fancy programming tricks or anything like
that had to be used. I'm sure programming parallax scrolling on the turbo
was eventually more or less the same as it was on SNES and Genesis and not
any more complicated. If you look at early Genesis games you'll also notice
a lack of parallax scrolling in a lot of titles. I can even recall a few
games on Genesis that had similar "bumpy background" problems. I was just
playing an old Mega Drive shooter the other day called "Curse" (I'm not
sure if it was released in the U.S.). That game looks really bumpy. Also,
the Genesis version of Ys 3 often times used a stationary background that
stayed in one position while the foreground moved in front of it rather
than true parallax, though it looked a lot better than the turbo one of
course.
I think the primary factor is the age of the game and the programming
techniques used at that time. Good looking parallax scrolling didn't become
that common until some time in the early 90's.
~Kaze
Turbo Turnpike
http://j-fan.com/turbo/