This algorithm doesn't seem to do a good job of handling anti-aliasing or dithering, which I would have expected to be listed among their style-preserving properties. Their R vs Я example is a very good illustration of why that's difficult, as it could also be interpreted as a small dithered gradient.
Another thing I have been wondering for a while is that, as far as I know, these algorithms work on the final picture, after all the backgrounds and sprites have been drawn. I wonder if scaling every layer independently and then compositing them would give better results.
> MMPX is sufficiently fast and high enough quality for run-time application in retro game/hardware emulators. Yet, we offer two cautions about using any filter in this manner. [...] true retro hardware and content was designed for cathode ray tube displays. [...] Artists created content with these characteristics in mind and often exploited them. [...] Display-independent magnification algorithms will not properly take frequency content and display filtering into account. They produce net results that may be attractive and useful, but one must acknowledge that the perceived image is not faithful to the original artistic intent.
Growing up as a PC gamer using VGA, I never experienced that kind of blurriness, and in fact I though that consoles over composite video looked awful.