I noticed that someone on the clickteam forums had created a Scale2x shader (the kind of thing used in various emulators to smoothly enlarge pixel art), but had not released it to the public - and so I set about creating my own.
Although it was supposed to be a direct copy of the Scale2x algorithm, there's some unintentional color bleeding, which gives a nice anti-aliased look
Actually, I tend to agree with you on that - at least when it comes to true pixel art. You always feel like you lose some of the sharpness and detail when using these filters.
Where I think they are really great though, is for emulation of modern handheld consoles (eg. GameboyAdvance), which use low-resolution but high-color graphics. In this case, the graphics often aren't true pixel art - rather, they're pre-rendered 3d graphics or whatever ("Golden Sun" is one example), that have been scaled down. Consequently, there isn't really any detail there to be lost, and filters usually make the graphics look much better.
This is exactly what I am looing for, but how do you use it correctly? Is there any example file? Also is it possible to set this effect to a layer to get the effect on the whole game, or do it have to be on individual objects?