I had to improve the scaling quality in our current product (actually in the 2d presentation module), so I tested some filtering techniques. After building some releases with exotic algorithms (Blackman, Hamming), the feedback received and our observations led us to the conclusion that the simple bilinear filtering has the best visual effect.

It will support OpenGL rendering, using maximum (16X) anisotropic filtering for best quality available (with mipmaps of course) (should switch to software rendering for machines with on-board video and strong CPU).

The image edges will be anti-aliased using alpha channel and bilinear filtering (alpha either 0 or 255, precomputed or set up in a pixel shader).