Best algorithm to downscale images for buttons/icons?

[eil]

Can smbd please give some hints and advices for best settings to get better quality downscaled images? I'm talking about real small sizes, like downscaling 512/256/128px PNG into some 24/16px, to be used for icons and buttons.
My own experiments with settings didn't really bring any different results and sharpness/recognition drops a lot. Checked XnResize, but it seem to have pretty same algorithms as main MP does.

While trying to search through forum, i stumbled upon opposite "problem", with user searching for upscale methods here(viewtopic.php?p=202448#p202448) = may it happen smbd knows some similar stand-alone/not-web-dependant downscale project?