[coldtea]

>Ponder for a second the phrases, "filtered water", "coffee filter", "camera filter", etc. In all of those cases, you are interested in the set without the filtered thing, not with.

Filtered is akin to "cleansed" (it refers to the "main body") not akin to "picked out" (which would have applied to the undesirable elements.

It's actually the water (or the light, in the case of camera filter) that's filtered (hence the name "filtered water" and not "filtered dust and detritus").

The other stuff is not what's being filtered -- just what's "filtered out".