1/ Personal preference, FS is perfectly fine, I just tend to prefer Riemersma, as it tends to look slightly more organic
.
2/ What filtering? ^^ The bg/extent/gravity triplet's sole purpose is letterboxing, because I abhor stretching.
3/ Any kind of input is fine. JPG as an output is *NOT*
.
4/ To do scaling in a linear color space. c.f., the IM documentation.
5/ Nope.