The Lanczos scaling is of very good quality, but it's rather slow,
which can be very noticeable with large images, so it's not a very
good default for everything. And in general, it's not good to refer
to a specific algorithm when all one usually wants is fast/default/best.

Some of these changes are a bit of a guess between default/best,
but the general logic is that best should be used only for images
that won't be large or where the possible waiting does not matter.

Change-Id: I53765507ecb7ed167890f6dd05e73fe53ffd0231