Kevin McMurtrie wrote:
Factor of two resampling is trivial. It's the other ratios that tend to
produce beats where pixels go in and out of phase with the original.
Various algorithms attempt to reduce the beats without blurring the
image too much. One trick is to find image edges and nudge them into
alignment with the destination pixels, but that only creates a different
kind of distortion.

Kevin,

You may be right about a factor of 2, but what about a factor of 2^k? I
know that when I ask Photoshop to zoom something 800%, it doesn't do a
very good job. I am really looking at the case of high zoom (like 800%
or 1600% or 25600%). If you are telling me that 2^k is trivial, then I
do not agree.

I'm not really touching on the issue of resampling by a factor between
70% and 141%. You're right that frequencies in the original image will
beat in a resampling, but there is nothing much you can do about that
(unless, as you say, you distort the original). I'm taking it as
granted that resampling in this range has its own issues, but basically
gives acceptable results except in singular cases. It's the poor
performance for large factors that I'm targeting.

John