All Things Mopar wrote:
Today Roger N. Clark (change username to rnclark) spoke these
views with conviction for everyone's edification:


Enlarging and shrinking an image requires interpolation.
ALL interpolation algorithms have artifacts, at least all
I've seen. If you compare your original small image with
the largest one, you can see artifacts. I'll point out
one.


Resampling using any algorithm, interpolation or simple pixel
resize, can and does produce damage. But the term "artifact"
first came to prominence during the early experiences with
JPEG, after people first saw the damage from over compression.

Artifacts in digital imaging is much older than jpeg. I learned
of it in the 1970s in graduate school. Yes digital imaging was
being done back then, pre CCDs. I was using a vidicon,
256x256 if I remember correctly, system that digitized with
electronics filling 6 feet of rack space, and a fifty pound camera
head, cooled to dry ice temperatures.

Being that I'm a visual sort of a guy, I don't know how to use
the analytical tools in PSP 9 to examine an image, and I don't
parlez vous PS CS. So, I'm very curious to know how you can
tell that your examples above were caused by interpolation and
not the more likely cause, over compression at some point,
and/or multiple open/edit/re-save cycles.

Without knowing the exact techniques and algorithms used in the
processing, one can't be sure of where things were introduced versus
where they were exaggerated. In my experience with scientific
interpolation, including writing imaaging interpolation algorithms, it is
my experience that there is no perfect interpolation algorithm for
this type of problem. What is the likely cause is that the interpolation
in the upsizing is imperfect (causing the fundamental artifact) which
the sharpening and other processing steps enhanced. Some algorithms
invent data (e.g.fractals) which may look good in many cases, but
is scientifically incorrect, thus all the added "information" is
artifacts. Other algorithms try and do little "inventing" linear,
cubic spline and others, but these cause other artifacts. One hopes
the artifacts have minimal detriment to the final image appearance.

Roger