Tim Auton wrote:
"matt" wrote:

Mike Simmons wrote in message ...

I can't explain the math, Pierre, but it makes sense to me in terms of the
amount of information collected. The mistake is in thinking that the
CCD's five available pixels will always record the same thing.

the process of increasing spatial resolution of a CCD sensor beyond its
limit dictated by pixel size is called dithering . It implies moving the
image in sub-pixel steps and taking multiple exposures at these slitghly
changed positions .

For details see:
http://www.stsci.edu/instruments/wfpc2/drizzle.html

However the Drizzle algorithm was developed for use with
*under*-sampled images. I don't think it claims resolution of high
spatial frequency detail beyond the limitations imposed by the optics
of the instrument (Rayleigh criterion, Dawes limit or Sparrow limit -
but that's another argument).

No but some of the deconvolution techniques in routine use now for the
past couple of decades can and do. The worry is that they can also
produce artifacts if used improperly. They are a double edged sword.

The Titan image apparently shows spatial resolution at a frequency
higher than the Sparrow limit of the instrument. Show me a
peer-reviewed paper that says that is possible in the general case and
I might believe it's not noise.

It isn't possible in the general case. But it is possible with good
signal to noise data on a high contrast target with a well qualified
point spread function. I think the first one is pubically accessible.

Please don't hammer ADS abstracts for downloads unless you really want
to see the deeper mathematical detail. It is not light reading and they
are big files.

See for example:

STSDAS Users Guide
http://stsdas.stsci.edu/documents/SUG/UG_29.html

Tim Cornwell's paper in A&A' on the VLA Maxent deconvolution code VM
http://adsabs.harvard.edu/cgi-bin/np...1a5e6d34902655

NASA data analysis team peer reviewed article
http://adsabs.harvard.edu/cgi-bin/np...1a5e6d34902655

There *are* reasons to worry about the detail on a bright planetary disk
if the deconvolution code is allowed to overfit the data. It may cause
ringing effects on edge transitions that can lead to spurious artefacts.
And I suspect that some of these examples have been overcooked.

The bright ring round the left edge of Jupiter on the following example
is almost certainly due to overfitting the data (or algorithmic
instability).

http://www.buytelescopes.com/gallery...o.asp?pid=2073

Regards,
Martin Brown