Posted by
Janne Hyötylä on
Feb 15, 2011; 10:42am
URL: http://imagej.273.s1.nabble.com/affordable-camera-suggestions-tp3685628p3685638.html
Hi all,
On Mon, 14 Feb 2011 23:41:38 +0100, David Gene Morgan
<
[hidden email]> wrote:
One could obviously over-sample by a factor of (say) 5 and not even
> think about sampling issues having an effect on feature resolution.
> However, the 5x over-sampled image has 25x more pixels, and takes 25x
> more computer memory, storage space, etc. This massive over-sampling
> can be the "empty resolution" that people sometimes mention (though
> other types of empty resolution are also possible). Over-sampling at
> 1.5x only increases things by a small factor (2.25x) and still results
> in virtually no loss of feature resolution (and no empty resolution).
With today's computers the memory and storage issues are probably not so
important anymore.
I think the most critical issue is that with more pixels (ie. smaller
pixel size) the amount of photons per pixel decreases, and this decreases
the signal-to-noise ratio.
> The above discussion is certainly the root of the of "3x sampling"
> commonly mentioned in the cryo-electron microscopy field, and I suspect
> it plays a major part in the sampling schemes of most other digital
> imaging processes. LOTS of other things affect the resolution in a
> digital image, and these can be as important as what is discussed here.
> But since it is theoretically impossible to get resolution that is
> better than 1/(2x) from an image sampled in steps of x, one is most
> often better served by sampling a bit more finely: If one wants a
> resolution of 1/Q, sample at Q/3 instead of Q/2!
You can also see a geometrical derivation that leads to a minimal sampling
of 2.8x optical resolution in Pawley's Handbook of biological confocal
microscopy:
<
http://books.google.com/books?id=IKcPnaNPrhoC&lpg=PA64&ots=r8SqLx2avr&dq=nyquist%202d%20sampling&pg=PA65#v=onepage&q&f=false>
I have also seen 2.3x mentioned that was apparently also somehow derived
from Nyquist for 2D signals, but without the actual derivation.
So while 3x might be "anecdotal", it is not far away from mathematically
derived values.
Best,
Janne