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Hi List, Hi Mark,
just my 2 cents:
The way i like to look at it, if the square pixels on the camera chip
are smaller than the magnified (by the objective and other optics)
size of the light wavelength or point spread function, which is the
case in a microscope at high magnification and pixels of a few
microns, then the pixels must act as point samples. Each photon could
hit one of several pixels, so the fact they are square is irrelevant.
What does matter is they they are on a square grid... but thats only
accidental.

on a point scanning confocal, remember that the x direction scans in a
continuous sweep, buy the y direction goes in jumps, like the z
direction.
If images are under sampled (pixel spacing bugger than PSF), there can
be gaps in the information between y lines and z slices... but
interestinggly not x as its swept.
In the araay of square pixel on the computer screen, one is totally
unaware of that problem!!!

This is the pixel is not a little square argument, just rephrased:
If the PSF is bigger then the pixel spacing.... then pixel act as
point samples. If PSF is smaller them pixel spacing... then indeed the
shape of the detector element (dexel) is a useful thing. Most of the
time, for properly spatially sampled optical microscopy images, we
make sure the PSF is 3x or so bigger then the pixel spacing.

If the pixel grid was hexagonal, would pixel be little hexagons in our
usual slightly over sampled case...? No.

Pixels can be treated as squares only when the PSF is small compared
to the pixels (i prefer "dexel" - detector element - to distinguish it
from pixels in the image.. which are often point samples - picture
elements, or pixels on  a computer screen). Eg in a cheap camera
taking a non diffraction limited photo.
Not the case with us.

The pixel data in most of our images is point like, and when it is, to
treat it otherwise can give wrong results in image resizing etc. Not
good.
See the Fiji Downsample plugin page:
http://fiji.sc/Downsample

Date:    Sat, 14 Apr 2012 14:26:35 +0100
From:    Mark Cannell <[log in to unmask]>
Subject: Re: Nyquist and Image size

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That's a nice 'rant' but it does of course ignore the fact that many =
cameras have square pixels... so it is justified to represent/describe =
the data with square pixels in that case ... I kind of wish that =
Microsoft applied similar 'deep thought' to their software before =
releasing it tho'

LOL

As a further aside,  I note that no one has so far discussed the issue =
of A/D conversion resolution in deciding the _actual_  bandlimit. For a =
n bit converter, the bandlimit occurs when the power spectrum of the =
Airey disk falls below 1/2 a bit (I think) so it's also amplification =
and noise dependent...

Cheers
Mark

--
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