[ImageJ-devel] ROI -> Overlay bug

Michael Doube michael at doube.net
Mon May 14 04:45:45 CDT 2012

Hi Stephan,

> So the PSF is elongated along the
> scanning direction.

No, the PSF is a quality of the optics. The PSF is what is scanned. The
impulse response is what is elongated. The measurement value that the
pixel represents is (in my simplistic understanding of signal
processing) an integral over time of a moving PSF that is varying in
intensity as a function of time. The location of the pixel is calculated
from the scan mirror and stage positions.

> However, that PSF would still be symmetric, except
> if the sensor has a tendency to collect photons only later or earlier
> during exposure.

Such as the situation if the scan is accelerating or decelerating during
acquisition which happens in many designs: one 'side' of the pixel will
tend to be brighter than the other 'side' (one end of the integral will
be longer than the other).

>  So to make my statement clearer, a point sample taken
> from the physical world is almost never a point-sample, but it's
> representative coordinate is most likely not at the top left corner of
> the area between samples.

Agreed, if we want to relate pixels back to the real world in some
reliable fashion (that's the general goal, right?)


More information about the ImageJ-devel mailing list