Loosing Particles when Rotating Image

Posted by Brendan H. on Nov 07, 2007; 5:57pm
URL: http://imagej.273.s1.nabble.com/Loosing-Particles-when-Rotating-Image-tp3696797.html

I have a series of images where a few thousand tiny particles form a circular ring, and I need a
way to count the number of particles in a discrete fashion; i.e. form a 5 degree selection wedge
(using the center of the ring as the vertex, and half the image width, which is slightly larger than
the ring diameter, as the radii) that includes 5 degree's worth of particles, count them, then rotate
the wedge by 5 degrees, and iterate.

I'm having some troubles getting this to work however.  My first idea was to make the wedge,
count the particles, rotate the image, and reiterate.  This keeps the wedge stationary, but "sweeps"
the image past the selection, eventually counting all the particles in discrete steps.  I got the
macro to work fine, but I noticed a few things:

1) When I rotate the image arbitrarily without iterating, I loose a bunch of particles each time.  E.g.
when I do a total particle count before rotation, I get 1669 particles, but after one arbitrary
rotation (43degrees in this case) the particle count drops to 1557.  My ring is centered in the
square window, so the particles are not leaving the field of view; also 90 degree rotations do not
yield a flux in the number of particles.  I noticed this problem because as I ran the macro, the
particles got more "clumpy" with each small rotation; it's clearly an additive issue.

2) If I iterate when rotating, I have to re-threshold every rotation.  This has the same clumping
effect (although much more severe) as the simple rotation.

Anybody have any ideas?  I'm pretty stuck on this!!

Thanks for your help,
Brendan Hermalyn