Re: Laser Beam Profile Analysis in ImageJ

Posted by John Kershaw-4 on Jan 30, 2009; 7:53am
URL: http://imagej.273.s1.nabble.com/Laser-Beam-Profile-Analysis-in-ImageJ-tp3693862p3693863.html

mleigh,

I am doing some similar work with laser line beams in a field application
measuring tree dimensions - so very variable and dynamic conditions.  I've
tested both red and green lasers and think I am going to use green - it is
more visible outside.  I have had some good success with using channel
ratios: 2*red/(green+blue) or 2*green/(red+blue) to make a composite grey
scale image. I use a maximum ratio, then scale everything between 0 and
255.  I have been using a number of line extraction masks to detect lines,
measure height on the photo and length of the line - I am sure there are
similar masks for circles.

JAK (john kershaw)

On Thu, Jan 29, 2009 at 11:01 AM, mleigh <[hidden email]> wrote:

> We are trying to use ImageJ for laser beam profile analysis.  Thus, we want
> to accurately measure power in the beam, and use multiple methods to
> calculate beam diameter.  Also, we are analyzing field tests where the
> background changes from frame-to-frame due to clouds, sun movement, and
> other environmental effects.
>
> So far, I have not found any "laser beam profile" specific plug-ins.  Does
> anyone on the list know of any that have been written?  I have found the
> "Moment Calculator" which calculates the second moment, and thus can be
> turned into a "4 Sigma" beam width.  We are also looking to calculate the
> 1/e^2 width when the distribution is summed in the x and y directions, as
> well as the "90/10" beam width.
>
> Background subtraction is also a problem for us as the built-in "Rolling
> ball" method does not work well for beam images.  Other background
> subtraction methods also do not work as well since we have a dynamic
> background, and we want to preserve the pixel counts in the beam area for
> accurate measurement, and not just make a pretty picture. Right now we are
> taking two regions of interest per frame, and approximating the background
> as constant over the frame.  However, we would like to fit a well-behaved
> function to the background, and subtract off the background on a
> frame-by-frame basis for an entire stack.  We would like to do it sort of
> like it's done in the "A_Posteriori" plug-in, but using a region of
> interest, doing it on an entire stack, and subtracting the background
> without renormalizing the output.
>
> If anyone has any ideas of ImageJ plug-ins that might implement some of
> these measurements, we would really appreciate it.  ImageJ is so much
> better
> and faster than the Ophir/Spiricon BeamStar software we were using.  After
> fighting BeamStar, we are very happy with ImageJ.
>
>
>
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