Curious about correcting exposure times for time-series imagesets

Posted by Kinata on Feb 16, 2010; 6:03am
URL: http://imagej.273.s1.nabble.com/Curious-about-correcting-exposure-times-for-time-series-imagesets-tp3689371.html

Hi...
I have several series of time-lapse photos of transport of fluorescent dye
in leaves, 120 pics/series.
Wanting to measure increase of dye in a leaf overall by counting the number
of pixels containing
beyond a certain threshold of that dye color.

We've been driving a Canon A40 camera with remote-control software that let
us set everything
but exposure time. Didn't think that there would be much variation in this,
but it turned out that
exposure times ranged from 1 sec (darkroom, UV light) to about 1/20sec. This
has pretty much
leveled the dye data overall, unfortunately.

I've written batch processing code for extracting EXIF data from each JPEG
image for the exposure
time. Questions:

1) Assuming that the best approach would be to decrease the image brightness
inverse-proportionally
to exposure time, is there a "sanctioned" algorithm for doing this? If we
could do this over again, I
would include a reference card (white, 50% gray, black) in each pic  for
equalizing levels. Instead,
thinking that I'll use a rectangular region in the image that should be
invariant across each series,
and equalize with that even though it's not grayscale.

2) It doesn't seem that equalizing histograms would be viable, as the images
get brighter as the
dye migrates through each leaf.

2) Is there a better way to do this? Dare I hope that someone has done a
plug-in for this?

Regards,
Chris