Re: Curious about correcting exposure times for time-series imagesets
Posted by
Gluender-3 on
Feb 16, 2010; 10:12am
URL: http://imagej.273.s1.nabble.com/Curious-about-correcting-exposure-times-for-time-series-imagesets-tp3689371p3689372.html
Chris,
besides your core question and because you are using a consumer camera:
Did you compensate for this camera's gamma?
Before you do any scientific image analysis or processing, make sure
that the image data doesn't suffer from any nonlinear transduction
process.
>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
Best
--
Herbie
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