Quantitative Light Measurement?

[fotofun]

This might be a bit of an odd request, but here goes;

I'm working on a biology experiment measuring bioluminescent algae. What I want is some way to quantitatively (or with some kind of graph/chart) measure the light produced by the algae. We don't have any equipment to measure it in the laboratory (high school science budget), so my idea is to take digital photographs of the different trials and analyse them on the computer.

Does anyone know of any software/techniques to measure the overall brightness of a digital image? Any help is much appreciated.

 

[astrostu]

To do it right, there are several steps. You're basically trying to do photometry. Rather than me writing an extremely long post, look at my page on astronomical imaging here: http://burro.astr.cwru.edu/stu/me/photos/processing.html . It will not be 100% applicable, but everything about calibration images and detector and telescope (AKA lens in this case) imperfections will be important.

After that (or not if you don't care about it), you basically need software that will do image arithmetic since you want to add up (discrete integral) all the light in a certain part of your image. There's software out there to do it, but none that I know of that's free (IDL is the one that comes to mind at the moment).

Alternatively, you could do a "poor-man's" (or woman's) photometry. Assuming you have Photoshop or some software that will tell you the intensity (e.g., RGB values) of a given pixel, you can simply look at the intensity in a certain number of pixels for each photograph and take the average.

 

[The_Traveler]

Alternatively, you could do a "poor-man's" (or woman's) photometry. Assuming you have Photoshop or some software that will tell you the intensity (e.g., RGB values) of a given pixel, you can simply look at the intensity in a certain number of pixels for each photograph and take the average.

Interesting thought.
Wouldn't one have to use a unaltered raw file?

 

[astrostu]

Wouldn't one have to use a unaltered raw file?

Or ensure that all the files were processed the same way, the photos were taken with the same settings, and the camera wasn't moved.