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.