An imaging system divides image pixels intensities by exposure time to generate image data in units of intensity per time. In some embodiments, the imaging system divides a fluorescent light image in intensity per time units by an excitation light image in intensity per time units to provide a quantitative corrected fluorescent light image that is generally invariant to position of an imaging instrument relative to a biological tissue being imaged. In other embodiments, the imaging system combines the fluorescent light image in intensity per time with attenuation corrected distance values.
