A method for digital processing comprises receiving a first set of image data corresponding to a first time and a second set of image data corresponding to a different time. Intensity values for each of a first pixel and second pixel are extracted from each of the first and second set of image data. Substantially linear values in a plurality of intensity values are identified for each of the first and second pixels. For each of the first and second pixels, regression is performed on each of the substantially linear values in the plurality of intensity values. The regression may calculate an intensity level as a function of exposure time. The regression may generate slopes corresponding to the linear values for each of the first and second pixels. These slopes more accurately represent the actual ratio of intensity values. The ratios are useful in applications, such as, for example, polarization.