1. A method for analyzing noise content in a digital image, comprising: using a computer to perform: sampling regions of the digital image; discarding sampled regions that do not satisfy a pre-specified condition, wherein said discarding sampled regions that do not satisfy the pre-specified condition involves: discarding sampled regions that are underexposed or overexposed; computing the variance of the pixel values in each remaining sampled region; and discarding sampled regions where the variance is above a pre-specified value; extracting noise information from each remaining sampled region; and generating a mathematical model of the noise using the noise information.