1. An imager, comprising: an optical system for imaging; a focal plane array for capturing images imaged by the optical system, wherein the images each comprise a plurality of values for each pixel in the focal plane array; and a memory containing a plurality of first numerical coefficients for a first spatial filter, wherein the first numerical coefficients represent a first distribution of parasitic energy in a first section of the images and the first spatial filter is applied to correct relative values of the pixels in the first section of the images.