Surface generation and positional gain adjustment techniques for an imager are described. Embodiments of the techniques use zones having flexible boundaries which can be reconfigured depending upon the type of lens being used in a given application. Each pixel within each zone is multiplied by a correction factor dependent upon the particular zone while the pixel is being read out from the array. The correction factors comprise coefficients that are different for each color channel and in some instances different for each corner of each color channel.