1. A method for generating an image, comprising: receiving a first image that is acquired during a first exposure period and defining the first image as a reference image; defining multiple reference regions of interest within the reference image, wherein an aggregate number of pixels within the multiple reference regions of interest is substantially smaller than a number of pixels of the first image; receiving a second image that is acquired during a second exposure period; and updating the reference image in response to content of the reference image, content of the second image and a first type of spatial relationship defined between the reference image and the second image; wherein a shift is defined in response to multiple spatial relationships between the multiple reference regions of interest and between multiple regions of interest of the second image.