1. A vehicular imaging system comprising a photosensor array comprising a plurality of photosensor elements, said photosensor array having a field of view forward of the vehicle that is generally in line with the vehicle's primary direction of forward travel, said photosensor array capturing images of an area encompassed by said forward field of view; a control responsive to an output of said photosensor array, said control processing an image data set indicative of captured images; wherein said control processes a reduced image data set of said image data set to determine whether an object of interest is within a target zone of said captured image, said reduced image data set being representative of a portion of said captured images as captured by a particular grouping of said photosensor elements; and wherein said control adjusts said reduced image data set so as to be representative of a portion of said captured images as captured by a different particular grouping of said photosensor elements, said control adjusting said reduced image data set in response to a determination of a change in a focus of expansion of said captured images; wherein said focus of expansion comprises at least one photosensor element that initially detects a new light source in said field of view, and wherein said control tracks said new light source as it approaches the subject vehicle to confirm that said new light source is indicative of an object of interest, wherein said control compares a location of said new light source to an expected location of the light source to determine if there is an offset, said control adjusting said reduced data set in response to determination of said offset.