1. An imaging system for a vehicle comprising: an imaging array sensor comprising a plurality of photo-sensing pixels, said imaging array sensor being positioned at the vehicle and having a field of view exteriorly of the vehicle, said imaging array sensor being operable to capture an image of a scene occurring exteriorly of the vehicle; and a control for processing said captured image, said captured image comprising an image data set representative of the exterior scene, said control including a microprocessor comprising an edge detection algorithm, said control applying said edge detection algorithm to a reduced image data set of said image data set, said reduced image data set being representative of a target zone of said captured image, said control being operable to process said reduced image data set more than other image data, which are representative of areas of said captured image outside of said target zone, to detect edges of objects present exteriorly of the vehicle and within said target zone.