A vision system for a vehicle includes an imaging sensor operable to capture an image data set representative of a scene occurring in the exterior field of view of the imaging sensor. A processor processes the captured image data set via an edge detection algorithm, which is applied to a reduced image data set of the captured image data set to detect edges of objects present exteriorly of the equipped vehicle and within a target zone within the exterior field of view of the imaging sensor. The reduced data set is processed more than other image data of the captured image data set in order to detect objects present exteriorly of the equipped vehicle and within the target zone. The target zone encompasses a geographic area of the exterior scene where an object of interest to the driver of the equipped vehicle is realistically expected to be present.