1. A vision system of a vehicle, said vision system comprising: a camera disposed at a vehicle and having a field of view exterior of the vehicle; wherein said camera comprises an imaging array having a plurality of photosensing elements arranged in a two dimensional array of rows and columns; wherein said imaging array comprises a plurality of sub-arrays comprising respective groupings of neighboring photosensing elements; an image processor operable to process image data captured by said camera; wherein said image processor is operable to perform a discrete cosine transformation of captured image data; wherein a result of the discrete cosine transformation is put into a K-Means classifier; wherein a Markov model compares at least one sub-array with a neighboring sub-array; and wherein said image processor is operable to adjust a classification of a sub-array responsive at least in part to the discrete cosine transformation and said Markov model.