1. A method of determining an image noise estimate value in a digital video processing system using only a single video image, the method comprising the steps of: providing a plurality of predetemined SAD value ranges, each predetermined SAD value range corresponding to a prospective image noise estimate value; determining, in a concurrent manner, if a SAD value calculated in the video image falls within one or more of the predetermined SAD value ranges; repeating the determining step for other SAD values calculated in the video image; for each one of the prospective image noise estimate values, counting the number of SAD values that fall within that prospective image noise estimate value's corresponding predetermined SAD value range; selecting, as the image noise estimate value, the prospective image noise estimate value that has a count value which meets predetermined criteria.