1. A method of fast motion estimation for video pre-processing, comprising the steps of: (A) selecting, using a microprocessor, a second-order distortion criterion for identifying a best reference image portion for comparison with a current image portion, said second-order distortion criterion being a Lagrange-optimized combination of a mean squared error criterion with an entropy criterion; (B) using said second-order distortion criterion to select, using a microprocessor, an initial reference image portion as an initial starting point for a motion estimation search, said initial starting position being chosen based on at least one motion vector from a neighboring image portion; and (C) performing, using a microprocessor, a fast motion estimation search including the steps of: (i) performing, using a microprocessor, a diamond search starting from said initial reference image portion using said second-order distortion criterion to identify a candidate best reference image portion; (ii) performing, using a microprocessor, a nearest neighbor search starting from the candidate best reference image portion using said second-order distortion criterion to identify either the candidate best reference image portion or a different neighboring reference image portion as a better reference image portion within a search range limited by an adaptive search range cap; (iii) re-identifying, using a microprocessor, the better reference image portion as the candidate best reference image portion; (iv) repeating, using a microprocessor, said steps (ii) and (iii) until in said step (ii) either (a) the candidate best reference image portion is identified as the better reference image portion so that said second-order distortion criterion cannot be improved, or (b) any further search would exceed the adaptive search range cap; (v) identifying, using a microprocessor, the candidate best reference image portion as the best reference image portion; and (vi) calculating, using a microprocessor, a motion vector from the best reference image portion.