1. A method of fast motion estimation for video pre-processing, comprising the steps of: (A) selecting 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 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 a fast motion estimation search including the steps of: (i) performing 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 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 the better reference image portion as the candidate best reference image portion; (iv) repeating 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 the candidate best reference image portion as the best reference image portion; and (vi) calculating a motion vector from the best reference image portion.