1. A system for selecting a pixel block within an image frame for use in motion estimation and embodied in a video encoder for encoding a video data stream, comprising: a pixel block processor for, selecting a pixel block of a predetermined size within an image frame encompassing a plurality of pixel blocks; determining boundaries of an extended pixel block encompassing the selected pixel block and additional pixels of an overlapped region; deriving statistical information for said selected pixel block and statistical information for said additional pixels of said overlapped region; and selecting said selected pixel block when said derived statistical information for said additional pixels of said overlapped region has a value less than a product of the derived statistical information of said selected pixel block and a first parameter having a value between zero and one; and selecting said extended pixel block when said derived statistical information for said additional pixels of said overlapped region has a value greater than a product of the derived statistical information of said selected pixel block and a second parameter having a value greater than one.