1. A displacement estimation device, for use in estimating a displacement vector from a first pattern in a first original image to a second pattern in a second original image, wherein each original image includes a plurality of pixels, said device comprising: a vector calculator calculating at least a first parameter for a first pixel in said first original image and at least a second parameter for a second pixel in said second original image, said first and second parameters integrating, respectively, the information of: (a) the intensities of pixels in a region of interest surrounding said first and second pixels, and (b) the relative distances from said surrounding pixels to said first and second pixels; a displacement calculator electrically connected with said vector calculator, and calculating said displacement vector based on said parameters calculated by said vector calculator for said first original image and said second original image; and a vector processor electrically connecting with said vector calculator and said displacement calculator, wherein said vector processor categorizes said plurality of pixels of each said original image into two or more groups according to the parameter of each of said plurality of pixels, and assigns a different number to each group as a gravity index; and wherein said displacement calculator calculates said displacement vector based on a gravity displacement (S) which is a normalized displacement between gravities of said gravity indices of said first and second original images, wherein said gravity displacement (S) is calculated by: 
 S =[Index_Gravity( x i, y i ) n −Index_Gravity( x i , y i ) n−1 ]/ NF i wherein Index Gravity (x i , y i ) n−1 and Index Gravity (x i , y i ) n are, respectively, the gravities of the gravity indices of the (n−1)th original image and the nth original image, and NF i is a normalization factor, which are obtained from the following equations: Index_Gravity ⁢ ( x i , y i ) n = [ ∑ j = 1 P ⁢ f ⁢ ( x j ) ⁢ δ ⁢ ( index j n - i ) , ∑ j = 1 P ⁢ f ⁡ ( y j ) ⁢ δ ⁡ ( index j n - i ) ] NF i = ∑ j = 1 P ⁢ [ δ ⁡ ( index j n - i ) - δ ⁡ ( index j n - i ) ⁢ δ ⁡ ( index j n - 1 - i ) ] wherein f(x)=x; f(y)=y; i is the gravity index; index j n is the gravity index of the jth pixel, and the value of the function δ(index j n −i) is 1 if index j n−i= 0, otherwise 0; and P is the number of pixels included in the nth original image.