1. A color interpolation method, comprising: defining a pixel group of a matrix structure, having a center pixel to be color-interpolated, in an image passed through a color filter of Bayer pattern and detected by an image sensor; determining whether an edge of the image exists or not in the pixel group; when an edge does not exist in the pixel group, interpolating a color value of the center pixel using a low pass filter; and when an edge exists in the pixel group, interpolating a color value of the center pixel according to edge directivity of the edge, wherein said defining comprises: defining the pixel group of a 5×5 matrix structure, which has 5 rows in a horizontal direction and 5 columns in a vertical direction, in which 5 pixels are positioned in each row and each column of the matrix structure and a pixel to be color-interpolated is the center pixel; defining the pixel group as a first type pixel group, in which a color detected from the center pixel in the pixel group is green and a pixel from which red is detected is disposed in the row containing the center pixel; defining the pixel group as a second type pixel group, in which a color detected form the center pixel in the pixel group is green and a pixel from which blue is detected is disposed in the row containing the center pixel; defining the pixel group as a third type pixel group, in which a color detected from the center pixel of the pixel group is red; and defining the pixel group as a fourth type pixel group, in which a color detected from the center pixel of the pixel group is blue, wherein said interpolating using the low pass filter comprises interpolating the color value of the center pixel by the following Equation 2: Equation 2 for the first type pixel group: 
 G 33_inter=(4 ·G 33+2 ·G 22+2 ·G 24+2 ·G 42+2 ·G 44 +G 13 +G 21 +G 25 +G 53)/16 
 R 33_inter=(2 ·R 32+2 ·R 34 +R 12 +R 14 +R 52 +R 54)/8 
 B 33_inter=(2 ·B 23+2 ·B 43 +B 21 +B 25 +B 41 +B 45)/8; for the second type pixel group: 
 G 33_inter=(4 ·G 33+2 ·G 22+2 ·G 24+2 ·G 42+2 ·G 44 +G 13 +G 21 +G 25 +G 53)/16 
 B 33_inter=(2 ·B 32+2 ·B 34 +B 12 +B 14 +B 52 +B 54)/8 
 R 33_inter=(2 ·R 23+2 ·R 43 +R 21 +R 25 +R 41 +R 45)/8; for the third type pixel group: 
 G 33_inter=( G 23 +G 32 +G 34 +G 43)/4 
 R 33_inter=(4 ·R 33 +R 13 +R 31 +R 35 +R 53)/8 
 B 33_inter=( B 22 +B 24 +B 42 +B 44)/4; and for the fourth type pixel group: 
 G 33_inter=( G 23 +G 32 +G 34 +G 43)/4 
 B 33_inter=(4 ·B 33 +B 13 +B 31 +B 35 +B 53)/8 
 R 33_inter=( R 22 +R 24 +R 42 +R 44)/4, where Gmn is a green color value of a pixel of m th row and n th column, Rmn is a red color value of a pixel of m th row and n th column, Bmn is a blue color value of a pixel of m th row and n th column, G33_inter is an interpolated green color value of the center pixel, R33_inter is an interpolated red color value of the center pixel, and B33_inter is an interpolated blue color value of the center pixel.