model to obtain a distortion coefficient r c r d 1 kr 2 d 0 lt k u2266 a u2212 1 r 2 dm 1 where r c is a distance from a predetermined point to the origin of a coordinate system of a corrected image r d is a distance from the predetermined point to the origin of a coordinate system of a distorted image r dm is a maximum distance from the origin of the coordinate system of the distorted image to an outermost point k is a distortion coefficient and a is a constant greater than 2 according to the lens distortion model an optimal distortion coefficient k is manually measured within a predefined measurement range without using auto estimation in order to remove an error caused by noise that a conventional method encounters that is an optimal distortion coefficient within a predefined range which allows an image received through the wide angle lens 100 to be the same as an image perceived by human eyes is obtained manually for increased precision the lens distortion model may use higher order terms including a plurality of distortion coefficients however increasing the number of distortion coefficients may increase the errors introduced during the distortion coefficient measurement thus increasing subsequent numerical calculation errors accordingly the apparatus of fig3 uses only one distortion coefficient because the radial distortion can be sufficiently modeled with only one distortion coefficient as shown in equation 1 the lens distortion model used by the apparatus of fig3 includes only one distortion coefficient since the present invention assumes that distortion is radial distortion an optimal distortion coefficient is a positive.