1. A method for enhancing an image quality of a two-dimensional (2D) ultrasound image, comprising: acquiring a 2D ultrasound image using an ultrasound diagnostic device decomposing the 2D ultrasound image into a plurality of images having a multi-resolution by N levels, wherein N is a positive integer; computing a tangential direction vector and a normal direction vector of each pixel in the decomposed image, comparing a magnitude difference between the tangential direction vector and the normal direction vector with a threshold value, and determining characteristics of each pixel in the decomposed image based on the comparison result; enhancing the decomposed image based on the pixel characteristics; composing 1 st -level composition for the decomposed image; and repeatedly performing the computing, enhancing, and composing steps until a size of the composed image is identical to that of the 2D ultrasound image.