1. A bit-resolution-extension method comprising: normalizing upper n-m bit values of adjacent pixels based on an upper n-m bit value of each pixel of a sample image; analyzing a statistical distribution of a lower m bit value of a reference pixel by patterns of a set comprising the normalized adjacent pixels; generating a memory address from normalized adjacent pixel values of the sample image; saving a representative value of the lower m bits by patterns to the memory address generated as a result of the analyzing; normalizing adjacent pixel values based on each pixel value of an input image; generating the memory address from the normalized adjacent pixel values of the input image; reading the representative value of the lower m bits saved in the memory address; and adding the read lower m bits to the input image pixel values as lower bits.