A bit-resolution-extension method is provided. The resolution extension method includes normalizing n-m upper 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 the reference pixel by patterns of a set consisting of 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 as a result of the analysis, normalizing adjacent pixel values based on each pixel value of an input image, generating the memory address from the normalized adjacent pixel value of the input image, reading a 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.