1. A method for adjusting a target gray level of a target pixel based on a spatial mask, the target pixel being surrounded with N adjacent pixels, N being a positive integer, each of the N adjacent pixels respectively having an adjacent gray level, said method comprising the steps of: (a) multiplying the target gray level with a sharpness index to generate an amplified target gray level and respectively multiplying each of the adjacent gray levels with an adjacent index to generate N modified adjacent gray levels, wherein the sharpness index and the adjacent index are related to the spatial mask; (b) adding up the amplified target gray level and the N modified adjacent gray levels to generate a first gray level sum; (c) multiplying the first gray level sum with a multiplying parameter to generate a second gray level sum, wherein the multiplying parameter is related to the spatial mask; and (d) dividing the second gray level sum by a dividing parameter to generate an adjusted gray level for the target pixel, wherein the dividing parameter is related to the spatial mask.