1. A method of improving gradations of an image carried out by a liquid crystal display including a liquid crystal driving unit for generating a liquid crystal driving signal in response to voltage, which is selected in accordance with the size of an image signal from liquid crystal driving voltages each classified by first and second fields which constitutes a unit frame, and a liquid crystal display panel for being driven in response to the liquid crystal driving signal and displaying the image, the method comprising steps of: (a) measuring luminance levels of an image displayed on the liquid crystal display panel while changing the liquid crystal driving voltage per frame; (b) determining at least one luminance level section whose gradations needs to be improved from the measured luminance levels; (c) producing new liquid crystal driving voltages to be increased or decreased centering around the liquid crystal driving voltage related to lowest luminance level per the first and second fields in each determined luminance level section; (d) obtaining new luminance levels using the produced new liquid crystal driving voltages; (e) selecting at least one available first luminance level from the new luminance levels; and (f) checking whether the gradations of the image are improved using the first luminance level, and/or returning back to step (e) if the gradations are not improved.