1. In a display system, a hue dividing and judging device being used for dividing hue of a color space into j color areas and for judging that the hue of a pixel of an input image falls into which one of the j color areas, the device comprising: a memory unit for storing a look-up table, the look-up table recording N boundaries including j+1 operative boundaries for defining the j color areas, N being a natural number, j being an integer ranging between 1 and N−1; a calculation module for calculating the hue of the pixel of the input image; and a judgment module, according to the j+1 operative boundaries recorded in the look-up table, for judging that the hue of the color space is divided into the j color areas and for judging that the hue of the pixel is between which two of the j+1 operative boundaries, so as to judge that the hue of the pixel of the input image falls into which one of the j color areas.