An overdrive device includes a training unit, an analysis unit and a Contrast adjustment unit. The training unit establishes a luminance difference look-up table (LUT) having an R2 number of luminance differences. Each of the R2 number of luminance differences represents a luminance difference between a measured display luminance value and a target luminance value of a display device when each of first and second viewing angle images correspond to any value of a grayscale range R. With respect to first and second viewing angle input image data, for pixel data therein corresponding to a same pixel position, the analysis unit looks up the luminance difference LUT to obtain a looked-up luminance difference, and accordingly calculates a luminance difference index. The contrast adjustment unit partially adjusts the grayscale of the second viewing angle image according to the luminance value index to obtain headroom for an overdrive operation.