1. An over-drive value generating apparatus, applied to a display device, comprising: a pixel value converting unit, for generating a converted pixel value for a pixel according to a current pixel value of a current image for the pixel and a previous pixel value of a previous image for the pixel; a gain generating unit, for generating a gain according to a position of the pixel; and a calculation unit, for generating an output pixel value according to the current pixel value, the converted pixel value, and the gain.