An image adjusting method for extending vertical blanking intervals of an image signal is provided. Using the image adjusting method, an adjusted image signal is synchronized with an image signal before the adjustment to prevent image delay. The image adjusting method comprises providing a first image signal having a first data enable signal, wherein the first data enable signal has a first data enable duration; and generating a second data enable signal having a second data enable duration. The first and second data enable durations correspond to a same image frame of an image signal, and the second data enable duration substantially overlaps the first data enable duration.