1. A measuring method for measuring contrast of a display device, comprising: controlling the display device to display a first image, measuring brightness of a central area of the first image, and obtaining a first brightness, wherein the first image includes a maximum gray scale area and at least one non-maximum gray scale area, and a test area of the first image is disposed in the maximum gray scale area; controlling the display device to display a second image, measuring brightness of a central area of the second image, and obtaining a second brightness, wherein the second image includes a minimum gray scale area and at least one non-minimum gray scale area, and a test area of the second image is disposed in the minimum gray scale area; and determining the contrast of the display device according to the first brightness and the second brightness.