1. A method of performing gamma correction for liquid crystal display (LCD) panel, comprising: Step A 1 : dividing a display area of a LCD panel to form n sub-areas of the display area, where n is a positive integer equivalent to or larger than 2; Step A 2 : dividing all grey-scale images into n sets to form n sets of grey-scale images, where each set of grey-scale images, comprising a plurality of grey-scale images, corresponds to one specific sub-area; Step A 3 : displaying a first chosen grey-scale image of each set of grey-scale images on the corresponding sub-area of n sub-areas concurrently, where the first chosen grey-scale image is any one of the grey-scale images in the set of grey-scale images; Step A 4 : detecting a brightness of the first chosen grey-scale image with photosensors installed on the sub-areas; Step A 5 : examining if there is grey-scale image pending for detection in the set of grey-scale images, wherein the grey-scale image pending for detection was not the first chosen grey-scale image; if there is grey-scale image pending for detection, then replace the first chosen grey-scale image with the grey-scale image pending for detection in the set of grey-scale images, and continue with step A 3 ; if there is no greyscale image pending for detection, then continue with step A 6 ; Step A 6 : extracting a gamma curve of the LCD panel based on the grey-scale and brightness of the first chosen grey-scale images; and Step A 7 : correcting the gamma curve of the LCD panel based on a pre-defined gamma curve; wherein the step A 3 comprises: displaying the first chosen grey-scale image of the set of grey-scale images from images at the highest grey-scale level to the lowest grey-scale level, or from images at the lowest grey-scale level to the highest grey-scale level on the corresponding sub-area; and the step A 4 comprises: Step A 41 : installing a photosensor in the middle of the sub-area and sticking the light-receiving surface of the photosensor on the sub-area; Step A 42 : detecting an analog signal of the brightness of the first chosen greyscale image with the photosensor; and Step A 43 : converting the analog signal of the brightness of the first chosen greyscale image into a digital signal of the brightness of the first chosen grey-scale image, wherein the step A 7 comprises: Step A 71 : examining difference in brightness of each grey-scale image between the gamma curve of the LCD panel and the pre-defined gamma curve; Step A 72 : performing brightness compensation based on the difference in brightness of each grey-scale image so to acquire a brightness compensation value; and Step A 73 : correcting the gamma curve of the LCD panel with the brightness compensation value.