1. A method for processing images in a liquid crystal display, the method comprising: (a) acquiring a backlight index in relation to gray levels of an image; (b) adjusting a backlight according to the backlight index; (c) acquiring a reference gray level configured to be compared with the gray levels of the image, wherein the reference gray level varies with a backlight brightness of the adjusted backlight corresponding to the backlight index, and the reference gray level lies in between a first gray level boundary and a second gray level boundary; (d) transferring a gray level of the image into a corresponding output gray level according to a transferring relationship having a first slope when the gray level of the image lies in between the reference gray level and the first gray level boundary; and (e) transferring the gray level of the image into another corresponding output gray level according to a linear relationship having a second slope different from the first slope when the gray level of the image lying in between the reference gray level and the second gray level boundary; wherein the reference gray level is determined by the following equation: X 1 = ( F - 1 ) × N F × BL Max BL Dim γ - 1 wherein X 1 is the reference gray level, BL Max is the backlight brightness when the backlight is completely turned on, BL Dim is the backlight brightness corresponding to the backlight index, γ is a gamma value, N is a highest gray level of the image, and F is a ratio of a highest output gray level compared to the highest gray level of the image.