1. An apparatus for processing a target video frame comprised in a video stream comprising M input pixels, M being a positive integer, each of the M input pixels respectively having an input gray scale, said apparatus comprising: a gain generating module for generating, in accordance with the input gray scales of the M input pixels, a contrast gain and a minimum input gray scale; a contrast enhancing module for adjusting, in accordance with the contrast gain and the minimum input gray scale, the input gray scales of the M input pixels to generate an intermediate image comprising M intermediate pixels which each respectively has an intermediate gray scale; and a Gamma adjusting module for adjusting, in accordance with the contrast gain, the intermediate gray scales lower than a first threshold and for outputting the adjusted intermediate image as an output image.