Provided is an image sensor that can solve the limitation in expanding an output dynamic range, which is caused when a uniform gain contrast scheme is applied, and prevent the reduction of an input dynamic range, thereby stably adjusting the distribution of image brightness. The image sensor includes a contrast gain adjuster for adjusting a brightness distribution of an image detected from a pixel array by controlling a contrast gain of an inputted pixel data. The contrast gain adjuster calculates a minimum brightness value of a dark region and a maximum brightness value of a bright region from the image brightness distribution, the dark region and the bright region being divided according to a set reference value.