1. An apparatus configured to generate a high sensitivity image, the apparatus comprising: an image dividing unit configured to divide an image into a first image comprising a low frequency component and a second image comprising a high frequency component; a first image processing unit configured to determine a brightness variance value of the first image based on an ISO sensitivity expansion value and a mean pixel value of the first image, and apply the determined brightness variance value to each pixel of the first image to change a brightness of the first image; a second image processing unit configured to restore details of the second image; and an image synthesizing unit configured to synthesize the first image comprising the changed brightness with the second image comprising the restored details.