1. A lens shading correction device in an image sensor, the device comprising: a reference shading data storage unit configured to store reference shading data that include blocked brightness information on each of a plurality of reference images having a different average brightness and correspond to the plurality of reference images; and a brightness correction unit configured to correct a brightness of an input pixel on the basis of reference shading data that is selected among the reference shading data depending on the brightness of the input pixel, and brightness information on a target block that is selected among the blocked brightness information of the selected reference shading data depending on coordinates of the input pixel, wherein the reference image is divided into reference image blocks, wherein the reference shading data includes brightness information comprising representative brightness values of the divided reference image blocks, wherein a piece of reference shading data corresponding to a reference image having a minimal average brightness is selected when the brightness of the input pixel is equal or less than the minimal average brightness, and a piece of reference shading data corresponding to a reference image having a maximal average brightness is selected when the brightness of the input pixel is equal or greater than the maximal average brightness, wherein brightness weights of four corner parts of a target block are determined by dividing a maximal representative brightness value among representative brightness values of reference image blocks comprised in the selected piece of reference shading data by brightness values of the four corner parts of the target block, wherein a brightness weight of the input pixel is determined by processing the brightness weights of the four corner parts by two-dimensional linear interpolation, and wherein the brightness of the input pixel is corrected by multiplying the brightness of the input pixel by the brightness weight of the input pixel.