1. An apparatus for analyzing a histogram of an image, the apparatus comprising: an image input module for buffering an input image; a block calculator for: performing a blocking operation for dividing the image, which has been input to the image input module, into pixel blocks of a predetermined size, and extracting and outputting a representative pixel of each block obtained by corresponding blocking, wherein the representative pixel is selected as at least one of the pixels in an associated pixel block; a probability density function (PDF) operator for: calculating a first histogram by using all pixels of the image, which has been input to the image input module, and calculating a second histogram of the image by using the representative pixels input from the block calculator, said representative pixels being associated with corresponding pixels blocks; and an image characteristic comparator for: receiving the first and second histograms output from the PDF operator, testing if the received histograms satisfy a predetermined identity criterion by comparing characteristics of the first histogram with characteristics of the second histogram, and calculating a third histogram of a following input image based on representative pixel values of the following image associated with a block size obtained as a result of satisfying the predetermined identity criterion.