1. An image processing method comprising: dividing an image into at least one region; obtaining a region-based histogram smoothing function for processing the image to have a uniform number of pixels based on a pixel value for each region of of the divided image; obtaining a global smoothing function for an entire region of the image by using the obtained region-based histogram smoothing function of each region in the divided image; obtaining a local smoothing function for each pixel in the image by using the region-based histogram smoothing function which is applied to a region included in a block; determining a sum of weight values of the global smoothing function and the local smoothing function; and determining the pixel value for said each region of the divided image, based on the determined sum of the weight values.