Patent ID: 8311326

Claim:
An image processing system comprising: a histogram preparer configured to read in order a set of image data scanned from an original by a prescribed unit of reading thereof, and prepare a histogram representing pixel numbers of densities of image data of an N-th region of pixels scanned from the original, where N is an integer variable up to a maximum number of a total number of regions for reading; a background density estimator configured to estimate a background density of the original as a density corresponding to a local maximal value in view of a highlight end of the histogram as prepared; a background removal reference value setter configured to set up a background removal reference value based on a pixel number corresponding to the background density as estimated; a background removal threshold determiner configured to set up an N-th provisional background removal threshold as a sum of the background density as estimated and the background removal reference value as set up, and determine a background removal threshold of image data of the N-th read pixel region based on the N-th provisional background removal threshold and a background removal threshold of image data of an (N−1)-th read pixel region; and a background remover configured to remove a background of image data of the N-th read pixel region based on the background removal threshold of image data of the N-th read pixel region, wherein the background density estimator is configured to estimate the background density of the original as a background density based on a local maximal value in view of a highlight end of a smoothed histogram of the histogram as prepared and exceeding at least one threshold of pixel number in view of the highlight end of the smoothed histogram, and wherein the background density estimator has a first threshold of pixel number set to a first range of background densities close to the highlight end of the smoothed histogram, and a second threshold of pixel number smaller than the first threshold of pixel number set to a second range of background densities distant from the highlight end of the smoothed histogram.