Patent ID: 8792139

Claim:
A method for correcting an image used by an image processing apparatus that corrects a shadow in a bound portion included in document image data obtained by reading a bound document, the method comprising the steps of: extracting shadow image data including a region of the shadow from the document image data; generating, for the shadow image data by determining intervals between grid lines, a grid with which a ratio of changes in luminance between the grid lines in directions that are perpendicular to each other is proportional to a median of ratios of changes in luminance between grid lines in directions that are perpendicular to each other for a first plurality of grids comprising the shadow image data, and that has a number of grid points that can be stored in a capacity of a memory for correction values; calculating first correction values that correct luminance of pixels in the shadow image data corresponding to grid points of the grid; storing the first correction values in the memory; calculating second correction values for luminance of the pixels in the shadow image data based on the first correction values of grid points that are close to a position of each pixel, the first correction values being read from the memory; and correcting luminance of the document image data using the first correction values and the second correction values.