Document image binarization method based on content type separation

摘要

A method for binarizing a grayscale document image, which first divides the document image into a plurality of sub-images and determining a type of each sub-image based on a horizontal projection profile and a density of each sub-image, the type being 1: text only, 2: graphics only, 3: photo only, 4: text and graphics, 5: text and photo, 6: graphics and photo, or 7: text and graphics and photo. Then a selected one of first to seventh binarization processes is applied to binarize each sub-image based on its type to generate a binary sub-image. All binary sub-images are then combine to generate a binary image of the grayscale document image. Of the first to seventh binarization processes respectively applied to the first to seventh types of sub-images, at least those for the first, second, third, fifth, sixth and seventh type are different from each other.