1. A method for identifying halftone regions, comprising: performing by a computer: receiving a region from a digital image, wherein the digital image is a bi-level image, wherein each pixel has two possible color values; computing a variation index for the region, wherein the variation index indicates how frequently adjacent pixel values in the region differ; in response to determining that the variation index for the region is between an upper threshold and a lower threshold, determining whether the variation index is above a middle threshold and the region contains black patches, wherein the variation index being greater than the upper threshold is indicative of the region being a halftone region and the variation index being less than the lower threshold is indicative of the region being a non-halftone region; and in response to determining that the variation index is above a middle threshold and that the region contains black patches, determining that the region is a halftone region.