Watermark embedding in halftoned images

摘要

A method of processing a continuous tone image includes using a halftone screen to generate a bi-level bitmap (310); partitioning the contone image into an array of image blocks (315); halftoning the image blocks (340); using the bi-level bitmap to select some of the halftone image blocks (350); and modifying the selected halftone image blocks using code words (350), such that information contained in the code words is embedded in a halftone image (390). A method of extracting embedded information in a halftone image includes accessing a bi-level bit map (450); partitioning the halftone image into a plurality of image blocks (400); using the bitmap to select at least some of the blocks (430); identifying a code word sequence in the selected blocks (440); and extracting the information from the code word sequence (480).