Print-Scan Resilient Watermarking for the Chinese Text Image

Digital text watermarking has been a popular way to discourage illicit reproduction of documents by embedding copyright information into them. This study presents two robust watermarking algorithms for the Chinese text image. One embeds watermark by modulating the character spacings and the other is based on the relative heights of characters in the same text line. In the embedding process, the characters are segmented firstly by projecting the image horizontally and then vertically. And the rough segmentation is refined according to the peculiarity of Chinese characters. Then on the basis of character segmentation algorithm, watermark embedding is achieved by shifting characters up or down (left or right). In the extracting process, pre-process operations such as the binarization and image deskewing algorithm are done first to reduce the impact caused by print-scan operation. Then the messages are extracted by comparing the character spacings or relative heights of characters. Experimental results show that the proposed methods possess high extraction accuracy under the tampering of print-scan operations.