Digital Watermarking Method to Extract Watermarks from Printed Matters with Cell Phone by Using Finder Patterns and Alignment Pattern of QR Code

摘要

There are some watermarking methods to be ableto extract a watermark even from a printed watermarked image with cell phones. In such a use, the speed of extracting watermark should be fast for users' convenience, where QR codes are used for the similar purpose. However, QR codes require its own space in addition to contents and its appearance of QR codes is unattractive. On the other hand, digital watermarking requires no additional space, and its appearance is visually attractive. Nakamura's method used a black frame for identifying a watermarked area. The problem of Nakamura's method is a large constraint on original images and inconvenient extraction way. Therefore, we employ the finder pattern and the alignment pattern of QR codes for position detection. The advantage of the proposed method is a small constraint on design and convenient way of real time extraction. In the experiment, we implement the proposed method as an Android application and evaluate its performance including its real extraction time on a cell phone. The experimental results confirm that the proposed method can extract a correct watermark in 2 seconds, where it is enough fast in practice.