Robust Watermarking of Cartographic Images
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obust Watermarking of Cartographic Images Mauro Barni Department of Information Engineering, University of Siena, Via Roma 56, 53100-Siena, Italy Email: [email protected]
Franco Bartolini Department of Electronics and Telecommunications, University of Florence, Via S. Marta 3, 50139-Firenze, Italy Email: [email protected]fi.it
Alessandro Piva Department of Electronics and Telecommunications, University of Florence, Via S. Marta 3, 50139-Firenze, Italy Email: [email protected]fi.it
Filippo Salucco Department of Electronics and Telecommunications, University of Florence, Via S. Marta 3, 50139-Firenze, Italy Email: [email protected]fi.it Received 30 April 2001 and in revised form 15 October 2001 We present a method (Text-Based Geometric Normalization—TBGN) which, by exploiting the particular content of cartographic images, namely text content, permits to cope with global geometric transformations. First, text is extracted from the to-be-marked map, then text orientation and size are exploited to normalize the image geometry prior to watermark insertion. Watermarking is performed by means of any of the existing algorithms ensuring good robustness against image processing tools. At the decoder side, text is extracted again from the map and used to normalize image geometry. Owing to the robustness of text features with respect to common image manipulations, and to the likely spreading of text all across the digital map, the proposed system exhibits an excellent robustness. Keywords and phrases: digital watermarking, map watermarking, robust watermarking, geometric normalization.
1. INTRODUCTION Image watermarking has been widely studied in the last years for its importance in copyright protection applications involving the exchange of visual data in digital format. At the beginning, the exchange of general purpose data was considered without taking into account the peculiarities of the image data to be protected. Such an approach has lead to the development of a wide variety of general image watermarking algorithms which can be used virtually in any application environment [1]. As research has gone on, the necessity of applying digital watermarking in more restricted scenarios has come out, thus calling for the development of ad hoc watermarking solutions capable of coping with and exploiting the peculiarities of the application at hand. Possible examples include the watermarking of video surveillance data [2, 3], medical images [4], cartoons [5], and remote sensing imagery [6]. From a general point of view, the necessity of dealing with a class of images having peculiar characteristics has two main
consequences. From one side, the invisibility requirement must be carefully revised, since it may assume a completely different meaning with respect to conventional multimedia applications. From the other side, image peculiarities may be used to develop ad hoc solutions to problems which are hard to solve when looked at from a general perspective. This is the case, for example, of video surveillance data authentication, whe
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