directions, of the magnitude of the level-3 coefficients and construct a 2D array. .... pirates thwarted in attempt to camcord Mission Impossible: III in Los. Angeles ...
P2-25
A Novel Blind Video Watermarking Scheme for Access Control Using Complex Wavelets Mark PICKERING, Lino E. CORIA, and Panos NASIOPOULOS
Abstract-- A content-dependent watermarking scheme for access control of digital video is presented. The watermark is embedded in selected complex wavelet coefficients of every frame. Robustness to geometric attacks is guaranteed since complex wavelets provide shift invariance and good directional selectivity.
I. INTRODUCTION Over 90% of initial film releases that are pirated are a result of camcording in movie theaters [1]. To alleviate this problem, Digital Rights Management (DRM) systems rely on watermarking in a variety of ways [2], [3]. One example is access control where a watermark embedded in the video sequence provides information on whether video players are authorized to reproduce the content or not. In practice, a watermark would be embedded in the copy of the movie released for display in cinemas. Since the watermark is embedded in the content of the movie, a pirated copy produced by a camcorder will still contain the watermark. Then if the pirated copy is played in a compliant DVD player, the player will detect the watermark and deny access to the content. We present a new method that employs the Dual-Tree Complex Wavelet Transform (DT CWT) developed in [4] to embed a watermark in high textured areas of the video frames. Complex wavelets can provide both shift invariance and good directional selectivity, with only a modest increase in signal redundancy and computational load. This feature is used to achieve robustness to geometric attacks.
II. PROPOSED METHOD The watermark is a vector of length six whose elements are I's and -I's (e.g. [1 -1 1 -1 1 -1]). To make the watermark difficult to detect by an attacker, we pseudo-randomly reorder its elements by utilizing a key K that is only known to the encoder and decoder. We call this reordered vector w, and this is the watermark that will be embedded in the video frames. For each frame, a four-level DT CWT is applied in order to find the coefficients. We then find the minimum, across all six directions, of the magnitude of the level-3 coefficients and construct a 2D array. We apply a low-pass filter to this array and sub-sample by a factor of 2 in each direction to create the array p(U4, V4) with the same dimensions as the level-4 subbands. We now find the values in p(U4, V4) which exceed an embedding threshold, x. The re-ordered watermark, w, will be added to the magnitudes of the level-4 coefficients at these locations and in all six directions in the following manner: This work was partially supported by CONACyT and ITESO (Mexico).
1-4244-0763-X/07/$20.00 ©2007 IEEE
m4,d (U4, V4 )
m4,d (U4,V4)+aWdp(U4,V4)
1m4,d (U4,V4)
otherwise
ford= 1, ..., 6. In this equation, Wd is the dth element of vector w. The scaling factor ais a positive number that is used along with the value of p(U4, V4) to control the strength of the embedded watermark. This parameter a is obtained in the following way: a= Rd I np. Rd iS the desired robustness strength that we wish to achieve on every frame, whereas np represents the number of values from p(U4, V4) that are greater than r. A final restriction is imposed on a so that it does not become too small or too large: if a< amin then a= amin if a> amam then a= amam where a°rin and ax are constants, and amin < amax
Encoder (a)
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Firid Locations to DPetect
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EF
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Undo Reordng of
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