Séverine Baudry

Virtual view invariant domain for 3D video blind watermarking

3D video content has been receiving increasing interest over the last few months and created challenges regarding how to protect such high valued items. For instance, depth-image-based rendering techniques allowing for the creation of virtual views may impair underlying watermarks embedded within individual views. In contrast with previous works, this article focus on defining a view-independent watermark embedding domain rather than a watermarking system coherent with the disparity across several views, thus permitting blind detection. More specifically, based on the fact that pixel displacements across views most often reduce to horizontal shifts, the average luminance value along the rows of the video frames have been selected for watermark embedding. Experimental results clearly prove the robustness of the watermark against virtual views generation.

Frame-accurate temporal registration for non-blind video watermarking

Non-blind watermark detection is still relevant in some applications e.g. traitor tracing. In this case, the auxiliary metadata sent to the detector reveals something about the original content. In this paper, we investigate whether such side-information could also be exploited for registration purpose.n To this end, we take a reference non-blind video watermarking system for H.264 AVC CABAC video and show that the watermark auxiliary information could be used in a fingerprint-based registration framework. Our proposed registration strategy operates in two steps: first, identify in the candidate video the best match for each watermarked frame of the master video ; second, discard frames which are most likely to be misregistered (for instance, watermarked frames which have been deleted in the candidate video).n In comparison with conventional fingerprint-based techniques, the advantage of this strategy is twofold: (i) the accuracy of the registration naturally adapts to the watermark information density carried by each frame and (ii) it does not require additional storage overhead. Reported experimental results clearly demonstrate that the proposed registration approach largely outperforms other ones relying on independent video fingerprints.

A sneak peek into the camcorder path

A number of technologies claim to be robust against content re-acquisition with a camera recorder e.g. water- marking and content ngerprinting. However, the benchmarking campaigns required to evaluate the impact of the camcorder path are tedious and such evaluation is routinely overlooked in practice. Due to the interaction between numerous devices, camcording displayed content modi es the video essence in various ways, including geometric distortions, temporal transforms, non-uniform and varying luminance transformations, saturation, color alteration, etc. It is necessary to clearly understand the di erent phenomena at stake in order to design ef- cient countermeasures or to build accurate simulators which mimic these e ects. As a rst step in this direction, we focus in this study solely on luminance transforms. In particular, we investigate three di erent alterations, namely: (i) the spatial non uniformity, (ii) the steady state luminance response, and (iii) the transient luminance response.

Flicker Forensics for Pirate Device Identification

Cryptography-based content protection is an efficient means to protect multimedia content during transport. Nevertheless, content is eventually decrypted at rendering time, leaving it vulnerable to piracy e.g. using a camcorder to record movies displayed on an LCD screen. Such type of piracy naturally imprints a visible flicker signal in the pirate video due to the interplay between the rendering and acquisition devices. The parameters of such flicker are inherently tied to the characteristics of the pirate devices such as the back-light of the LCD screen and the read-out time of the camcorder. In this article, we introduce a forensic methodology to estimate such parameters by analyzing the flicker signal present in pirate recordings. Experimental results clearly showcase that the accuracy of these estimation techniques offers efficient means to tell-tale which devices have been used for piracy thanks to the variety of factory settings used by consumer electronics manufacturers.

Modeling the flicker effect in camcorded videos to improve watermark robustness

Camcording a screen is a common and easy way for a pirate to capture a protected video and circumvent any cryptography-based protection system like DRM. Therefore, antipiracy methods like watermarking should be robust to this type of attack. One effect very often encountered is the flicker effect: image luminance varies periodically along the video, and scrolling stripes may also be observed. Such an effect is due to aliasing, because the higher frequency backlight of the screen is sampled at a lower rate by the camcorder. The stripe effect appears because each line of the image is captured with a small delay with CMOS sensors. We show that the amplitude of the flicker depends on the luminance of the displayed image, as well as on the luminosity of the screen and on the exposure setting of the camcorder. We propose a method to blindly estimate the flicker parameters by studying the spectrum of the camcorded video; then we show how the flicker can be selectively removed without impairing other frequential components of the video. Experiments on camcorded videos show that removing the flicker enable significant improvement in the watermarking detection performances.

Forensic characterization of pirated movies: digital cinema cam vs. optical disc rip

A large portion of pirate movies illegally shared over the Internet is either a camcorded copy of a projection in a digital cinema or is directly ripped from optical discs such as DVDs and Blu-ray discs. In this paper, we introduce a classifier that automatically discriminates between these two types of piracy in an effort to provide tools that help streamlining the whole forensic analysis process. This oracle relies on tell-tale visual artifacts that reveal the occurrence of camcording. We survey three alternate discriminative features relating to temporal flicker, color gamut, and edge orientation and detail how to combine them to obtain accurate classification. Experiments conducted on a large corpus of real pirated movies clearly demonstrate the feasibility of such classification.

Blind detection for disparity-coherent stereo video watermarking

Stereo video content calls for new watermarking strategies, e.g. to achieve robustness against virtual view synthesis. Prior works focused either on inserting the watermark in an invariant domain or on guaranteeing that the watermarks introduced in the left and right views are coherent with the disparity of the scene. However, the first approach raises fidelity issues while the second requires side information at detection i.e. the detector is not blind. In this paper, we propose a new blind detection procedure for disparity-coherent watermarks. In a nutshell, the detector relies on cross-correlation to aggregate the scattered pieces of the embedded reference watermark pattern rather than warping the reference pattern according to the parameters of the current view prior to detection. Reported experimental results indicate that this revisited detector successfully manages to retrieve embedded watermarks even after lossy compression.

Exploring color information to characterize camcorder piracy

Nowadays, forensic watermarks are introduced at projection time in movie theater. This provides the Entertainment industry with a tracing mechanism to identify indelicate cinema owners, who would have let camcorders enter their premises. However, the watermarking technologies deployed in film-based theaters and digital cinemas differ. For cost efficiency during forensic analysis, it is desirable to have a reliable oracle that can accurately discriminate between film and digital projection recordings. Prior work focused on tell-tale artifacts present in the luminance channel to build a classifier. In this paper, we investigate whether color information could also be exploited. We introduce a number of features that relate either to color saturation or color bias, and assess their discriminative power in a systematic fashion. Experimental results on a data set containing nearly 250 real-life full length camcorded movies suggest that the color bias seems to provide the highest classification potential.

Disparity estimation and disparity-coherent watermarking

In the context of stereo video, disparity-coherent watermarking has been introduced to provide superior robustness against virtual view synthesis, as well as to improve perceived fidelity. Still, a number of practical considerations have been overlooked and in particular the role of the underlying depth estimation tool on performances. In this article, we explore the interplay between various stereo video processing primitives and highlight a few take away lessons that should be accounted for to improve performances of future disparity-coherent watermarking systems. In particular, we highlight how lost correspondences during the stereo warping process impact watermark detection, thereby calling for innovative designs.

Flicker Forensics for Camcorder Piracy

Camcorder piracy refers to the process of using a camcorder to record a screen that displays copyrighted content. In contrast to the previous works that aimed at detecting the occurrence of camcorder piracy, this paper conducts an in-depth study of the luminance flicker that is naturally present in camcorded videos due to the interplay between a liquid-crystal-display (LCD) screen and a camcorder. We first model the flicker signal and show that its parameters are tied to such internal characteristics of the pirate devices as the back-light frequency of the LCD screen and the read-out time of the camcorder. We then present new estimation techniques to recover these hidden parameters directly from camcorded videos and demonstrate that such forensic cues could provide intelligence on the pirate devices. We also discuss how to recover the shape of the low-power flicker signal itself and show that it could be used to infer which back-light technology employed in the pirate LCD screen.