3-D images transmission in a way which is compliant with traditional 2-D representations can be done through the embedding of disparity maps within the 2-D signal. This approach enables the transmission of stereoscopic video sequences or images on traditional analogue TV channels (PAL or NTSC) or printed photographic images. The aim of this work is to study the achievable performances of such a technique. The embedding of disparity maps has to be seen as a global rate-distortion problem. The embedding capacity through steganography is determined by the transmission channel noise and by the bearable distortion on the watermarked image. The distortion of the 3-D image displayed as two stereo views depends on the rate allocated to the complementary information required to build those two views from one reference 2-D image. Results from the works on the scalar Costa scheme are used to optimize the embedding of the disparity map compressed bit stream into the reference image. A method for computing the optimal trade off between the disparity map distortion and embedding distortion as a function of the channel impairments is proposed. The goal is to get a similar distortion on the left (the reference image) and the right (the disparity compensated image) images. We show that in typical situations the embedding of 2 bits/pixels in the left image, while the disparity map is compressed at 1 bit per pixel leads to a good trade-off. The disparity map is encoded with a strong error correcting code, including synchronisation bits.
The resistance of watermarking schemes against geometrical distortions has been the subject of quite much research in the last ten years. The ability for a communication scheme to cope with a loss of synchronization is indeed a very difficult issue. Still, the tolerance of the human visual perception in presence of such distortions is surprisingly high and situations where loss of synchronization takes place are numerous. The aim of this paper is to present an extensive survey of existing works addressing this particular problem. Each of the proposed class of techniques will be analyzed to show which forms and what severity of distortions it is able to survive. The possible security implications of the proposed techniques will also be studied. We will try to point out the strengths and weaknesses of each solution. Special attention will be given to implementation details such as cropping operation which is subsequent to most geometrical distortions. Partial loss of content, change of width to height ratio or modification of the image size have important consequence on some proposed schemes. We will also briefly discuss the difficulty to evaluate the severity of a geometrical distortion.
One of the most active research area in the watermarking community is the research in dealing with geometric distortion. The geometric distortion problem has two aspects, namely its effect on watermark detectability and its effect on the perceptual quality of the watermarked data. Most research in this area has been concentrated on addressing the first aspect of the problem, and research on objective visual quality assessment of geometrically distorted images is not widely discussed in the literature. As a consequence, there is a lack of objective visual quality measurement for this class of distortion. In this paper we propose a method of objectively assessing the perceptual quality of geometrically distorted images. Our approach is based on the modeling of a complex, global geometric distortion using local, simpler geometric transformation models. The locality of this simpler geometric transformation determines the visual quality of the distorted images.
Many watermarking applications may benefit from the availability of both the original and the watermarked media content to perform detection. However, one must take into account that the watermarked media might have undergone deformations such that direct correspondence between original and watermarked signal is not possible anymore. Extra processing is therefore needed to benefit from the availability of both signals. In video applications, besides the spatial deformations, one must also consider a possible temporal structure modification of the watermarked content. Such distortions include frame rate modifications, scene removal and temporal cropping. In this paper, we present how one can perform an automatic frames alignment of spatially and temporally deformed video sequences. Our approach consist in establishing a correspondence between automatically detected key-frames in the two sequences. The key-frame detection is inspired from existing methods dealing with scene cuts localization and semantics (MPEG7-like) scene classification. Different simulations show that the method can cope with common temporal deformations.
A challenging aspect in the development of robust watermarking algorithms is the ability to withstand complex geometric distortion of the media. A few existing techniques are known to deal with such transformations up to a certain level. Traditionally, the measure of the degradation caused by an attack on an image only addressed the pixel value modification. However, a degradation consequent to the geometric distortion of an image cannot be measured with traditional criteria. Therefore the evaluation and comparison of the robustness to desynchronization of different watermarking schemes was not possible. In this paper, we present an innovative method to measure the distortion introduced by complex geometric deformations of an image. The distortion measure is expressed in term of how closely the applied transform can be approximated by a simpler transform model (e.g. RST transform, affine transform). The scheme relies on the local least square estimation of the parameters of the reference transform model. Eventually, we illustrate the proposed measure by presenting some results for different complex image distortions.
As concern about watermark robustness grows, different approaches based on the introduction of synchronization marks have been presented to survive geometrical attacks. Most of the proposed techniques rely either on the introduction of a dedicated template either on the detection of particular properties in the autocorrelation function (ACF) of the watermark itself in order to resist against scaling and rotation transformations. The use of this side-information at the detector makes an inversion of the transformation possible. However, due to the publicness of this side-information, those techniques turn out to be very vulnerable to a removal attack. We propose an innovative method to hide the synchronization marks and therefore prevent malicious removal attacks (eg. template attack,...). The ability to detect the synchronization marks will be conditioned by the knowledge of a secret key. The technique consists in using an image dependent secret binary mask to modulate the synchronization pattern before it is introduced in the image. The ability to recover this binary mask upon rotation and scaling allows the detection of the synchronization marks even after transformation. Although mask recovering presents a considerable error rate, sufficient detection of the synchronization marks can be achieved. The mask, obtained from a signal-dependent partition, leads to a spectral spreading of the synchronisation mark, making template attacks nearly impossible to perform.
This paper describes the functional model of a combined conditional access and fingerprinting copyright (-or projectionright) protection system in a digital cinema framework. In the cinema industry, a large part of early movie piracy comes from copies made in the theater itself with a camera. The evolution towards digital cinema broadcast enables watermark based fingerprinting protection systems. Besides an appropriate fingerprinting technology, a number of well defined security/cryptographic tools are integrated in order to guaranty the integrity of the whole system. The requirements are two-fold: On one side, we must ensure that the media content is only accessible at exhibition time (under specific authorization obtained after an ad-hoc film rental agreement) and contains the related exhibition fingerprint. At the other end, we must prove our ability to retrieve the fingerprint information from an illegal copy of the media.
In this paper, we investigate the restoration of geometrically altered digital images with the aim of recovering an embedded watermark information. More precisely, we focus on the distorsion taking place by the camera acquisition of an image. Indeed, in the cinema industry, a large part of early movie piracy comes from copies made in the theater itself with a camera. The evolution towards digital cinema broadcast enables watermark based fingerprinting protection systems. The first step for fingerprint extraction of a counterfeit material is the compensation of the geometrical deformation inherent to the acquisition process. In order to compensate the deformations, we use a modified 12-parameters bilinear transformation model which closely matches the deformations taking place by an analog acquisition process. The estimation of the parameters can either be global, either vary across regions within the image. Our approach consist in the estimation of the displacement of a number of of pixels via a modified block-matching technique followed by a minimum mean square error optimization of the parameters on basis of those estimated displacement-vectors. The estimated transformation is applied to the candidate image to get a reconstruction as close as possible to the original image. Classical watermark extraction procedure can follow.