Massimiliano Corsini

Wavelet-based blind watermarking of 3D models

Watermarking of 3D meshes has received a limited attention due to the difficulties encountered in extending the algorithms developed for 1D (audio) and 2D (images and video) signals to topological complex objects such as meshes. Other difficulties arise from the wide variety of attacks and manipulations 3D watermarks should be robust to. For this reason, most of the 3D watermarking algorithms proposed so far adopt a non-blind detection. In this paper we present a new blind watermarking algorithm for 3D meshes. In order to simultaneously achieve watermark imperceptibility and robustness a multiresolution framework is adopted. To do so we assume that host meshes are semi-regular ones, a property that permits to first perform a wavelet decomposition and then to embed the watermark at a suitable resolution level. Watermark detection is accomplished by computing the correlation between the watermark signal and the to-be-inspected mesh. Robustness against geometric transformations such as rotation, translation and uniform scaling is achieved by embedding the watermark in a normalized version of the host mesh, obtained by means of Principal Component Analysis. Experimental results show the validity of the proposed algorithm both in terms of imperceptibility and robustness against a wide class of attacks including noise addition, smoothing and cropping.

Watermarked 3-D Mesh Quality Assessment

This paper addresses the problem of assessing distortions produced by watermarking 3D meshes. In particular, a new methodology for subjective evaluation of the quality of 3D objects is proposed and implemented. Two objective metrics derived from measures of surface roughness are then proposed and their efficiency to predict the perceptual impact of 3D watermarking is assessed and compared with the state of the art. Results obtained show good correlations between the proposed objective metrics and subjective assessments by human observers

Objective evaluation of the perceptual quality of 3D watermarking

In this paper an objective metric to measure the perceptual quality of watermarked 3D meshes is presented. The metric, which is based on a black-box approach, relies on the measurement of the roughness of 3D meshes before and after the insertion of the watermark. To calibrate the metric and to validate it, a set of psychovisual experiments has been carried out. Due to the lack of prior work in this field, a new methodology for the subjective evaluation of the quality of watermarked 3D objects is introduced. The validity of the proposed metric has been tested against a number of different 3D watermarking algorithms, showing an excellent match with the subjective evaluation of the quality stemming from the psychovisual experiments.

ArtShop: an art‐oriented image‐processing tool for cultural heritage applications

Advances in electronic imaging over recent years have encouraged the development of newtools for cultural heritage applications. In this paper a software application called ArtShopis described, containing some tools for artwork image restoration, developed during severalyears of research at the Image and Communications Laboratory of the University ofFlorence. Copyright # 2003 John Wiley & Sons, Ltd.Received: 10 January 2003; Revised: 19 March 2003

Towards 3D watermarking technology

In the last years the applications using and managing 3D data are quickly increasing: archaeological site reproduction, virtual museums (in the field of Cultural Heritage); games, animations, special effects (in the field of entertainment); enhanced user navigation, e-commerce, virtual reality (in Internet) are only some examples of the potentialities of such data. In this evolving scenario the demand for IPR protection of this kind of multimedia data is growing and new interest is moving towards 3D watermarking. This paper discusses some issues on 3D watermarking, such as robustness and visual quality, and presents a panoramic on some 3D watermarking models proposed so far. Regarding the visual quality aspect, a novel solution to reduce the perceptibility of the watermark, embedded through vertices perturbations is proposed.

ArtShop: a tool for art image processing

The progress of electronic imaging has encouraged the development of new tools for cultural heritage applications. In this paper some software, ArtShop, is described that contains tools for artwork image restoration, developed over several years of research.

Digital watermarking of 3D meshes

Despite the increasing interest in digital watermarking of multimedia data, watermarking of 3D geometrical models has received little attention by the research community. One of the main reasons is that geometric data is intrinsically complex to handle, in addition a lot of diverse attacks can be thought of that are not possible in the 2D and 1D cases. So it is very difficult to develop robust watermarking algorithms for 3D models. In order to overcome the above problems most of the systems proposed so far exploit the knowledge of the original, non marked, mesh for watermark recovery. The practical usefulness of non-blind schemes, though, is very limited, hence the need to develop new blind schemes for 3D watermarking. In this paper we propose a blind watermarking algorithm for 3D meshes. Watermarking is achieved by perturbing the position of the vertices of the model according to a spherical pseudo-random bumped surface. The pseudo-random position and amplitude of the bumps encode the watermark. In order to gain robustness while keeping the distortion to a minimum, the watermark is embedded into a low resolution version of the mesh. The coarse version of the model is obtained by a MAPS1 (Multiresolution Adaptive Parameterization of Surface) algorithm. The base domain produced by this algorithm is used to obtain the full resolution watermarked model from the coarse watermarked one. Watermark recovery is accomplished by means of a standard correlation detector. Experimental results show that the system assure high visual quality of the watermarked model, and that a good degree of robustness can be reached for models with a suffciently high number of faces.

Mosaicing for high resolution acquisition of paintings

There is an every day increasing interest toward the applications of image processing techniques to the field of Cultural Heritage, the main objectives being high quality archival, image reproductions enhancement, virtual reconstruction, virtual restoration. This paper deals with the problem of setting up a simple and automatic procedure for obtaining a high resolution picture of a painting starting from a set of overlapped images showing different parts of the painting itself. With respect to other mosaicing techniques the proposed method allows to compose the whole picture even in the presence of strong colour distortions. This is possible thanks to the use of an ordinal measure as a similarity criterion for evaluating the correspondences between the images. Experimental results have demonstrated the good performances of the proposed method.

Research of the Image Processing and Communications Lab. of the University of Florence in the cultural heritage field

The goal of this paper is to present the research that has been carried out over the last 10 years in the Image Processing and Communications Lab of the University of Florence for developing applications for the cultural heritage field. In particular research has focused on the following issues: high resolution acquisition of paintings by means of mosaicing techniques, colour calibration of the acquisition devices, tools for forecasting the results of restoration processes (in particular with reference to the cleaning process), systems for producing virtually restored digital copies of paintings (in particular for filling in cracks and lacunas). The problems related to the distribution of the digital copies have also been considered, in particular with reference to the watermarking of the images for copyright protection. The methodologies developed by the Lab with reference to the above mentioned issues will be described, and the main results discussed.