Patrick Gioia

Subdivision surfaces in MPEG-4

SS (subdivision surfaces) are a powerful modelling paradigm for truly hierarchical (instead of merely progressive) 3D surface (as opposed to mesh) coding. Two SS-based tools of the MPEG-4 animation framework extension allow us to derive a piecewise smooth surface from an initial control mesh: if the subdivision process is run in its predefined form, the initial mesh is simply smoothed; if 3D details are added to the positions of the new vertices appearing after each subdivision step, a particular target surface may be approximated with an increasing accuracy. In both cases, multiresolution editing/animation is possible.

Peer-to-peer visualization of very large 3D landscape and city models using MPEG-4

The recent availability of broadband Internet access and web-based visualization techniques is paving the way for a large scale use of 3D landscape and city models for a great variety of professional and mass market services. To make such services appealing to a large audience, these 3D models must reach a sufficient level of realism and accuracy. Many solutions are now available to automatically generate 3D models of huge urban environments. Geographic Information System (GIS) databases (i.e. terrain elevation grids, ortho photographs, buildings footprint and height) provide a good basis for generating such models at affordable cost with minimum human intervention. However, the growing size of the transmitted data will favour streaming over download-and- play. Moreover, the new market for virtual worlds is likely to be soon demanding in interoperability. The goal of this paper is to show how solutions based on hierarchical LOD models and view-dependent progressive streaming can efficiently be implemented using the MPEG-4 AFX standard in peer-to-peer networks architectures, solving both streaming and interoperability issues.

Peer-to-Peer Visualization of Very Large 3D Landscape and City Models Using MPEG-4

The recent availability of broadband Internet access and web-based visualization techniques is paving the way for a large scale use of 3D landscape and city models for a great variety of professional and mass market services. To make such services appealing to a large audience, these 3D models must reach a sufficient level of realism and accuracy. Many solutions are now available to automatically generate 3D models of huge urban environments. Geographic Information System (GIS) databases (i.e. terrain elevation grids, ortho photographs, buildings footprint and height) provide a good basis for generating such models at affordable cost with minimum human intervention. However, the growing size of the transmitted data will favour streaming over download-and- play. Moreover, the new market for virtual worlds is likely to be soon demanding in interoperability. The goal of this paper is to show how solutions based on hierarchical LOD models and view-dependent progressive streaming can efficiently be implemented using the MPEG-4 AFX standard in peer-to-peer networks architectures, solving both streaming and interoperability issues.

Hybrid approach for fast occlusion processing in computer-generated hologram calculation

A hybrid approach for fast occlusion processing in computer-generated hologram calculation is studied in this paper. The proposed method is based on the combination of two commonly used approaches that complement one another: the point-source and wave-field approaches. By using these two approaches together, the proposed method thus takes advantage of both of them. In this method, the 3D scene is first sliced into several depth layers parallel to the hologram plane. Light scattered by the scene is then propagated and shielded from one layer to another using either a point-source or a wave-field approach according to a threshold criterion on the number of points within the layer. Finally, the hologram is obtained by computing the propagation of light from the nearest layer to the hologram plane. Experimental results reveal that the proposed method does not produce any visible artifact and outperforms both the point-source and wave-field approaches.

Computer generated hologram from Multiview-plus-Depth data considering specular reflections

A novel approach for hologram computation from Multiview-plus-Depth (MVD) data is studied in this paper. The proposed method consists of three steps. First, intensity views and depth maps pairs of the scene are taken from different perspective viewpoints. Then, the 3D scene geometry is reconstructed from the MVD data as a layered point-cloud. This 3D scene reconstruction step allows us to use only a few perspective projections of the scene without sacrificing any depth cue. Furthermore, in order to take into account specular reflections, each scene point is considered to emit light differently in all the directions. Finally, light scattered by the scene is numerically propagated towards the hologram plane in order to get the final CGH. Experimental results show that the proposed method is able to provide all the human depth cues and accurate shading of the scene without producing any visible artifact.

Complex modulation computer-generated hologram by a fast hybrid point-source/wave-field approach

We propose a fast Computer-Generated Hologram (CGH) computation method based on a hybrid point-source/wave-field approach. Whereas previously proposed methods tried to reduce the computational complexity of the point-source or the wave-field approaches independently, our method uses the two approaches together and therefore takes advantages from both of them. The algorithm consists of three steps. First, the 3D scene is sliced into several depth layers parallel to the hologram plane. Then, for each layer, we compute the complex wave scattered by this layer either using a wave-field or a point-source approach according to a threshold criterion on the number of points within the layer. Finally, we sum up the complex waves scattered by all the depth layers in order to obtain the final CGH. Experimental results reveal that this combination of approaches does not produce any visible artifact and outperforms both the point-source and wave-field approaches.

View-dependent compression of digital hologram based on matching pursuit

In this paper we investigate the suitability of Gabor Wavelets for an adaptive partial reconstruction of holograms based on the viewer position. Matching Pursuit is used for a sparse light rays decomposition of holographic patterns. At the decoding stage, sub-holograms are generated by selecting the diffracted rays corresponding to a specific area of visualization. The use of sub-holograms has been suggested in the literature as an alternative to full compression, by degrading a hologram with respect to the directional degrees of freedom. We present our approach in a complete framework for color digital holograms compression and explain, in details, how it can be efficiently exploited in the context of holographic Head-Mounted Displays. Among other aspects, encoding, adaptive reconstruction and selective degradation are studied.

Complex Modulation Computer-Generated Hologram with Occlusion Effect by a Fast Hybrid Point-source/Wave-field Approach

We propose a fast Computer-Generated Hologram (CGH) computation method with occlusion effect based on a hybrid point-source/wave-field approach. Whereas previously proposed methods tried to reduce the computational complexity of the point-source or the wave-field approaches independently, the proposed method uses the two approaches together and therefore takes advantages from both of them. Our algorithm consists of three steps. First, the 3D scene is sliced into several depth layers parallel to the hologram plane. Then, light scattered by the scene is propagated and shielded from one layer to another, starting from the farthest layer. For each layer, light propagation and light shielding are performed using either a point-source or a wave-field approach according to a threshold criterion on the number of points within the layer. Finally, we compute light propagation from the nearest layer to the hologram plane in order to obtain the final CGH. Experimental results reveal that this combination of approaches does not produce any visible artifact and outperforms both the point-source and wave-field approaches.

A framework for view-dependent hologram representation and adaptive reconstruction

In this paper, we present a framework for networked hologram adaptive transmission. Depending on the observer position, a subset of hologram data is transmitted and displayed. Wavelet decomposition and pruning of wavelet coefficients according to the user position allows local diffractive pattern extraction. The proposed framework has been validated on an experimental set-up involving a kinect sensor for viewer position estimation.

Fast generation of complex modulation video holograms using temporal redundancy compression and hybrid point-source/wave-field approaches

The hybrid point-source/wave-field method is a newly proposed approach for Computer-Generated Hologram (CGH) calculation, based on the slicing of the scene into several depth layers parallel to the hologram plane. The complex wave scattered by each depth layer is then computed using either a wave-field or a point-source approach according to a threshold criterion on the number of points within the layer. Finally, the complex waves scattered by all the depth layers are summed up in order to obtain the final CGH. Although outperforming both point-source and wave-field methods without producing any visible artifact, this approach has not yet been used for animated holograms, and the possible exploitation of temporal redundancies has not been studied. In this paper, we propose a fast computation of video holograms by taking into account those redundancies. Our algorithm consists of three steps. First, intensity and depth data of the current 3D video frame are extracted and compared with those of the previous frame in order to remove temporally redundant data. Then the CGH pattern for this compressed frame is generated using the hybrid point-source/wave-field approach. The resulting CGH pattern is finally transmitted to the video output and stored in the previous frame buffer. Experimental results reveal that our proposed method is able to produce video holograms at interactive rates without producing any visible artifact.