Athanasia Symeonidou

Computer-generated holograms by multiple wavefront recording plane method with occlusion culling

We propose a novel fast method for full parallax computer-generated holograms with occlusion processing, suitable for volumetric data such as point clouds. A novel light wave propagation strategy relying on the sequential use of the wavefront recording plane method is proposed, which employs look-up tables in order to reduce the computational complexity in the calculation of the fields. Also, a novel technique for occlusion culling with little additional computation cost is introduced. Additionally, the method adheres a Gaussian distribution to the individual points in order to improve visual quality. Performance tests show that for a full-parallax high-definition CGH a speedup factor of more than 2,500 compared to the ray-tracing method can be achieved without hardware acceleration.

Three-dimensional rendering of computer-generated holograms acquired from point-clouds on light field displays

Holograms, either optically acquired or simulated numerically from 3D datasets, such as point clouds, have special rendering requirements for display. Evaluating the quality of hologram generation techniques is not straightforward, since high-quality holographic display technologies are still immature, In this paper we present a framework for three-dimensional rendering of colour computer-generated holograms (CGHs) acquired from point-clouds, on high-end light field displays. This allows for the rendering of holographic content with horizontal parallax and wide viewing angle. We deploy prior work, namely a fast CGH method that inherently handles occlusion problems to acquire high quality colour holograms from point clouds. Our experiments showed that rendering holograms with the proposed framework provides 3D effect with depth disparity and horizontal-only with wide viewing angle. Therefore, it allows for the evaluation of CGH techniques regarding functional properties such as depth cues and efficient occlusion handling.

Speckle noise reduction for computer generated holograms of objects with diffuse surfaces

Digital holography is mainly used today for metrology and microscopic imaging and is emerging as an important potential technology for future holographic television. To generate the holographic content, computer-generated holography (CGH) techniques convert geometric descriptions of a 3D scene content. To model different surface types, an accurate model of light propagation has to be considered, including for example, specular and diffuse reflection. In previous work, we proposed a fast CGH method for point cloud data using multiple wavefront recording planes, look-up tables (LUTs) and occlusion processing. This work extends our method to account for diffuse reflections, enabling rendering of deep 3D scenes in high resolution with wide viewing angle support. This is achieved by modifying the spectral response of the light propagation kernels contained by the look-up tables. However, holograms encoding diffuse reflective surfaces depict significant amounts of speckle noise, a problem inherent to holography. Hence, techniques to improve the reduce speckle noise are evaluated in this paper. Moreover, we propose as well a technique to suppress the aperture diffraction during numerical, viewdependent rendering by apodizing the hologram. Results are compared visually and in terms of their respective computational efficiency. The experiments show that by modelling diffuse reflection in the LUTs, a more realistic yet computationally efficient framework for generating high-resolution CGH is achieved.

Source coding of holographic data: challenges, algorithms and standardization efforts

Holographic imaging modalities are gaining increasing interest in various application domains ranging from microscopy to high-end autostereoscopic displays. While much effort has been spent on the development of the optics, photonics and micro/nano-electronics that enable the design of holographic capturing and visualization devices, relatively few research effort has been targeted towards the underlying signal processing. One significant challenge relates to the fact that the data volumes needed in support of this kind of holographic applications is rapidly increasing: for visualization devices, and in particular holographic displays, unprecedented resolutions are desired resulting in huge bandwidth requirements on both the communication channels and internal computing and data channels. An additional challenge relates to the fact that we are handling an interference-based modality being complex amplitude based in nature. Both challenges lead to the fact that for example classic data representations and coding solutions fail to handle holographic data in an effective way. This paper attempts to provide some insights that enable to alleviate or a least reduce these bottlenecks and sketch an avenue for the development of efficient source coding solutions. Moreover, it will also outline the efforts the JPEG committee is undertaking in the context of the JPEG Pleno standardization programme to roll out a path for data interoperability of holographic solutions.

Signal processing challenges for digital holographic video display systems

Abstract Holography is considered to be the ultimate display technology since it can account for all human visual cues such as stereopsis and eye focusing. Aside from hardware constraints for building holographic displays, there are still many research challenges regarding holographic signal processing that need to be tackled. In this overview, we delineate the steps needed to realize an end-to-end chain from digital content acquisition to display, involving the efficient generation, representation, coding and quality assessment of digital holograms. We discuss the current state-of-the-art and what hurdles remain to be taken to pave the way towards realistic visualization of dynamic holographic content.

A Roadmap Towards Holographic Television From a Signal Processing Perspective

In recent years, the domain of plenoptic imaging has seen significant scientific and industrial evolutions. We present novel signal processing technologies addressing holographic imaging, ranging from capture to rendering of complex amplitude digital holograms.