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

Abstract

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.

Recent Advances in the Processing and Rendering Algorithms for Computer-Generated Holography

“…The sources of 2D holograms are two-dimensional images, while the sources of three-dimensional samples are point clouds. The generation algorithm has been improved in [59], including, in addition to occlusion, the simulation of diffuse light reflection from surfaces: the light is spread over a wide angle, providing an extended view of the scene with full parallax support. This dataset is called Interfere II and includes 6 diffuse and 6 specular monochromatic samples, generated from point clouds.…”

Digital holography data compression

“…The first sample belongs to the Interfere II dataset. As suggested by the authors in [50], the observation window has resolution of 2048×2048, and it is apodized using a 2-D Hanning window before the reconstruction process. In order to reduce the speckle noise, the final image is the average of three reconstructions performed at three different wavelengths (633nm, 632.9nm, and 633.1nm).…”

“…The dataset Interfere II [50] presents holograms created using a method that supports occlusion and simulation of diffuse reflection from surfaces. All the holograms are monochromatic, generated from point clouds.…”

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

“…To account for diffuse reflections, the spectral response of the look-up table content is modified with random phase, as described in Ref. 16, so that light is scattered over a wide angular range and consequently provides with a wide field of view. Inverted Gaussian filters are used in the propagation process to model occlusions by locally blocking light.…”

“…The extracted aperture from the hologram can produce aperture diffraction during numerical reconstruction, due to the sharp intensity edges of the rectangular aperture, therefore apodization is proposed 19,16 . This method smoothly brings the aperture edges to zero, as it suppresses side lobes leakage which would otherwise be produced upon propagation.…”