Speckle reduction for single sideband-encoded computer-generated holograms by using an optimized carrier wave.

Computer-generated hologram (CGH) is an evolving field that facilitates three-dimensional displays, with speckle noise reduction being a pivotal challenge. In hologram synthesis, complex data with random phase distributions are typically employed as carrier waves for wide viewing angles and a shallow depth of focus (DOF). However, these carrier waves are a source of speckle noise, which can significantly degrade image quality. In this paper, we propose a novel technique for speckle reduction for single sideband (SSB)-encoded holograms, applicable to any arbitrary 3D object. The proposed method focuses on optimizing the random carrier wave used in the hologram synthesis to achieve a uniform amplitude distribution at the object's location. This optimization results in a carrier wave that consistently exhibits uniform amplitude at specific depth planes, leading to a significant reduction of the speckle occurring from the carrier wave. The proposed method has been validated through simulations and optical experiments.

Non-hogel-based computer generated hologram with occlusion processing between the foreground light field and background hologram.

A novel technique is proposed to process the occlusion of a background hologram when synthesizing a front scene hologram from its light field. Unlike conventional techniques which process the occlusion in the light field domain after converting the background hologram to its light field, the proposed technique directly processes the occlusion between different domains, i.e., the background hologram and foreground light field. The key idea is to consider the background hologram as a carrier wave illuminating the front scene when synthesizing the front scene hologram from its light field. The proposed technique is not only computationally efficient as it does not require conversion between the light field and hologram domains but also accurate because all angular information of the background hologram and foreground light field is naturally considered in the occlusion processing. The proposed technique was verified by numerical synthesis and reconstruction.

Quality enhancement of binary-encoded amplitude holograms by using error diffusion.

A digital micro-mirror device is one of the most frequently used spatial light modulators for holographic three-dimensional displays due to its fast refresh rate. The modulation by the digital micro-mirror device is, however, limited to the binary amplitude modulation, and it degrades the reconstruction image quality. In this paper, we propose a novel binary hologram encoding technique which applies the error diffusion algorithm considering the carrier wave of the hologram. The error diffusion weights designed for the hologram carrier wave suppress the binarization noise around the carrier wave where the most signal energy is concentrated, which enhances the reconstruction quality. The combination with the time-multiplexing enables speckless enhanced-quality three-dimensional reconstruction with shallow depth of focus. The proposed technique is verified by simulations and optical experiments.