Color Computer-generated Holograms Research Articles

Compressing Color Computer-Generated Hologram Using Gradient Optimized Quantum-Inspired Neural Network

Compressing Color Computer-Generated Hologram Using Gradient Optimized Quantum-Inspired Neural Network

Color computer-generated hologram generation using the random phase-free method and color space conversion.

We propose two calculation methods of generating color computer-generated holograms (CGHs) with the random phase-free method and color space conversion in order to improve the image quality and accelerate the calculation. The random phase-free method improves the image quality in monochrome CGH, but it is not performed in color CGH. We first aimed to improve the image quality of color CGH using the random phase-free method and then to accelerate the color CGH generation with a combination of the random phase-free method and color space conversion method, which accelerates the color CGH calculation due to down-sampling of the color components converted by color space conversion. To overcome the problem of image quality degradation that occurs due to the down-sampling of random phases, the combination of the random phase-free method and color space conversion method improves the quality of reconstructed images and accelerates the color CGH calculation. We demonstrated the effectiveness of the proposed method in simulation, and in this paper discuss its application to lensless zoomable holographic projection.

Coding Color Three-Dimensional Scenes and Joining Different Objects by Adaptive Transformations in Digital Holography

We show that a three-dimensional (3D) scene can be coded by joining different objects by combining multiple optically recorded color digital holograms. Recently, an adaptive scheme based on affine transformations, able to correct defocus aberrations of digital holograms, was demonstrated, that we name here Adaptive Transformation in Digital Holography (ATDH). We propose an effective framework to create dynamic color holographic 3D scene by using a generalization of such scheme aided by a speckle reduction method, called Multilevel Bi-dimensional Empirical Mode Decomposition (MBEMD), used for the first time in color holography. We also demonstrate its feasibility to the synthesis of multiple Color Computer Generated Holograms (CCGHs).

Acceleration of color computer-generated hologram from RGB–D images using color space conversion

We report acceleration of color computer-generated holograms (CGHs) from three dimensional (3D) scenes that are expressed as RGB and depth (D) images. These images are captured by a depth camera and depth buffer of 3D graphics library. RGB and depth images preserve color and depth information of 3D scene, respectively. Then we can regard them as two-dimensional (2D) section images along the depth direction. In general, convolution-based diffraction such as the angular spectrum method is used in calculating CGHs from the 2D section images. However, it takes enormous amount of time because of multiple diffraction calculations. In this paper, we first describe “band-limited double-step Fresnel diffraction (BL-DSF)” which can accelerate the diffraction calculation than convolution-based diffraction. Next, we describe acceleration of color CGH using color space conversion. Color CGHs are generally calculated on RGB color space; however, we need to perform the same calculations for each color component repeatedly, so that computational cost of color CGH calculation is three times as that of monochrome CGH calculation. Instead, we use YCbCr color space because the 2D section images on YCbCr color space can be down-sampled without deterioration of the image quality.

Calculation reduction method for color digital holography and computer-generated hologram using color space conversion

A calculation reduction method for color digital holography (DH) and computer-generated holograms (CGHs) using color space conversion is reported. Color DH and color CGHs are generally calculated on RGB space. We calculate color DH and CGHs in other color spaces for accelerating the calculation (e.g., YCbCr color space). In YCbCr color space, a RGB image or RGB hologram is converted to the luminance component (Y), blue-difference chroma (Cb), and red-difference chroma (Cr) components. In terms of the human eye, although the negligible difference of the luminance component is well recognized, the difference of the other components is not. In this method, the luminance component is normal sampled and the chroma components are down-sampled. The down-sampling allows us to accelerate the calculation of the color DH and CGHs. We compute diffraction calculations from the components, and then we convert the diffracted results in YCbCr color space to RGB color space. The proposed method, which is possible to accelerate the calculations up to a factor of 3 in theory, accelerates the calculation over two times faster than the ones in RGB color space.

Wavelength-compensated color Fourier diffractive optical elements using a ferroelectric liquid crystal on silicon display and a color-filter wheel

In this work we describe the experimental realization of a simple scheme capable of implementing RGB improved dynamic color binary-phase Fourier computer-generated holograms (CGHs) by means of a single ferroelectric liquid crystal on silicon (FLCOS) display and an electronically controlled color-filter wheel. Tricolor multiwavelength illumination is achieved by aligning an Ar-Kr laser (wavelengths lambda(B)=488 nm and lambda(G)=568 nm) and a He-Ne laser ((R)=633 nm). Chromatic compensation is achieved by synchronizing a time sequence of properly scaled CGHs displayed on the FLCOS display with the corresponding filter from the color wheel. Quality CGHs are designed for each color component by using an optimized iterative Fourier transform algorithm applied to a phase-only modulation display. As a result, we present excellent experimental results on the reconstruction of these time-multiplexed wavelength-compensated diffractive optical elements and color CGHs.

Color computer-generated holograms from projection images

A novel method for the procurement of full-color three-dimensional (3-D) images of real objects has been developed. This method is based on extracting information from 3-D Fourier spectra, which are calculated from several projection images recorded using a white light source. 3-D Fourier spectra for three colors were obtained separately for projection images recorded with a color-CCD camera. Three computer-generated holograms (CGHs) were then synthesized from those Fourier spectra. The resulting numerically and optically reconstructed full-color images are presented.