Holographic Stereogram Research Articles

Performance Improvement for Computer-Generated Holographic Stereogram Based on Integral Imaging

Performance Improvement for Computer-Generated Holographic Stereogram Based on Integral Imaging

Performance Improvement for Computer-Generated Holographic Stereogram Based on Integral Imaging

Performance Improvement for Computer-Generated Holographic Stereogram Based on Integral Imaging

Centered-camera-based effective perspective images' segmentation and mosaicking method for full-parallax holographic stereogram printing.

The centered-camera-based effective perspective images' segmentation and mosaicking (CCEPISM) method is proposed to improve the previous EPISM-based printing of full-parallax holographic stereograms. The idea of pixel mapping from target camera images to centered camera images is analyzed, and backward pixel mapping as well as forward pixel mapping are modeled and formulated to transform the perspective images captured by different camera strategies. The principle of the proposed CCEPISM is introduced in detail along with its specific implementation. The experimental results validate the proposed method and demonstrate that CCEPISM is an effective method for printing full-parallax holographic stereograms, and the quality of optical reconstruction is the same as that of EPISM-based holographic stereograms. The whole 3D scene is captured by a centered camera image, and the pixel waste caused by simple camera capture and the number of sampled perspective images is reduced significantly.

Holographic near-eye displays based on overlap-add stereograms

Holographic near-eye displays are a key enabling technology for virtual and augmented reality (VR/AR) applications. Holographic stereograms (HS) are a method of encoding a light field into a hologram, which enables them to natively support view-dependent lighting effects. However, existing HS algorithms require the choice of a hogel size, forcing a tradeoff between spatial and angular resolution. Based on the fact that the short-time Fourier transform (STFT) connects a hologram to its observable light field, we develop the overlap-add stereogram (OLAS) as the correct method of "inverting" the light field into a hologram via the STFT. The OLAS makes more efficient use of the information contained within the light field than previous HS algorithms, exhibiting better image quality at a range of distances and hogel sizes. Most remarkably, the OLAS does not degrade spatial resolution with increasing hogel size, overcoming the spatio-angular resolution tradeoff that previous HS algorithms face. Importantly, the optimal hogel size of previous methods typically varies with the depth of every object in a scene, making the OLAS not only a hogel size-invariant method, but also nearly scene independent. We demonstrate the performance of the OLAS both in simulation and on a prototype near-eye display system, showing focusing capabilities and view-dependent effects.

Analysis on the reconstruction error of EPISM based full-parallax holographic stereogram and its improvement with multiple reference plane.

To reduce the reconstruction error of holographic stereogram fabricated by effective perspective images' segmentation and mosaicking method (EPISM), a multiple-reference-plane (MRP) approach is proposed and validated. The reconstruction error for traditional EPISM is analyzed, and the results indicate that the distortion as well as the blur will be involved for object points located far away from the reference plane. A new method by introducing multiple reference planes is proposed, which divides the 3D scene into several parts along its depth direction, and sets a reference plane for each of the object part. By resynthesizing all the effectively synthetic perspective images referred to their own reference planes of the object parts, the finally effectively synthetic perspective image exposed to one holographic elemental by only once exposure is generated. The optically experimental results demonstrate the validity of the proposed method, and the reconstruction error of full-parallax holographic stereogram printed by MRP based EPISM can be reduced evidently while the displayed depth range of 3D scene can be extended, compared to the traditional EPISM approach.

Resolution-enhanced holographic stereogram based on integral imaging using a moving array lenslet technique and an aperture array filter.

A method in which an integral-imaging-based holographic stereogram (HS) using a moving array lenslet technique (MALT) and aperture array filter toward improving the resolution of a reconstructed three-dimensional (3D) image is presented. The previous resolution-enhanced HS using the MALT method only considered enhancement of the sampling rate without decreasing the volume pixels (voxels) size. The voxels are created by multiple plane waves in different directions emitting from holographic elements (hogels), and the voxel size is equal to the width of plane waves. In order to further improve the resolution of the reconstructed image quality, an aperture array filter is applied to allow the center square part of each plane wave to pass and filter the rest. The filtering process reduces the width of plane waves, and decreases the voxel size as well. The proposed method has a high sampling rate and can reconstruct the 3D image with smaller voxels. The image quality improvement is verified in numerical and optical reconstruction compared to theHSusingMALTalone.

Resolution-enhanced holographic stereogram based on integral imaging using an intermediate-view synthesis technique

We proposed a resolution-enhanced integral imaging (II) based holographic stereogram (HS) using an intermediate-view synthesis (IVS) technique. The HS can be generated fast by Fourier transforming the elemental images of II into hogels. However, the low sampling rate of II is inherited in HS. In this paper, a simple IVS technique is proposed to synthesize intermediate-view elemental images and then adopted to improve the sampling rate of II-based HS. The proposed method avoids multiple captures which are usually realized through the moving array lenslet technique (MALT). Multiple intermediate-view elemental image arrays (IEIAs) are digitally synthesized from an original elemental image array (EIA) with IVS. The original EIA and synthesized IEIAs are transformed to the corresponding HS sequences. All the HS sequences are shifted and added together in one hologram pattern to synthesize the HS with a high sampling rate. Superior to the MALT in II, this method does not need the time-multiplexing technique in both capture stage and display stage. The 3D image quality improvement was verified in numerical and optical reconstruction.

Dual-view holographic stereogram 3D display based on integral imaging

Conventional dual-view integral imaging (II) three-dimensional (3D) display has the disadvantage of information halving in each viewing zone. We propose a holographic stereogram (HS) type dual-view 3D display without information halving in each viewing zone. The HS can be generated fast by Fourier transforming the elemental images of II into hologram elements (hogels). With shifted Fourier transform, each hogel is generated with a rotated viewing zone. By adjusting the viewing zone of each hogel to make them converge at a specific distance, a specific viewing zone is generated. Then, by adding the two holograms together, each of which corresponds to a separate viewing zone, a dual-view HS is obtained without halving the information presented in each viewing zone. The proposed method is verified through simulation and optical experiment.

Holographic Element-Based Effective Perspective Image Segmentation and Mosaicking Holographic Stereogram Printing

Effective perspective image segmentation and mosaicking (EPISM) method is an effective holographic stereogram printing method, but a mosaic misplacement of reconstruction image occurred when focusing away from the reconstruction image plane. In this paper, a method known as holographic element-based effective perspective image segmentation and mosaicking is proposed. Holographic element (hogel) correspondence is used in EPISM method as pixel correspondence is used in direct-writing digital holography (DWDH) method to generate effective perspective images segments. The synthetic perspective image for holographic stereogram printing is obtained by mosaicking all the effective perspective images segments. Optical experiments verified that the holographic stereogram printed by the proposed method can provide high-quality reconstruction imagery and solve the mosaic misplacement inherent in the EPISM method.

Resolution priority holographic stereogram based on integral imaging with enhanced depth range.

Conventional holographic stereogram (HS) can be generated through fast Fourier transforming parallax images into hogels. Conventional HS uses multiple plane waves to reconstruct 3D images with low resolution and is similar to the principle of depth priority integral imaging (II). We proposed the concept of resolution priority HS for the first time, which is based on the principle of resolution priority II, by adding a quadratic phase term on the conventional Fourier transform. In the proposed resolution priority HS, the resolution of reconstructed 3D images is much better than conventional HS, but the depth range is limited. To enhance the depth range, a multi-plane technique was used to present multiple central depth planes simultaneously. The proposed resolution priority HS with high resolution and enhanced depth range was verified by both simulation and optical experiment.

全息体视图打印技术进展综述

全息体视图打印技术进展综述

Material Design of Azo‐Carbazole Copolymers for Preservation Stability with Rewritable Holographic Stereograms

Material Design of Azo‐Carbazole Copolymers for Preservation Stability with Rewritable Holographic Stereograms

赝像-正像转换算法在全息体视图打印中的应用

赝像-正像转换算法在全息体视图打印中的应用

Characteristic and improvement on the reconstructed quality of effective perspective images’ segmentation and mosaicking-based holographic stereogram

Based on the effective perspective images' segmentation and mosaicking (EPISM) printing method, the influence of the holographic element (hogel) size on the reconstructed quality is analyzed to improve the reconstructed quality of holographic stereogram. The flipping effect and diffraction effect in the spatial domain are also discussed, and the optical transfer function of the holographic stereogram is used in the spectrum domain to evaluate the reconstructed quality. Theoretical analysis and optical experimental results show that the hogel size plays an important role on the flipping effect as well as the clarity of the reconstrued 3D perspective images of the EPISM-based holographic stereogram, and the flipping effect can be improved significantly with optimized hogel size.

Material Design of Azo‐Carbazole Copolymers for Preservation Stability with Rewritable Holographic Stereograms

AbstractIn the practical use of rewritable holographic stereograms, azobenzene‐functionalized polymers with high diffraction efficiency, fast response time, preservation stability, rewritability, and optical transparency capabilities are of extreme importance. Two novel azobenzene‐functionalized copolymers consisting of a 3‐[(4‐cyanophenyl)azo]‐9H‐carbazole‐9‐ethyl acrylate (acrylate monomer with CACzE) with methyl methacrylate (MMA) (poly(CACzE‐MMA)) and an ethyl methacrylate, EMA (poly(CACzE‐EMA)) are synthesized. Their holographic properties are evaluated through Raman–Nath diffraction characteristics, angular dependence of absorbance, and polarized Raman spectra. Between them, a material with the most excellent characteristics is a poly(CACzE‐MMA)/CACzE (50/15 wt%) composite. As a result, a first‐order diffraction efficiency (η1 ), grating formation speed (response time) (τ ), and retention ratios (R300s% and R50day%) in the poly(CACzE‐MMA)/CACzE (50/15 wt%) composite show 31.2%, 2.0 s, 100%, and 80%, respectively, in which a dichroism degree of 64.2° and refractive index modulation Δn of 0.00801 are achieved. Additionally, the holographic stereogram obtained with the poly(CACzE‐MMA)/CACzE (50/15 wt%) composite can be refreshed to its original state by heat treatment. The holographic properties of the poly(CACzE‐MMA)/CACzE (50/15 wt%) composite will be a contribution to the application of updatable holographic stereograms.

Resolution-enhanced holographic stereogram based on integral imaging using moving array lenslet technique

We proposed a resolution-enhanced integral imaging (II) based holographic stereogram (HS) using the moving array lenslet technique (MALT). The HS can be generated fast by Fourier transforming the elemental images of II into hogels. However, the low sampling rate of II is inherited in HS. The MALT was introduced to increase the sampling rate of II-based HS. Multiple elemental image array sequences are captured with MALT and transformed to the corresponding HS sequences. All the HS sequences are shifted depending on the movement of the lens array and added together to synthesize the HS with a high sampling rate. The synthesized HS can reconstruct the 3D image with the combined light fields of all the HS sequences. The 3D image quality improvement was verified in numerical and optical reconstruction. Superior to the MALT in II, this method does not need the time-multiplexing technique in the display stage because different HS sequences are displayed in one hologram pattern simultaneously.

Highly efficient calculation method for computer-generated holographic stereogram using a lookup table.

A highly efficient calculation method to synthesize a computer-generated holographic stereogram using a lookup table (LUT) is proposed. The complete phase distribution (CPD) of a spherical wave that is larger than the hologram is precalculated and stored as a LUT. The wavefront converging to each viewpoint can be directly obtained by adding a specific part of the precalculated CPD to the parallax image, instead of computing the wavefronts pixel by pixel in the conventional method. The computation amount and calculation time are effectively reduced to one-third of the conventional method. The working memory size is reduced effectively using the symmetry of the phase distributions of different viewpoints. A simulation and an optical experiment are performed to verify the proposed method.

Improvement of printing efficiency in holographic stereogram printing with the combination of a field lens and holographic diffuser.

In this paper, we use a field lens and a holographic diffuser together to improve the printing efficiency of a holographic stereogram printing system based on the effective perspective images' segmentation and mosaicking method. The light rays' regulation function of the field lens and the modulation function of the holographic diffuser are analyzed. Holographic diffusers with different expanding angles are optimized by numerical simulations and verified by optical experiments. We can achieve a better holographic stereogram reconstruction effect as well as a better printing efficiency when adopting a field lens and a 10° holographic diffuser together. With the proposed method, the energy efficiency can be improved, and the printing time can be reduced greatly.

Progress in the Synthetic Holographic Stereogram Printing Technique

The synthetic holographic stereogram printing technique can achieve a three-dimensional (3D) display of a scene. The development and research status of the synthetic holographic stereogram printing technique is introduced in this paper. We propose a two-step method, an infinite viewpoint camera method, a single-step Lippmann method, a direct-write digital holography (DWDH) method and an effective perspective images’ segmentation and mosaicking (EPISM) method. The synthetic holographic stereogram printing technique is described, including the holographic display with large format, the large field of view with no distortion, the printing efficiency, the color reproduction characteristics, the imaging quality, the diffraction efficiency, the development of a holographic recording medium, the noise reduction, and the frequency response analysis of holographic stereograms.

Characteristic and optimization of the effective perspective images\u2019 segmentation and mosaicking (EPISM) based holographic stereogram: an optical transfer function approach

Based on our proposed method for holographic stereogram printing using effective perspective images’ segmentation and mosaicking (EPISM), we analyze the reconstructed wavefront errors, and establish the exit pupil function model of proposed printing system. To evaluate the imaging quality, the optical transfer function (OTF) of the holographic stereogram is modelled from the aspect of frequency response. The characteristic of the OTF with respect to the exit pupil size and the aberration are investigated in detail. We also consider the flipping effect in spatial domain. The optimization of hogel sizes, i.e., the sampling interval of original perspective images and the printing interval of synthetic effective perspective images, are given for the optimized reconstruction. Numerical simulations and optical experiments are implemented, and the results demonstrate the validity of our analysis, and the optimized parameters of hogel sizes can improve the imaging quality of full parallax holographic stereogram effectively.