Method of single-step full parallax synthetic holographic stereogram printing based on effective perspective images' segmentation and mosaicking

Analog-to-digital conversion of information archived in display holograms: I. discussion

This discussion paper highlights the potential of display holograms in the storage of information about objects' shape. The images recorded and reconstructed from holograms have high visual appeal, and the holographic carrier has far higher information capacity than other storage media. One hindrance to the application of display holograms is the inadequate development of techniques for digitizing information from them, which is compounded by insufficient analysis and discussion of existing approaches. In this review, we provide a historical retrospective of the use of display holography to save comprehensive information on object morphology. We also discuss existing and emerging technologies for converting information into a digital format, addressing one of the most serious challenges to the widespread use of display holography. Potential applications of these technologies are also analyzed.

Perspective clipping and fast rendering of light field images for holographic stereograms using RGBD data

The production of holographic stereogram (HS) requires a huge amount of light field data. How to efficiently clip and render these image data remains a challenge in the field. This work focuses on the perspective clipping and fast rendering algorithm for light field images using RGBD data without explicit 3D reconstruction. The RGBD data is expanded to RGBDθ data by introducing a light cone for each point, which gives a new degree of freedom for light field image rendering. Using the light cone and perspective coherence, the visibility of 3D image points can be clipped programmatically. Optical imaging effects including mirror imaging and half mirror imaging effects of 3D images can also be rendered with the help of light cones during the light field rendering process. The perspective coherence is also used to accelerate the rendering, which has been shown to be on average 168% faster than traditional DIBR algorithms. A homemade holographic printing system was developed to make the HSs using the rendered light field images. The vivid 3D effects of the HS have validated the effectiveness of the proposed method. It can also be used in holographic dynamic 3D display, augmented reality, virtual reality, and other fields.

Implementation of the real-virtual 3D scene-fused full-parallax holographic stereogram

This work focuses on the generation of three-dimensional (3D)-scene information as well as the fusion of real and virtual 3D scene information for the full-parallax holographic stereogram based on the effective perspective images' segmentation and mosaicking (EPISM) method. The improved depth-image-based rendering (DIBR) method was used to generate the virtual viewpoint images of the real 3D scene, and the regularization and densification processing models of the degraded light field were established; as a result, the real sampling-light field was reconstructed. Combined with the computer-rendered virtual 3D scene information, a "real + virtual" light-field fusion method based on a pixel-affine-projection was proposed to realize the fusion of the real and virtual 3D scene. The fusion information was then processed by the EPISM encoding and was then holographically printed. The optical experiment results showed that the full-parallax holographic stereogram with the real-virtual scene-fused 3D scenes could be correctly printed and reconstructed, which validated the effectiveness of our proposed method.

High-quality holographic stereogram generation using four RGBD images

To computer-generate high-quality holographic stereograms, a huge number of images must be provided: several hundred for a horizontal parallax and the square of this number for a full parallax. In this paper, we propose to drastically reduce this number to four input images with depth maps (or equivalently, four groups of neighboring images used to compute a depth map) in any pose, in order to create the missing images with depth image-based rendering. We evaluate the view synthesis method objectively before providing visual results of the corresponding holographic stereograms. We believe this method outperforms shearlet-based approaches in objective view synthesis quality metrics and in the number of required input images (7×7).

Efficient Hogel-Based Hologram Synthesis Method for Holographic Stereogram Printing

With the development of the holographic printer, printing synthetic hologram requires smaller holographic element (hogel) size to improve spatial resolution of the reconstruction. On the contrary, a larger hogel size affords higher angular resolution, but it leads to a lower lateral resolution and there exists a trade-off problem. In this paper, a hologram synthesis method based on three-dimensional (3D) rendering of computer-generated holographic stereogram (HS) is proposed to limit the spatial-angular trade-off problem. The perspectives of the 3D scene are captured by re-centering the camera method and transformed into parallax-related images by a proposed pixel re-arrangement algorithm for holographic printing. Unlike the conventional approaches, the proposed algorithm not only improves the angular resolution of the reconstruction while maintaining the hogel size fixed, but also keeps the spatial resolution without degradation. The effectiveness of the proposed method is verified by numerical simulation and an optical experiment.

View-flipping effect reduction and reconstruction visualization enhancement for EPISM based holographic stereogram with optimized hogel size

To reduce the view-flipping effect and enhance the viewing resolution, the modulation characteristics of the hogel based holographic stereogram is constructed and validated. The performance of the view-flipping effect is analyzed, and the results indicate that decreasing the size of hogel is beneficial to the reduction of the view flipping, however, which will result in significant diffraction effect which can degrade the reconstruction quality. Furthermore, a diffraction-limited imaging model of the hogel based holographic stereogram is established, where both the limited aperture of the hogel and the defocused aberration of the object point are introduced, and the effective resolvable size of the reconstructed image point is simulated. The theory shows that there is an optimal hogel size existed for the certain depth of scene. Both the numerical and optical experiments are implemented, and the results are well agreed with the theoretical prediction, which demonstrates that the view-flipping reduction and reconstruction visualization enhancement for EPISM based holographic stereogram can be achieved when the proper size of hogel is utilized.

CHIMERA, a new holoprinter technology combining low-power continuous lasers and fast printing

This paper presents CHIMERA, a third-generation digital holographic printing system that solves the known problems of the two previous generations. This holoprinter is based on the use of low-power RGB continuous lasers combined with the ultrafine-grain silver-halide material Ultimate U04 and is capable of printing at a frequency equal to or greater than 25 hogels per second, full-color, 120° full-parallax digital reflection holograms or holographic optical elements with a size of up to 60×80cm and a hogel size ranging from 250 to 500 µm. A 3D scanner using a 4K video camera has been specially designed for scanning real objects printable on CHIMERA, which offers new achievements in terms of color rendition, palette, and accuracy and opens new perspectives for digital holography applications and holography in general.

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.

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.

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.

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.

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.

Characteristic and optimization of the effective perspective images' 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.