Wavefront Recording Plane Research Articles

Rapid hologram generation through backward ray tracing and adaptive-resolution wavefront recording plane

Abstract An advanced method for rapidly computing holograms of large three-dimensional (3D) objects combines backward ray tracing with adaptive resolution wavefront recording plane (WRP) and adaptive angular spectrum propagation. In the initial phase, a WRP with adjustable resolution and sampling interval based on the object’s size is defined to capture detailed information from large 3D objects. The second phase employs an adaptive angular spectrum method (ASM) to efficiently compute the propagation from the large-sized WRP to the small-sized computer-generated hologram (CGH). The computation process is accelerated using CUDA and OptiX. Optical experiments confirm that the algorithm can generate high-quality holograms with shadow and occlusion effects at a resolution of 1024 × 1024 in 29 ms.

Fast Hologram Calculation Method Based on Wavefront Precise Diffraction.

In this paper, a fast hologram calculation method based on wavefront precise diffraction is proposed. By analyzing the diffraction characteristics of the object point on the 3D object, the effective viewing area of the reproduced image is analyzed. Based on the effective viewing area, the effective hologram size of the object point is obtained, and then the accurate diffraction calculation from the object point to the wavefront recording plane (WRP) is performed. By calculating all the object points on the recorded object, the optimized WRP of the whole 3D object can be obtained. The final hologram is obtained by calculating the diffraction light field from the WRP to the holographic plane. Compared with the traditional method, the proposed method can improve the calculation speed by more than 55%, while the image quality of the holographic 3D display is not affected. The proposed calculation method provides an idea for fast calculation of holograms and is expected to contribute to the development of dynamic holographic displays.

A Full-Color Holographic System Based on Taylor Rayleigh–Sommerfeld Diffraction Point Cloud Grid Algorithm

Real objects-based full-color holographic display systems usually collect data with a depth camera and then modulate the input light source to reconstruct the color three-dimensional scene of the real object. However, at present, the main problems of the real-time high quality full-color 3D display are slow speed, low reconstruction quality, and high consumption of hardware resources caused by excessive computing. Based on the hybrid Taylor Rayleigh–Sommerfeld diffraction algorithm and previous studies on full-color holographic systems, our paper proposes Taylor Rayleigh–Sommerfeld diffraction point cloud grid algorithm (TR-PCG), which is to perform Taylor expansion on the radial value of Rayleigh–Sommerfeld diffraction in the hologram generation stage and modify the data type to effectively accelerate the calculation speed and ensure the reconstruction quality. Compared with the wave-front recording plane, traditional point cloud gridding (PCG), C-PCG, and Rayleigh–Sommerfeld PCG without Taylor expansion, the computational complexity is significantly reduced. We demonstrate the feasibility of the proposed method through experiments.

Wavefront recording plane-like method for polygon-based holograms.

The wavefront recording plane (WRP) method is an algorithm for computer-generated holograms, which has significantly promoted the accelerated computation of point-based holograms. Similarly, in this paper, we propose a WRP-like method for polygon-based holograms. A WRP is placed near the object, and the diffracted fields of all polygons are aggregated in the WRP so that the fields propagating from the polygonal mesh affect only a small region of the plane rather than the full region. Unlike the conventional WRP method used in point-based holograms, the proposed WRP-like method utilizes sparse sampling in the frequency domain to significantly reduce the practical computational kernel size. The proposed WRP-like method and the analytical shading model are used to generate polygon-based holograms of multiple three-dimensional (3D) objects, which are then reproduced to confirm 3D perception. The results indicate that the proposed WRP-like method based on an analytical algorithm is hundreds of times faster than the reference full region sampling case; a hologram with tens of thousands of triangles can be computed in seconds even on a CPU, whereas previous methods required a graphics processing unit to achieve these speeds.

Accelerating hologram generation using oriented-separable convolution and wavefront recording planes.

Recently, holographic displays have gained attention owing to their natural presentation of three-dimensional (3D) images; however, the enormous amount of computation has hindered their applicability. This study proposes an oriented-separable convolution accelerated using the wavefront-recording plane (WRP) method and recurrence formulas. We discuss the orientation of 3D objects that affects computational efficiency, which is overcome by reconsidering the orientation, and the suitability of the proposed method for hardware implementations.

Segmented Point Cloud Gridding Method for a Full-Color Holographic System With Real Objects

The large amount of computing data from hologram calculations incurs a heavy computational load for realistic full-color holographic displays. In this research, we propose a segmented point-cloud gridding (S-PCG) method to enhance the computing ability of a full-color holographic system. A depth camera is used to collect the color and depth information from actual scenes, which are then reconstructed into the point-cloud model. Object points are categorized into depth grids with identical depth values in the red, green, and blue (RGB) channels. In each channel, the depth grids are segmented into M×N parts, and only the effective area of the depth grids will be calculated. Computer-generated holograms (CGHs) are generated from efficient depth grids by using a fast Fourier transform (FFT). Compared to the wavefront recording plane (WRP) and traditional PCG methods, the computational complexity is dramatically reduced. The feasibility of the S-PCG approach is established through numerical simulations and optical reconstructions.

Recent Advances in Development of Fast Algorithms for Computed Hologram Generation Using Wavefront Recording Plane Technique

Recent Advances in Development of Fast Algorithms for Computed Hologram Generation Using Wavefront Recording Plane Technique

Hologram computation using the radial point spread function.

Holograms are computed by superimposing point spread functions (PSFs), which represent the distribution of light on the hologram plane. The computational cost and the spatial bandwidth product required to generate holograms are significant; therefore, it is challenging to compute high-resolution holograms at the rates required for videos. Among the possible displays, fixed-eye-position holographic displays, such as holographic head-mounted displays, reduce the spatial bandwidth product by fixing eye positions while satisfying almost all human depth cues. In eye-fixed holograms, by calculating a part distribution of the entire PSF, we observe reconstructed images that maintain the image quality and the depth of focus almost as high as those generated by the entire PSF. In this study, we accelerate the calculation of eye-fixed holograms by engineering the PSFs. We propose cross and radial PSFs, and we determine that, out of the two, the radial PSFs have a better image quality. By combining the look-up table method and the wavefront-recording plane method with radial PSFs, we show that the proposed method can rapidly compute holograms.

Acceleration of fully computed hologram stereogram using lookup table and wavefront recording plane methods.

Lookup table (LUT) and wavefront recording plane (WRP) methods are proposed to accelerate the computation of fully computed hologram stereograms (HSs). In the LUT method, we precalculate large and complete spherical wave phases with varying depths, and each complex amplitude distribution segment of the object point can be obtained quickly by cropping a specific and small part of the precalculated spherical wave phases. Then, each hologram element (hogel) can be calculated by superposing all the related segments. In addition, setting a WRP near the 3D scene can further accelerate computation and reduce storage space. Because the proposed methods only replace the complex calculation using referencing LUT, they are accurate and have no limitation on the size of hogel compared with some methods of paraxial approximation. Simulations and optical experiments verify that the proposed methods can reconstruct quality 3D images with reduced computational load.

Acceleration and expansion of a photorealistic computer-generated hologram using backward ray tracing and multiple off-axis wavefront recording plane methods

Holograms can reconstruct the light wave field of three-dimensional objects. However, the computer-generated hologram (CGH) requires much calculating time. Here we proposed a CGH generation algorithm based on backward ray tracing and multiple off-axis wavefront recording planes (MO-WRP) to generate photorealistic CGH with a large reconstruction image. In this method, multiple WRPs were placed parallelly between the virtual object and the hologram plane. Virtual rays were emitted from the pixel of WRPs and intersect with the object. The complex amplitude of WRPs is then determined by illumination module, such as Phong reflection module. The CGH was generated by the shifted Angular Spectrum Propagation (ASP) from WRPs to the hologram plane. Experimental results demonstrate the effectiveness of this method, and the CGH generation rate is 37.3 frames per second (1 WRP) and 9.8 frames per second (2×2 WRPs).

Fast Diffraction Calculation for Spherical Computer-Generated Hologram Using Phase Compensation Method in Visible Range

The synthesis of the spherical hologram has been widely investigated in recent years as it enables a large field of view both horizontally and vertically. However, there is an important issue of long time consumption in spherical computer-generated holograms (SCGHs). To address this issue, a fast diffraction calculation method is proposed for SCGH based on phase compensation (PC). In our method, a wavefront recording plane (WRP) near the SCGH is used to record the diffraction distribution from the object plane, and the phase difference is compensated point-to-point from the WRP to generate the SCGH, during which a nonuniform sampling method is proposed to greatly decrease the sampling rate and significantly accelerate the generation speed of SCGH. In this paper, there are three main contributions: (1) SCGHs with the resolution of full high-definition can be synthesized in visible range with reducing the sampling rate. (2) Due to the current difficulty of realizing holographic display with curved surfaces, our PC method provides an alternative approach to implement optical experiments of SCGH, which takes it closer to the practical applications of spherical holography. (3) The problem of time-consuming calculation of the propagation model between plane and sphere is solved firstly to our best knowledge.

Improving the quality of full-color holographic three-dimensional displays using depth-related multiple wavefront recording planes with uniform active areas.

In this paper, a depth-related uniform multiple wavefront recording plane (UM-WRP) method is proposed for enhancing the image quality of point cloud-based holograms. Conventional multiple WRP methods, based on full-color computer-generated holograms, experience a color uniformity problem caused by intensity distributions. To solve this problem, the proposed method generates depth-related WRPs to enhance color uniformity, thereby accelerating hologram generation using a uniform active area. The aim is to calculate depth-related WRPs with designed active area sizes that then propagate to the hologram. Compared with conventional multiple WRP methods, reconstructed images have significantly improved quality, as confirmed by numerical simulations and optical experiments.

Image quality improvement of holographic 3-D images based on a wavefront recording plane method with a limiting diffraction region.

This study aims to improve the image quality of holographic three-dimensional (3-D) images based on the wavefront recording plane (WRP) method. In this method, we place a WRP close to the 3-D objects to reduce the propagation distance of light from the objects to the WRP. The conventional WRP method has been implemented only under conditions that did not cause aliasing noise. This study proposes a WRP method with a limiting diffraction region from the WRP to the hologram such that we can perform the WRP method under any condition. As a result, we succeeded in improving the image quality of the 3-D images based on the WRP method.

Fast method for calculating a curved hologram in a holographic display.

A curved hologram can increase the view angle in a holographic display. The huge data processing and curved computer-generated hologram (CCGH) computation time is still a challenge for real-time display. Here, we propose two fast methods to accelerate the computation. The first one is a diffraction compensation (DC) method where the diffraction calculation is from the wave-front recording plane (WRP) to a CCGH. The other is an approximate compensation (AC) method that adds a phase difference distribution to the WRP to obtain the CCGH. Numerical simulations and optical experiments are performed, which demonstrate that the two methods are feasible and the computation time is dramatically reduced. The AC method can further reduce time significantly compared with the DC method. And the image quality for proposed methods is similar. It is expected that these fast methods can be combined with curved display screen and flexible display materials in the future.

Max-depth-range technique for faster full-color hologram generation.

In this paper, a max-depth-range method is proposed to determine the optimum length of depth range for faster generation of full-color holograms. For each color channel, objects are divided by a fixed length to create a temporary depth range, and the wavefront recording plane (WRP) is placed in the middle of all layers within the temporary depth range. The proposed method is used to calculate full-color holograms significantly faster than a conventional multiple-WRP method but with almost the same reconstructed image quality. The feasibility of the proposed method was confirmed using numerical and optical experiments for various scenes containing multiple real objects.

Acceleration of computer-generated hologram using wavefront-recording plane and look-up table in three-dimensional holographic display.

In this paper, we propose a fast calculation method using look-up table and wavefront-recording plane. Wavefront-recording plane method consists of two steps: the first step is the calculation of a wavefront-recording plane which is placed between the object and the hologram. In the second step, we obtain the hologram by executing diffraction calculation from the wavefront-recording plane to the hologram plane. The first step of the previous wavefront-recording plane method is time consuming. In order to obtain further acceleration to the first step, we propose high compressed look-up table method based on wavefront-recording plane. We perform numerical simulations and optical experiments to verify the proposed method. Numerical simulation results show that the calculation time reduces dramatically in comparison with previous wavefront-recording plane method and the memory usage is very small. The optical experimental results are in accord with the numerical simulation results. It is expected that proposed method can greatly reduce the computational complexity and could be widely applied in the holographic field in the future.

Comparison of wavefront recording plane-based hologram calculations: ray-tracing method versus look-up table method.

In this study, we compare the ray-tracing method with the look-up table (LUT) method in order to optimize computer-generated hologram (CGH) calculation based on the wavefront recording plane (WRP) method. The speed of the WRP-based CGH calculation largely depends on implementation factors, such as calculation methods, hardware, and parallelization method. Therefore, we evaluated the calculation time and image quality of the reconstructed three-dimensional (3D) image by using the ray-tracing and LUT methods in the central processing unit (CPU) and graphics processing unit (GPU) implementations. Thereafter, we performed several implementations by changing the number of object points and the distance from 3D objects to the WRP. Furthermore, we confirmed different characteristics between CPU and GPU implementations.

Implementation of full-color holographic system using non-uniformly sampled 2D images and compressed point cloud gridding.

A multiple-camera holographic system using non-uniformly sampled 2D images and compressed point cloud gridding (C-PCG) is suggested. High-quality, digital single-lens reflex cameras are used to acquire the depth and color information from real scenes; these are then virtually reconstructed by the uniform point cloud using a non-uniform sampling method. The C-PCG method is proposed to generate efficient depth grids by classifying groups of object points with the same depth values in the red, green, and blue channels. Holograms are obtained by applying fast Fourier transform diffraction calculations to the grids. Compared to wave-front recording plane methods, the quality of the reconstructed images is substantially better, and the computational complexity is dramatically reduced. The feasibility of our method is confirmed both numerically and optically.

Stereoscopic hologram calculation based on nonuniform sampled wavefront recording plane

We propose a method of efficiently calculating computer-generated hologram for holographic stereoscopic display. The stereoscopic hologram is generated by sequentially tiling all the hogels that are calculated from respective parallax intensity and depth maps based on nonuniform sampled wavefront recording plane (NS-WRP) algorithm. The whole computational procedure is simplified by diffraction calculation of hogels from 2D planar images of each viewpoint, instead of massive 3D point-source. Numerical and optical experiments are carried out to confirm the feasibility of the proposed method.

Accelerated computer generated holography using sparse bases in the STFT domain.

Computer-generated holography at high resolutions is a computationally intensive task. Efficient algorithms are needed to generate holograms at acceptable speeds, especially for real-time and interactive applications such as holographic displays. We propose a novel technique to generate holograms using a sparse basis representation in the short-time Fourier space combined with a wavefront-recording plane placed in the middle of the 3D object. By computing the point spread functions in the transform domain, we update only a small subset of the precomputed largest-magnitude coefficients to significantly accelerate the algorithm over conventional look-up table methods. We implement the algorithm on a GPU, and report a speedup factor of over 30. We show that this transform is superior over wavelet-based approaches, and show quantitative and qualitative improvements over the state-of-the-art WASABI method; we report accuracy gains of 2dB PSNR, as well improved view preservation.