Computational holography is one of the most potential 3D display technologies. In recent years, with the continuous iterative evolution of holographic optical theory and the continuous maturity of computer software and hardware technologies, related technologies have developed rapidly. Correlation optimization algorithm is a research hotspot at present. This paper studies and analyzes several pure phase hologram generation and optimization algorithms commonly used in this field in recent years, and points out that the above algorithms have the limitation that the quality of reconstructed images cannot be further effectively improved; for this problem, we propose a new optimization idea based on high-dimensional space is to find the reconstructed image with similar pixel distribution to the target image in the highdimensional space. At the same time, we propose a more practical pixel correction method, which considers the reconstruction of the image from the high-dimensional space. Optimization can further effectively reduce interference such as speckle noise and improve the quality of reconstructed images. Through experimental calculation, we obtained the peak signal-to-noise ratio and structural similarity of the reconstructed image before and after the correction of the common algorithm and the original image and compared them. It can be verified through experiments that the numerical improvement of the above two indicators obtained by our proposed method is obvious. The quality of the reconstructed images has also been better improved.
In this paper, the principle as well as the implementation of EPISM method are introduced firstly. In order to evaluate the reconstruction quality better, the imaging process of EPISM based holographic stereogram is regarded as a general optical system imaging, and modeling and optimization of EPISM method are proposed from two different aspects of angular spectrum and spatial domain. In the analysis of angle spectrum theory, the exit pupil function model is simplified firstly and the optical transfer function (OTF) with defocusing aberrations was established. In spatial domain analysis, the modulation characteristics of the hogel based holographic stereogram is constructed and validated while a diffraction-limited imaging model of the hogel based holographic stereogram is established, and the effective resolvable size of the reconstructed image point is simulated. The theories show that there is an optimal hogel size existed for the certain depth of scene. Optical experiments demonstrate the validity of our analysis, and the optimized parameters of hogel sizes can improve the imaging quality of full parallax holographic stereogram effectively.
In this paper, image processing technology is used to simulate the reconstructed images of holographic stereogram in different depth planes. The quality of the reconstructed image of a single hogel at different depths is analyzed firstly. The size of the hogel, the distance between the holographic stereogram and the LCD and the distance between the holographic stereogram and the imaging plane are all factors affecting the quality of the reconstructed image. By dividing the hogel into many sub-parts, the reconstructed images of each sub-parts are analyzed one by one, and by superimposing the reconstructed images of each sub-parts, the reconstructed images of the hogel at different depths can be obtained. Then, the relationship between the reconstructed images of each hogel is analyzed, and the reconstructed images of all hogels are translated and superimposed to obtain the reconstructed images of the holographic stereogram in different depth. The synthetic parallax images generated by using the effective perspective image segmentation and mosaicking (EPISM) algorithm proposed by our group are used to print the holographic stereogram. The experiment results show that the reconstructed images of the stereogram in different depth planes are consistent with the simulation results, which verifies the validation of the simulation.
KEYWORDS: 3D displays, 3D image processing, Integral imaging, Display technology, Image processing, Displays, Cameras, 3D modeling, 3D vision, Visualization
Traditional visual images can only be used as flat display to convey two-dimensional (2D) information, which is difficult to meet needs of people. Integral Imaging (InI) is a kind of three-dimensional (3D) display technology using computer graphics, image processing and other display technologies. With the continuous optimization of algorithms and the growth accuracy of devices such as display devices, InI has shown unique advantages in equipment production, military sciences, medical insurance, commercial advertising and more. This article focuses on the advantages and applications of 3D InI technology.
KEYWORDS: 3D image processing, Integral imaging, 3D image reconstruction, Microlens array, Image processing, 3D displays, Image resolution, Imaging systems, Image quality, Computing systems
Integral imaging technology would be one of the most promising technology for the battlefield visualization in future war. The reconstruction of integral imaging can be classified into optical reconstruction and computational reconstruction. Computational reconstruction is accomplished by computer simulation of the optical integral imaging reconstruction process, which can overcome many problems caused by device limitation in optical integral imaging system and improve the image quality through digital processing technology. The reconstructed image is digital format, which can provide data support for 3D depth extraction, 3D target recognition, 3D image processing and so on. Based on the principle of integral imaging, this paper focuses on the principle and development history of computational reconstruction, and compares the performance of two computational reconstruction methods.
A spatial frequency index method is proposed to cull the occlusion in computer generated hologram. The object points with the same spatial frequency are put into a set, and only the point closest to the hologram is contributed to the hologram because of their mutual occlusion. The phases of corresponded spatial frequency are precomputed and stored in a table. The phases on the hologram are obtained from the table according to the spatial frequency of object point. Experiments are performed and the results demonstrate that the proposed method can cull the hidden surfaces of 3-D scene correctly. The occlusion effect can be well reproduced along with the speeding up of the calculation.
KEYWORDS: 3D displays, Integral imaging, Spatial resolution, LCDs, 3D image processing, 3D modeling, Image resolution, Imaging arrays, Cameras, Holography
Integral imaging is known as a promising 3D display method for its ability to reconstruct the light field of the scene. However, integral imaging suffers from low spatial resolution and narrow viewing angle due to the limited spatial bandwidth product of LCD, which prevents its commercial application. In conventional integral imaging display, spatial resolution and viewing angle are two vital factors that should be considered, and many previous research focuses on the two factors. A novel integral imaging 3D display system with large viewing angle about 35° and high spatial resolution for HVS is presented. The method is composed of a high definition 5K LCD panel, a macro lens array and a light shaping diffusor. One point of the method different from conventional integral imaging in which micro lens array is used, a macro lens array with elemental lens diameter 1cm is employed in our method to ensure a large viewing angle, however, this may result in low spatial resolution for HVS. And the other point is a light shaping diffusor is placed in front of the lens array with proper distance, and lifelike 3D reconstruction is obtained. Experimental results with full parallax, large viewing angle and high resolution 3D images are shown to verify the validity of the proposed system.
A spatial frequency sampling look-up table method is proposed to generate a hologram. The three-dimensional (3-D) scene is sampled as several intensity images by computer rendering. Each object point on the rendered images has a defined spatial frequency. The basis terms for calculating fringe patterns are precomputed and stored in a table to improve the calculation speed. Both numerical simulations and optical experiments are performed. The results show that the proposed approach can easily realize color reconstructions of a 3-D scene with a low computation cost. The occlusion effects and depth information are all provided accurately.
Holographic stereogram display technology is one of the research focuses in three-dimensional (3D) holographic display. Holographic stereogram is essentially to infinitely approach the true 3D object using a sequence of 2D perspective images. In this paper, several holographic printing methods are summarized firstly, including two-steps transfer hologram printing technique, horizontal parallax only (HPO) stereogram with laser direct writing and holographic elements based full-parallax holographic stereogram method. Also the principles of printing, method of recording, and the various factors that affect the printing quality of the holographic stereogram are discussed and analyzed in detail. Then, after designing the matching relationship between full-parallax holographic stereogram and holographic elements, a new method to print holographic stereogram is proposed. With this method, image distortions can be decreased to improve the printing quality because this method has less impact factors and easier operations in experiment. Finally, it points out the recent development state of holographic stereogram.
Based on Gaussian mixture model, an improved detection algorithm, which aimed at updating the real-time character and accuracy of the moving target detection in intelligent video surveillance systems effectively, is elaborated in this paper. It combines the advantages of GMM and improved maximum between class variance method. The algorithm not only improves the speed of detecting targets in the intelligent systems, but also solves the inherent problems efficiently in poor real-time performance and error detection problem. In conclusion, the experiment results demonstrated that the algorithm has an excellent adaptability and anti-interference performance to fit the complicated situation and changing environment.
An improved parallel algorithm for holograms of three-dimensional objects was presented. According to the physical characteristics and mathematical properties of the original ray tracing algorithm for computer generated holograms (CGH), using transform approximation and numerical analysis methods, we extract parts of ray tracing algorithm which satisfy parallelization features and implement them on graphics processing unit (GPU). Meanwhile, through proper design of parallel numerical procedure, we did parallel programming to the two-dimensional slices of three-dimensional object with CUDA. According to the experiments, an effective method of dealing with occlusion problem in ray tracing is proposed, as well as generating the holograms of 3D objects with additive property. Our results indicate that the improved algorithm can effectively shorten the computing time. Due to the different sizes of spatial object points and hologram pixels, the speed has increased 20 to 70 times comparing with original ray tracing algorithm.
A pure phase-modulated computer-generated hologram (CGH) method is presented to generate a full parallax holographic stereogram. The holographic stereogram plane is divided into several two-dimensional holographic elements (hogels). The spectra of the hogels are rendered from multiview full parallax images of three-dimensional (3-D) objects. The phase-modulated hogel is calculated by iterative Fourier transform algorithms to improve diffraction efficiency and eliminate conjugate images. A gray calibration technique is introduced to generate the accurate intensity modulation of pure phase hogels. The holographic stereogram that we proposed is reconstructed by an optical system based on a phase only spatial light modulator. The experimental results demonstrate that our proposed method can successfully reconstruct parallax images of 3-D objects.
The vergence-accommodation conflict in holographic stereograms is investigated. The visual distortion and fatigue caused by the conflict are analyzed. A method for generating full-parallax holographic stereograms without vergence-accommodation conflicts is proposed. Two-dimensional spatial and spectral samplings are carried out on both the hologram and the reconstructed planes. The depth cues of three-dimensional object points are introduced in the iterative process of calculating subholograms with different spectral components. The stereogram is a combination of holographic elements (hogels), and each hogel is formed by performing a weighted summation of subholograms, where parallax images and depth information are used to select the constituent subholograms. A proof-of-principle experiment is carried out in an optical system based on a spatial light modulator. The results show that the improved full-parallax holographic stereogram can control the focusing depths of points and guarantee consistency between the vergence and accommodation distances. The influence of the size of the hogels on holographic imaging quality is also investigated.
A phase-searching look-up table (PS-LUT) method is proposed to dramatically reduce the memory size of the new look-up table (N-LUT) method as well as to keep its advantage of fast computational speed. Small quantities of samples are chosen as the basic phase points (BPPs) in the principle fringe pattern (PFP), and phases of the object points for BPPs are precalculated and stored in the table. The phases of object point for the whole PFP could be quickly obtained through a phase-searching method. With proper reference beam phases, PFP could be rapidly generated. The experimental results reveal that the computational speed of the proposed method is about 24 times faster than that of the ray-tracing method, and the required memory size is 1731 times less than that of the N-LUT method. To eliminate the coherent noise of the N-LUT and PS-LUT, the random PFP N-LUT (RN-LUT) and PS-LUT (RPS-LUT), in which the PFP is randomly chosen for every object point, are put forward. The reconstructed images with a spatial light modulator indicate that both the RN-LUT and RPS-LUT methods are extremely effective in improving the quality of the reconstructed images.
Based on the existed ways of 2-D reconstructed images by spatial light modulator (SLM), the methods to enhance the reconstructed quality of 3-D images are investigated in this paper. Based on the diffraction theory, the effects of a lattice SLM with a limited fill factor on the reconstructed images are analyzed. Through adding the phase of the convergent spherical wave, the two focused planes of reconstructed images and the multi-order beams caused by the lattice structure of the SLM can be separated spatially. Therefore, the spatial filter is used to eliminate the influences of higher-orders diffraction beams and zero-order light of reconstructed images, respectively. A holographic optoelectronic display system based on liquid crystal spatial light modulator (LC-SLM) is set up to demonstrate this method.
A dual-channel fusion system of visual and infrared images based on color transfer The increasing availability and deployment of imaging sensors operating in multiple spectrums has led to a large research effort in image fusion, resulting in a plethora of pixel-level image fusion algorithms. However, most of these algorithms have gray or false color fusion results which are not adapt to human vision. Transfer color from a day-time reference image to get natural color fusion result is an effective way to solve this problem, but the computation cost of color transfer is expensive and can’t meet the request of real-time image processing. We developed a dual-channel infrared and visual images fusion system based on TMS320DM642 digital signal processing chip. The system is divided into image acquisition and registration unit, image fusion processing unit, system control unit and image fusion result out-put unit. The image registration of dual-channel images is realized by combining hardware and software methods in the system. False color image fusion algorithm in RGB color space is used to get R-G fused image, then the system chooses a reference image to transfer color to the fusion result. A color lookup table based on statistical properties of images is proposed to solve the complexity computation problem in color transfer. The mapping calculation between the standard lookup table and the improved color lookup table is simple and only once for a fixed scene. The real-time fusion and natural colorization of infrared and visual images are realized by this system. The experimental result shows that the color-transferred images have a natural color perception to human eyes, and can highlight the targets effectively with clear background details. Human observers with this system will be able to interpret the image better and faster, thereby improving situational awareness and reducing target detection time.
KEYWORDS: 3D displays, Holography, Diffraction, Holograms, Digital holography, Computer generated holography, Diffraction gratings, Photonics, 3D image processing, 3D modeling
Holographic display is a true three-dimensional (3D) display technology presenting all depth cues without using any
special glasses. With this technology we have developed a system of city photonics map. In the system there are three
key steps: gaining raw 3D point clouds data, Computer-generated holograms, and digital holographic display of 3D data.
In the first step, the theory of structure from motion (SfM) is applied. Then an algorithm of phase CGH with inverse
diffraction is proposed and implemented. Difference from ordinary CGH is that the diffraction fringes of 3D
reconstructed terrain data are obtained from the diffraction results by the reverse strike means. At last, 3D hologram is
displayed on the developing experimental platform and printed on the holographic silver halide plate.
KEYWORDS: Computer generated holography, 3D image reconstruction, 3D image processing, Diffraction, Reconstruction algorithms, 3D acquisition, Image processing, Near field diffraction, Spatial light modulators, Modulation
A novel method for computing kinoform of 3D object based on traditional iterate Fourier transform algorithm(IFTA) is proposed in this paper. Kinoform is a special kind of computer-generated holograms (CGH),which has very high diffraction efficiency since it only modulates the phase of illuminated light and doesn’t have cross-interference from conjugate image. The traditional IFTA arithmetic assumes that reconstruction image is in infinity area(Fraunhofer diffraction region), and ignores the deepness of 3D object ,so it can only calculate two-dimensional kinoform. The proposed algorithm in this paper divides three-dimensional object into several object planes in deepness and treat every object plane as a target image,then iterate computation is carried out between one input plane(kinoform) and multi-output planes(reconstruction images) .A space phase factor is added into iterate process to represent depth characters of 3D object, then reconstruction images is in Fresnel diffraction region. Optics reconstructed experiment of kinoform computed by this method is realized based on Liquid Crystals on Silicon (LCoS) Spatial Light Modulator(SLM). Mean Square Error(MSE) and Structure Similarity(SSIM) between original and reconstruction image is used to evaluate this method. The experimental result shows that this algorithm speed is fast and the result kinoform can reconstruct the object in different plane with high precision under the illumination of plane wave. The reconstruction images provide space sense of three-dimensional visual effect. At last, the influence of space and shelter between different object planes to reconstruction image is also discussed in the experiment.
In the use of crystalline silicon solar cells, the micro defects, such as cracks, the grain boundary dislocation, broken
metal grid fingers, etc., will seriously affect the efficiency and the life of crystalline silicon solar cells. Therefore, it is
necessary to detect the micro defects of Si solar cells rapidly and accurately in the production process. In this paper,
firstly, the relationship between the electroluminescence (EL) intensity from Si solar cells under the forward bias and
minority carrier diffusion length is simulated based on the calculation under the condition of ideal P-N junction model.
There exists one to one quantitative agreement. We find that the relationship referred above is nonlinear. Secondly, the
relationship between the defects in Si solar cells and minority carrier diffusion length (EL intensity) is summed up. The
defects and minority carrier lifetime are also in accord with this relationship. Based upon these, the micro defects in Si
solar cells could be made out in theory. With experiments, the defects in c-Si solar cells and poly-Si solar cells are
detected clearly from EI images. Theory analysis and experiments show that the method is reasonable and efficient.
As a result of unexpected attitude variation or random shaking of the camera carrier, the image sequences would become
blurred and instable. High performance stabilization platform adopting precise gyros is usually dear and complex.
Electronic image stabilization technique is cheap and low power dissipation, but the intricacy of algorithm substantial
increase considering camera intentional motion and moving objects existing in the video. It is difficult to be satisfied
with both precision and real-time aspect simultaneously. Design a cheap stabilization platform using a small MEMS
IMU, limiting the range of variation of the camera attitude, and avoiding scene sphere observed instantaneous severe
change; the perspective collineation from three-dimensional space to two-dimensional image plane is analyzed, and pixel
coordinate conversion model related to the camera attitude variation is deduced and simplified. Then utilizing the IMU
signal to compensate the frame rotation, and realizing stable video output.
MEMS gyro is used in inertial measuring fields more and more widely, but random drift is considered as an important
error restricting the precision of it. Establishing the proper models closed to actual state of movement and random drift,
and designing a kind of effective filter are available to enhance the precision of the MEMS gyro. The dynamic model of
angle movement is studied, the ARMA model describing random drift is established based on time series analysis
method, and a modified self-adapted Kalman filter is designed for the signal processing. Finally, the random drift is
distinguished and analyzed clearly by Allan variance. It is included that the above method can effectively eliminate the
random drift and improve the precision of MEMS gyro.
This paper introduces a new medical X-ray diagnostic imaging method: direct radiography (DR), which will resolve digitalization problem of conventional X-ray medical imaging, and may replace film imaging in the future. In our developed DR system, a high resolution amorphous Silicon (a-Si) image sensor is used which can acquire 1920*1536*12bits image in 1.6 seconds in its fastest imaging speed. The software of the system including DR image acquisition workstation and DR image post-process workstation can not only acquire, correct and store the images, but also can manage the DR images in network database. In the paper, the mechanism of DR imaging, the composition of the developed DR system, the advantages of DR imaging over traditional X-ray medical imaging are described, and DR imaging results of the developed system are shown at last.
A multispectral image fusion problem within the wavelet coefficient space has been studied in the present paper. In this algorithm, several kinds of area-based feature selection operators have been designed to select the image features in levels of the wavelet transform pyramids of source images. The problem of multiscale image enhancement and image fusion of different resolution has also been studied in the paper.
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