Color holography using the angular selectivity of volume recording media

A display hologram of an object can be recorded and reconstructed in three primary colors if the angular selectivity of volume recording media is exploited. Three holograms are recorded in the same medium, each at a different primary color. These three holograms are reconstructed by simultaneous illumination of the hologram with the original reference beams. By proper choice of the angles that the reference beams make to the hologram, it is possible to suppress strongly cross talk between the different reconstructions (e.g., the red object reconstruction in green light). The technique exhibits high resolution, high diffraction efficiency, and vivid colors. Through the addition of three holographically recorded volume gratings it is possible to reconstruct the hologram with a beam of white light. The saturation and brightness of each primary color in the reconstruction can be adjusted by selection of an appropriate thickness for the corresponding grating.     

Computer generated holograms from three dimensional meshes using an analytic light transport model

We present a method to analytically compute the light distribution of triangles directly in frequency space. This allows for fast evaluation, shading, and propagation of light from 3D mesh objects using angular spectrum methods. The algorithm complexity is only dependent on the hologram resolution and the polygon count of the 3D model. In contrast to other polygon based computer generated holography methods we do not need to perform a Fourier transform per surface. The theory behind the approach is derived, and a suitable algorithm to compute a digital hologram from a general triangle mesh is presented. We review some first results rendered on a spatial-light-modulator-based display by our proof-of-concept software.     

Real-time three-dimensional object reconstruction by use of a phase-encoded digital hologram

A three-dimensional (3D) object reconstruction technique that uses only phase information of a phase-shifting digital hologram and a phase-only spatial-light modulator is proposed. It is well known that a digital hologram can store both amplitude and phase information of an optical electric field and can reconstruct the original 3D object in a computer. We demonstrate that it is possible to reconstruct optically 3D objects using only phase information of the optical field calculated from phase-shifting digital holograms. The use of phase-only information enables us to reduce the amount of data in the digital hologram and reconstruct optically the 3D objects using a liquid-crystal spatial light modulator without optical power loss. Numerical evaluation of the reconstructed 3D object is presented.     

Computer-generated holograms of a real three-dimensional object based on stereoscopic video images

A novel method of using stereoscopic video images to synthesize the computer-generated hologram (CGH) patterns of a real 3D object is proposed. Stereoscopic video images of a real 3D object are captured by a 3D camera system. Disparity maps between the captured stereo image pairs are estimated and from these estimated maps the depth data for each pixel of the object can be extracted on a frame basis. By using these depth data and original color images, hologram patterns of a real object can be computationally generated. In experiments, stereoscopic video images of a real 3D object, a wooden rhinoceros doll, are captured by using the Wasol 3D adapter system and its depth data are extracted from them. Then, CGH patterns of 1280 pixels x 1024 pixels are generated with these depth-annotated images of the wooden rhinoceros doll, and the CGH patterns are experimentally displayed via a holographic display system.     

真彩色动感全息图

提出了用单色激光器制作真彩色动感全息图的方法。该方法用三色光栅相机将景物的彩色信息记录在一张透明片上,并使用散射参光法一次曝光合成一幅真彩色全息图。对从不同观察角度所拍摄的透明片进行多次全息曝光并记录在同一张全息片上,可在普通白炽灯下看到景物的真彩色动感全息像。采用散射光作为参考光记录全息片,大大降低了相干噪声。一次曝光记录一幅真彩色全息图,不仅使透明片数量和曝光次数减少为分色记录的1／3,而且消除了由分色记录三次曝光所带来的颜色分离,增加了彩色像的真实感和清晰度。     

Color holography to produce highly realistic three-dimensional images

The 1964 publication by Emmett Leith and Juris Upatnieks [J. Opt. Soc. Am. 54, 1295 (1964)] introduced the possibility of using holograms to record three-dimensional (3D) objects. Since then, there has been an interest in creating display holograms, i.e., holograms primarily produced to show objects in 3D. More recently, full color holography has become a reality, which was predicted in the 1964 paper. To record a hologram in which both the 3D shape and the color of the object are accurately reproduced, at least three laser wavelengths are needed. By computer simulation of the holographic color rendering process, the required amount of laser wavelengths and their distribution within the visible electromagnetic spectrum have been investigated. The quality of a color hologram also depends on the properties of the recording material. The demand on a panchromatic material for color holography is described. Recording techniques for color holograms are presented as well as the future of color holography as the perfect 3D imaging technique.     

Secure three-dimensional data transmission and display

An optical three-dimensional (3D) display system interfaced with digital data transmission is proposed. In this system, an original 3D object is encrypted by use of a random phase mask and then the encrypted pattern is recorded as a digital hologram. The digital hologram key is also recorded for optical decryption. Both the encrypted digital hologram and the digital hologram key are transmitted to a receiver through a conventional communication data channel. At the receiver, the 3D scene is reconstructed and displayed optically in a retrieval system based on a joint-transform correlation. Experimental results are presented. We investigate the influence of quantization of the joint power spectrum in the optical correlator on the quality of the reconstructed image.     

The self-imaging effect in lensless holographic microscopy and its application in characterising periodic structures

A lensless holographic microscope was used to record a hologram of self-organised monolayers of micron-sized polystyrene spheres. By reconstructing the hologram digitally using a computer it was found that the original periodicity of the object produces planes of identical images, as well as planes that show reversed contrast images at separations predicted by the first-order approximation to the Talbot theory of the self-imaging effect. The performance of a compound light microscope is compared and contrasted with that of the holographic system, specifically examining the ability of the different systems to recover the distribution at the Talbot planes and to characterise properties of periodic structures. A theoretical model is developed and experimental results are presented.     

Three-dimensional matching by use of phase-only holographic information and the Wigner distribution

Matching of three-dimensional (3-D) objects is achieved by Wigner analysis of the correlation pattern between the phase-only holographic information of a reference object and that of a target object. First, holographic information on the reference object and on the target object is extracted by use of optical scanning holography as a form of electrical signal. This electrical information is then stored in a computer for digital processing. In the digital computer, the correlation between the phase-only information of the hologram of the reference object and that of the target object is calculated and analyzed by use of a Wigner distribution. The Wigner distribution yields a space-frequency map of the correlation pattern that indicates whether the 3-D image of the target object matches that of the reference object. When the 3-D image of the target object matches that of the reference object, the Wigner distribution gives a well-defined line that directly indicates the 3-D location of the matched target object. Optical experiments with digital processing are described to demonstrate the proposed matching technique.     

基于SPD的物体色快速分光测试系统设计

根据光度学与色度学理论，采用国际照明委员会（CIE）推荐的d/8标准照明／观察几何条件，应用自扫描光电二极管阵列（SPD）作为乐电探测器，设计了由积分球，脉冲光源，多色仪，光电放大与A／D转换器以及专用计算机等部分组成的双光路多通道物体表面色全光谱快速测试系统，该系统单次测色周期小于1秒，对陶瓷白板的测量精度（色度坐标）优于0．0003，重复性达到0．0001，满足了快速又准确的分光测色要求。     

胶印配色光学常数求解方法优化

建立计算机配色数据库时,基墨色调阶梯选取不当易导致配色光学常数求解不准确,进而影响配色效率、颜色预测精度。为构建基于K-M单常数理论配色模型的基墨数据库,分析基墨混合样本配比与吸收散射比之间的关系,提出一阶导色调阶梯法、误差排序色调阶梯法求解光学常数。测试结果表明：将基墨混合样本配比个数缩减至6个时,一阶导及误差排序两种色调阶梯法的颜色预测精度的最大光谱误差为0.0137,最大色差为1.73。     

一种基于 Contourlet 变换的彩色图像全息水印算法

提出了一种结合了全息水印加密技术和 Contourlet 变换技术的彩色图像水印算法。 算法首先将 RGB 模式的水印载体图像转换至 YCrCb 颜色空间,选取亮度分量作为水印载体通道,对其进行多层 Contourlet 分解,得到细节子带图像;而后对二值水印图像进行傅里叶全息加密,将加密后的图像嵌入至载体图像的 Contourlet变换系数中。 仿真实验结果表明,该水印算法具有良好的不可见性,对于常见的几何变换及多种攻击具有良好的鲁棒性。     

浅色墨映射算法研究

针对多色喷墨打印机中常见的Lk与K,Lc与C,Lm与M三类浅原色组合,分别采用色度匹配与密度匹配两种方法,建立了浅色墨与原色墨之间的映射关系,并对两种方法进行了对比,分析了其各自优缺点与适用范围。     

Accelerated algorithm for three-dimensional computer generated hologram based on the ray-tracing method

An accelerated algorithm for three-dimensional computer generated holograms (CGHs) based on the ray-tracing method is proposed. The complex amplitude distribution from the center point of an object is calculated in advance and the field distributions of rest points on the hologram plane can be given by doing a small translation and an aberration to the pre-calculated field. A static two-dimensional car, a three-dimensional teapot, and a dynamic three-dimensional rotating teapot are reconstructed from CGHs calculated with the accelerated algorithm to prove its validity. The simulation results demonstrate that the accelerated algorithm is eight times faster than the conventional ray-tracing algorithm.     

Three-dimensional display of a horizontal-parallax-only hologram

We propose a three-dimensional (3D) holographic display by converting an optically recorded complex full-parallax (FP) hologram to an off-axis horizontal-parallax-only (HPO) hologram. First, we record the complex FP hologram of an object using optical scanning holography. We then convert the complex FP hologram to an off-axis HPO hologram through fringe-matched Gaussian low-pass filtering and with the introduction of an off-axis reference. Finally, we reconstruct the off-axis HPO hologram optically using an amplitude-only spatial light modulator. Until now, only computer-generated HPO holograms have been displayed optically. To the best of our knowledge, this is the first demonstration of a 3D display of an optically recorded HPO hologram.     

Improving the performance of computer color matching procedures

A premise was set up entailing the possibility of a synergistical combination of advantages of spectrophotometric and colorimetric matching procedures. Attempts were therefore made to test the performances of fifteen matching procedures, all based on the Kubelka-Munk theory, including two procedures utilizing the fundamental color stimulus R(FCS) of the spectral decomposition theory. Color differences CIE DeltaE(00) as well as concentration differences DeltaC(AVE) were used to theoretically rank the fifteen color matching procedures. Results showed that procedures based on R(FCS) were superior in accurately predicting colors and concentrations. Additionally, the metameric black component R(MB) of the decomposition theory also showed promise in predicting degrees of metamerism. This preliminary study, therefore, provides evidence for the premise of this investigation.     

Recurrence formulas for fast creation of synthetic three-dimensional holograms

A method for accelerating the synthesis of computer-generated three-dimensional (3-D) holograms, based on conventional ray tracing, is proposed. In ray tracing, computers expend almost all of their resources in calculating the 3-D distances between each one of the point sources composing an object and a sampling point on the hologram. We present recurrence formulas that precisely compute the distances and reduce the computation time for synthesizing holograms to one half to one quarter, depending on the processor type. We demonstrate that a full-parallax hologram with an area of 4800 x 4800 pixels, synthesized for a 3-D object containing 966 point sources of light, is computed within 17 min and is optically reconstructed.     

Lensless anamorphic Fourier transform hologram recorded with prism systems

A novel configuration for recording a lensless anamorphic Fourier transform hologram of a given object's light distribution is proposed. The method is based on the use of prism anamorphic optical systems coupled with phase cancellation at the hologram plane. Anamorphic systems with cylindrical lenses and prisms are critically evaluated through computer simulations for their suitability in anamorphic Fourier transform holographic configurations. A complete theoretical analysis and experimental demonstration of the recording and reconstruction of a lensless anamorphic Fourier transform hologram are presented.     

Fast computation for generating CGH of a 3D object by employing connections between layers

An approximate method for generating computer-generated holograms (CGH) of a 3D object with six times faster speed than the conventional algorithm is presented. In the conventional algorithm, a 3D object is sliced into many layers and treated as a collection of self-illuminated point light source. The propagation process of a light ray from every point of an object to all the points on the hologram plane is simulated and interfered with by the reference beam to form a CGH. In our proposed method, under the assumption that the depth of a 3D object is much smaller than the recording distance, we just need to calculate the oblique distance between the first layer and the hologram plane, and then the oblique distances from the other layers to the hologram plane can be obtained from a simple relation, thus the computational time is much reduced. The CGH is optically reconstructed and the quality of the reconstructed image agrees well with that from the conventional algorithm.     

基于CMYK颜色空间的光全息水印算法研究

在印刷CMYK颜色空间、傅里叶全息加密和数字水印理论的基础上,提出了基于CMYK颜色空间的光全息水印算法。该算法不用转换颜色空间,避免了未印刷就人为导致水印信息的丢失,提高了重建水印的相似度;解密时,由于傅里叶变换的特性,重建水印的共轭图像与原水印图像互相叠加,增强了重建水印的清晰度。实验结果表明,该算法有较好的不可见性和较强鲁棒性,可以抵抗一般图像处理等操作。