A new multiple-exposure scheme for full-color full-parallax holographic stereogram

We propose a new multiple-exposure scheme for full-color full-parallax holographic three-dimensional (3D) printer, in which two of three primary-color holograms are exposed at the same location on the recording medium. In this paper, the optimal combinations of colors for multiple exposure are experimentally derived. In addition, it is shown that the proposed method enables higher brightness, better color reproducibility, and high resolution through the experiment of recording and measurement of color-chart holographic stereogram.     

A method of distortion compensation of multiplex holograms

A new method for making distortion-free multiplex holograms is proposed. The original images of them are processed by a computer to cancel the distortion of the final image. Examples of the reconstructed images are also presented.     

3-D distortion of observed images reconstructed from a cylindrical holographic stereogram. (1) laser light reconstruction type

In the case that the image reconstructed from a cylindrical holographic stereogram with laser light reconstruction (LCHS) is observed by binocular vision, the 3-D distortion characteristics of the image are studied. Using an object of a distinctive construction, some examples are calculated and experimental results are also shown, and the optimum condition to synthesize the LCHS is given.     

3-D distortion of observed images reconstructed from a cylindrical holographic stereogram. (2) white light reconstruction type.

The 3-D distortion of the observed images reconstructed from cylindrical holographic stereograms with white light reconstruction (WCHS) are considered, and, from the viewpoint of the distortion, the area of the viewing position is presented.     

Radial tilt compensation method of holographic disk drive

Bragg angle mismatch by tangential and radial tilts is a critical problem in holographic digital data storage. Generally, tangential tilt can be easily compensated for in holographic digital data storage. However, radial tilt is not easily compensated for. In this paper, we propose a new method of radial tilt compensation. The proposed method can compensate for Bragg angle mismatch caused by radial tilt.     

Memory-efficient algorithm for lens distortion compensation

Distortion introduced by a lens in a measurement system based on an image sensor usually must be compensated. The memory used for distortion compensation by a lookup table is proportional to the image sensor size. To reduce the memory usage, a compression algorithm is proposed and implemented.     

Reconstruction resolution enhancement of EPISM based holographic stereogram with hogel spatial multiplexing

We investigate how the splicing mode of a holographic element (hogel) affects the reconstruction of a 3D scene to improve the reconstruction resolution of a holographic stereogram fabricated using the effective perspective image segmentation and mosaicking method (EPISM). First, the effect of hogel spatial multiplexing on holographic recording and reconstruction is studied based on the mechanism of recording interference fringes in the holographic recording medium. Second, combined with the influence of multiple exposures on the hologram's diffraction efficiency, the diffraction efficiency of the holographic stereogram is analyzed in the spatial multiplexing mode. The holographic stereogram is then regarded as a special optical imaging system. The theory of spatial bandwidth product is adopted to describe the comprehensive resolution of the holographic stereogram, which explains why hogel spatial multiplexing can significantly improve the reconstruction resolution of a holographic stereogram. Compared with the traditional printing method under the same parameters in optical experiments, hogel spatial multiplexing has a lower diffraction efficiency but a higher quality of reconstructed image, consistent with the theoretical analysis.     

A method for increasing the sensitivity of determination of the wavefront distortion in optical processing of holographic lateral shear interferograms

A method for obtaining interference patterns of increased sensitivity in optical processing of holographic lateral shear interferograms recorded under linear conditions at a shear exceeding the size of a phase object under study is proposed. Cases of reconstruction of interference patterns of increased sensitivity using matched and optically conjugate holographic lateral shear interferograms are considered. It is shown that two-and fourfold increases in sensitivity, respectively, are obtained in these cases. The validity of the method proposed is confirmed experimentally     

Homography of central points for optical distortion compensation

The paper presents a novel radial lens distortion modelling method for vision systems. It is based on single images of chessboard planar pattern, in which calibration points (corners of chessboard squares) are localised. The points, which are situated near the image centre, where the distortion is negligible, are used to determine undistorted grid of calibration points by the estimation of homographic matrix. The differences in the localisation of undistorted and distorted points are used to find parameters of radial model by the linear least square method. Having the distortion model, the dense compensation is performed with support of bilinear interpolation and a sparse compensation by Newton iterative scheme providing subpixel accuracy.     

Optical compensation of geometrical distortion by a deformable mirror

An optical method for the real time correction of geometrical distortion is reported. It is based on the “fun-house-mirror effect”: An adjustable nonplanar mirror is introduced between object- and pupil-plane and generates a suitable (space-variant) shift of each pixel. The method is restricted to a certain class of distortions, which lead to continuous mirror surfaces (mirror must not break). We also investigate aberrations which are another restriction of the method. Our application was the improvement of TV-systems: before correction 20%, and after correction 50% of pixels had a distortion less or equal than one pixel distance.     

一种图像非线性形变的恢复方法

几何成像系统中非线性形变图像的恢复仍是一个未能很好解决的课题。针对常见的双二次、双三次形变图像,提出了以不完全双二次、双三次插值法拟合形变图像,根据形变的特点采用牛顿迭代法和双线性灰度插值法对图像进行恢复。用所提出的方法对失真图像进行恢复,结果表明,仅选用少量参考点便可得到良好的效果。     

Tomosynthesis: A holographic method for variable depth display

A circular symmetric tomosynthetic arrangement has been investigated using holographic storage techniques. With a set of 24 single radiographs a 3D image of a human orbita region has been generated by image integration leading to a continuously variable depth display of arbitrary layers. The received resolution in a particular layer was about 3 1p/mm. An estimate will be given for the number of necessary radiographs to compare the blurr quality of discrete sample procedures in tomosynthesis with a continuous motion in tomography. Finally a short outline will be given for a possible real-time procedure.     

Display method with compensation of the spatial frequency response of a liquid crystal spatial light modulator for holographic femtosecond laser processing

Liquid crystal spatial light modulators, which are widely used as display devices for computer-generated holograms, have modulation characteristics that depend on spatial frequency. We describe a method for displaying a computer-generated hologram on a liquid crystal spatial light modulator with compensation of its spatial frequency response. Using this method, we demonstrate a binary phase grating with smaller dependence on the spatial frequency. We also demonstrate application of the display method to holographic femtosecond laser processing.     

A holographic method of computing radiation fields

For radiation problems or diffraction at a single frequency, we suggest that the solution can often be expressed in terms of a two-dimensional hologram. The field throughout the three-dimensional volume can then be determined without volume discretisation and without 3D-matrices. The materials and differential equations must be free of non-linearities for the method to be valid.     

A novel coding method for high vividness three-dimensional holographic display

The quality of the reconstructed holographic three-dimensional image is seriously influenced by the noise. A novel encoded algorithm combining the Burch code with the four-step phase shifting method is presented to remove the noise and improve the contrast and resolution of the reconstructed image. The reconstructed three-dimensional images are compared with the results of the median filtering. The performance parameters of two methods are analyzed. The experimental results show that the zero-order light spot, conjugate image and speckle noise are suppressed effectively. The quality of the reconstructed image is noticeably improved.     

Dynamic wave-front distortion compensation with a 134-control-channel submillisecond adaptive system

A 134-control-channel adaptive-optics system consisting of a microelectromechanical mirror array (mu -mirror), a wave-front tilt-control mirror, and a very large scale integration controller utilizing a stochastic gradient-descent optimization of a performance metric is presented. A maximum adaptation rate of ~11, 000 iterations/s was achieved. The system was used to demonstrate real-time compensation for dynamic phase distortions from a laboratory-generated turbulence simulator in a laser-focusing experiment.     

A calibration method of lens distortion for line scan cameras

We present a practical method to calibrate the lens distortion in line scan cameras. The distortion correction software based on this method has been designed and implemented in the digital protection of cultural relics. In this paper, a lens distortion model which applies to line scan cameras is derived from the widely used array camera distortion model. Then, a new calibration method which utilizes the imaging characteristic of equidistant collinear feature points is proposed to calibrate the model. Experiment results show the proposed calibration method is stable and effective.     

Central, auditory mechanisms of perceptual compensation for spectral-envelope distortion.

The spectral envelope is a major determinant of the perceptual identity of many classes of sound including speech. When sounds are transmitted from the source to the listener, the spectral envelope is invariably and diversely distorted, by factors such as room reverberation. Perceptual compensation for spectral-envelope distortion was investigated here. Carrier sounds were distorted by spectral envelope difference filters whose frequency response is the spectral envelope of one vowel minus the spectral envelope of another. The filter /I/ minus /e/ and its inverse were used. Subjects identified a test sound that followed the carrier. The test sound was drawn from an /Itch/ to /etch/ continuum. Perceptual compensation produces a phoneme boundary difference between /I/ minus /e/ and its inverse. Carriers were the phrase "the next word is" spoken by the same (male) speaker as the test sounds, signal-correlated noise derived from this phrase, the same phrase spoken by a female speaker, male and female versions played backwards, and a repeated end-point vowel. The carrier and test were presented to the same ear, to different ears, and from different apparent directions (by varying interaural time delay). The results show that compensation is unlike peripheral phenomena, such as adaptation, and unlike phonetic perceptual phenomena. The evidence favors a central, auditory mechanism.     

Aberrations compensation in holographic high order diffracted wave imaging

This study extends the analysis of image formation and aberrations in holography to that of high order diffracted waves to find a method for compensating the aberrations. The proposed method is able to eliminate all aberrations simultaneously by utilizing special conditions. Experimental results are also presented to support the method.