A method for high-speed three-dimensional measurement with low-speed camera is proposed. The spatial frequency encoded fringes are projected with high frame rate and deformed fringes are captured with low frame rate. Several fringes are integrated in one captured image. The directions and/or frequencies of these fringes are different. The spatial frequency spectrum of these fringes is separate in spatial frequency domain. So, the phases of different fringes can be obtained by filtering the image with different filters. Then several 3D shapes of different time are obtained from one captured image. The experiments are carried out to verify proposed method and measurement results are demonstrated. The method improves the speed of 3D shape measurement and reduces the cost of measurement system as well.
Proc. SPIE. 6832, Holography and Diffractive Optics III
KEYWORDS: Fringe analysis, Holograms, Holography, 3D image reconstruction, Digital holography, Digital imaging, Near field diffraction, Charge-coupled devices, Reconstruction algorithms, 3D image processing
The reconstruction of digital hologram is a key topic in the research of digital holography, which is maturely
developed for the reconstruction of two-dimensional image. Recently, the reconstruction of three-dimensional
image has attracted much more attention. In this paper, we apply the two-wavelength digital holographic
contouring method to obtain the three-dimensional image, the basic idea of which is to reconstruct the shape
through the phase difference that can be numerically calculated by Fresnel diffraction algorithm. Considering
the fact that the obtained phase is wrapped on the interval (-π, π], and the unwrap algorithm always fails for
the object with large height steps or spatially isolated areas, we adopt the two-wavelength digital holography to
provide an equivalent longer wavelength such that the obtained phase is continuous everywhere. The experiment
results prove the feasibility and efficiency of the method.
A fundamental problem in optical and digital holography is the existence of speckle noise in the reconstructed image.
Many approaches have been carried out in order to overcome this problem. In this paper a new technique to reduce the
speckle noise is proposed based on the physical nature of speckle noise. The illumination direction of the object beam is
changed to provide a different phase information for the same recorded object in an off-axis digital holographic setup
and the holograms are recorded with different illumination directions. Then the intensity information of the reconstructed
images is superposed and averaged to reduce the speckle noise. The theoretical analysis and experimental results are
shown to valid our proposal. They prove that the technique can effectively reduce the speckle noise without ruining the
In this paper, we introduce the potentialities of the digital hologram for the three-dimensional shape measurement from
numerical reconstructed image. The image processing of the Fresnel digital hologram recorded by CCD sensor and the
algorithm for 3d shape reconstruction is taken into account. Firstly, we stitch a series of small digital holograms to obtain a
hologram with larger size. Secondly, the reconstructed image sequences of different depth planes are obtained by
numerical reconstructing hologram. Finally, the depth information of each sample point of object is gained by algorithm of
focus measure evaluation, in which the maximum focus measure of a region is found by the grey level variance of image
sequence. The basic principle of this technique and its experimental verification are presented.
In this paper, a new method, which synthesizes the technology of computer graphics (CG) and holographic integral
photography, is proposed to realize the holographic display of virtual 3D scene in large size. In this method, elemental
stereographic images of 3D scene are computed by a virtual holocoder instead of using pickup process. And then, the
color of elemental stereographic images is separated by computer and three tricolor elemental image series are printed by
high graphics printer. The printed image series can be integrated into the previous 3D scene with a lens array whose
optic parameters match to the virtual holocoder. If the image series are illuminated by laser, the virtual 3D scene is
reconstructed by coherent light, and then the reconstructed scene can be recorded by single wavelength color holographic
technology in large size.
Large amounts of communication bandwidth and memory space is occupied to transmit and store digital hologram on
account of its enormous data volume. It is necessary to compress the information of digital hologram for effective
transmittance and storage. After theory of off-axis hologram is studied, it is found that at most half of the information is
useful for reconstructing image. A new method is proposed to compress the information, according to the spectrum
character of off-axis hologram. The sampling frequency is reduced by shifting the useful information of digital hologram
from high-frequency section to low-frequency section. Therefore, the information is compressed. The detailed procedure
is expressed as follows. (1) To filter the hologram with a high-pass filter, whose cut off frequency is equal to the
difference between frequency of reference beam and the highest frequency of object beam. (2) To multiply every row of
the filtered hologram by a cosine sequence, whose frequency is equal to the difference between frequency of reference
beam and the highest frequency of object beam. (3) To filter the processed hologram with a low-pass filter. (4) To
subsample the hologram with a sampling frequency as four times as the highest frequency of the object. As thus, the
digital hologram is compressed to half size of the original one at least. Moreover, higher compression rate will be
obtained if the subsampled hologram is compressed with other methods. The theoretical analysis and experimental
results are presented.
A new technique is proposed to obtain a real color hologram with a large viewing angle by the combination of computer
and optical method. Two steps are followed to finish this technique. (1) Computer-generated hologram H1 is yielded.
According to the theory of light propagation, and taking full advantage of computer-generated hologram, object
lightwave distribution of three monochromatic Fresnel holograms with a large dimension is computed in different area of
the same plane. Object lightwave distribution is folded into smaller area based on the method of mirror images. High
density holograms H1r, H1g, H1b are generated after the holograms are exported and microfilmed. (2) A rainbow
hologram H2 is generated by optical ways. In the recording procedure, two parallel mirrors with appropriate parameters
must be matched in the experiment system. In terms of the reversibility of light path principle, an image with a wide
viewing angle is reconstructed by reversing the reconstruction lightwave. The principle of the proposed method and the
experimental result prove that the technique achieves a color reconstructed image with a wide viewing angle of 14° . It is
very clear that the stereoscopic effect of the reconstructed image is increased.
Based on the Arrayed Waveguide Grating (AWG) equation and output light intensity equation, dual peaks electro-optical
AWG is presented, whose properties are analyzed in details in the paper. The experiments for the electro-optical dual
peaks AWG are simulated by Optiwave software, and the experimental results verify the theory very well.
Two novel content meters for liquid refractive index or concentration measurement are proposed based on the simple reflex fiber optic sensor configurations. One sensor exploits a reflex and concentrically arranged fiber probe structure which is very similar to the traditional intensity-modulated fiber optic displacement sensors, but the light captured by receiving fibers is modulated by the varied solute concentration, being in proportion to the liquid refractive index, instead of displacement. The other sensor works based on detecting the edge shift of the reflected light spot, which is modulated by the refractive index variation of the liquid. Theoretical analysis and simulations are carried out with the measurement range of refractive index from 1.0 to 1.5.
Water content measurement technologies are very important for quality inspection of food, medicine products, chemical products and many other industry fields. In recent years, requests for accurate low-water-content measurement in liquid are more and more exigent, and great interests have been shown from the research and experimental work. With the development and advancement of modern production and control technologies, more accurate water content technology is needed. In this paper, a novel experimental setup based on near-infrared (NIR) spectral technology and fiber-optic sensor (OFS) is presented. It has a good measurement accuracy about ∓ 0.01%, which is better, to our knowledge, than most other methods published until now. It has a high measurement resolution of 0.001% in the measurement range from zero to 0.05% for water-in-alcohol measurement, and the water-in-oil measurement is carried out as well. In addition, the advantages of this method also include pollution-free to the measured liquid, fast measurement and so on.
In this paper, we propose a technique to reconstruct 3-D object shape by its measurement data using CGH. Firstly, both the range image and the intensity image of 3D object are acquired simultaneously using 3D shape measurement system. Then, the Fresnel CGH is designed and fabricated using these data. Finally, combining CGH with optical holography, an image hologram is recorded. The principle of the proposed method, the technology for designing and fabrication of the CGH and optical hologram, and the experimental results are also given in this paper.