摘要 :
Measurement of in-plane displacements of a diffuse object by observing the temporal fluctuation of the speckle pattern in a dual-beam illumination speckle interferometer is illustrated. To conceive the temporal changes the object ...
展开
Measurement of in-plane displacements of a diffuse object by observing the temporal fluctuation of the speckle pattern in a dual-beam illumination speckle interferometer is illustrated. To conceive the temporal changes the object is displaced in its plane continuously. A high-speed camera is used to acquire a number of frames of the image of the object motion sequentially. Through Fourier transformation and inverse Fourier transformation of the frames stacked together, the total phase is determined. Finally, the magnitude of the in-plane displacement of the object motion is extracted. The range of displacement that can be measured using this novel method lies between few microns and over 100 mu m on the upper end. Theory together with experimental results are presented in this paper. [References: 8]
收起
摘要 :
The printability of paper is extremely dependent on the topographical properties of the substrate. Imaging instruments make it possible to obtain detailed 3D scans of paper surfaces that can be further used to calculate valuable q...
展开
The printability of paper is extremely dependent on the topographical properties of the substrate. Imaging instruments make it possible to obtain detailed 3D scans of paper surfaces that can be further used to calculate valuable quality predictors. A new imaging instrument, OptiTopo, based on the photometric stereo principle was developed at the Swedish Pulp and Paper Research Institute (STFI) with the advantages of an extreme acquisition speed and the possibility of simultaneously acquiring topographic and reflectance information. The topographical imaging of paper surfaces using this technique has now been investigated and improved. Eleven paper samples covering a wide range of different grades have been analyzed by OptiTopo and their scans compared to those obtained using a reference imaging technique. By applying a suitable signal treatment it is possible to improve the instrument's performance in terms of detail rendering capability. The positive results have been confirmed using visual assessment, classical statistical indicators and frequency analysis. The present limitations of the technique in relation to the physical properties of the substrate are discussed and absolute boundaries for the instrument are proposed.
收起
摘要 :
In fringe projection profilometry, phase shifting (PS) is the most used technique for phase retrieval. However, it suffers from periodicity of sine wave in PS; the result is wrapped into [-pi, pi]; and additional phase unwrapping ...
展开
In fringe projection profilometry, phase shifting (PS) is the most used technique for phase retrieval. However, it suffers from periodicity of sine wave in PS; the result is wrapped into [-pi, pi]; and additional phase unwrapping (PU) is necessary to retrieve the absolute phase. In this paper, a more general technique termed frequency shifting is proposed, based on which the behavior of periodicity is eliminated and absolute phase can be retrieved pixelwisely without any phase unwrapping. The effectiveness of the proposed technique was verified by extensive experimental results, and they demonstrate comparable performance with those of the traditional technique combining PS and PU even in only one step and less projection. (C) 2021 Optical Society of America
收起
摘要 :
We present three-dimensional profilometry based on triangulation in which a hexagonal pattern is projected on the object. To obtain an accurate result with a one-shot photographic image, the Fourier transform method and method of ...
展开
We present three-dimensional profilometry based on triangulation in which a hexagonal pattern is projected on the object. To obtain an accurate result with a one-shot photographic image, the Fourier transform method and method of excess fraction are adopted. The three grating components of the hexagonal pattern are used. For compactness a new pattern projection scheme is introduced. The experimental results show that the constructed optical system works well for measuring the profile of a mannequin with a height resolution of similar to +/- 1 mm. (C) 2008 Optical Society of America.
收起
摘要 :
Two-dimensional Fourier transform profilometry (2- D FTP) for data acquisition of fabric surface shapes is proposed. Phase unwrapping technique based on digital Weighted filter and reliability mask are employed. Ex- Perimental res...
展开
Two-dimensional Fourier transform profilometry (2- D FTP) for data acquisition of fabric surface shapes is proposed. Phase unwrapping technique based on digital Weighted filter and reliability mask are employed. Ex- Perimental results of shape measurement for several fab- Ric appearances are given. From the measured results, it Is shown that this method can make up for not only the Disadvantage of the gray level image analysis which is Only suitable for simple structure and solid-pattern fab- Ric, but also the low speed and high cost of laser dot Scanning technique.
收起
摘要 :
SIM techniques based on synchronous phase shift and vertical scanning have been proposed for fast and precise three-dimensional (3D) measurement. These methods are also named as time-domain phase shift (TSIM) method. In these meth...
展开
SIM techniques based on synchronous phase shift and vertical scanning have been proposed for fast and precise three-dimensional (3D) measurement. These methods are also named as time-domain phase shift (TSIM) method. In these methods, the envelope of light intensity depth response (IDR) curve is extracted to achieve the 3D map. However, when this method is applied in rough surface or complex environment, the imaging noise and background intensity variation will severely affect the shape of IDR which brings difficulties in envelope detection and causes large measurement errors. In this paper, we propose an improved TSIM (ITSIM) technique to enhance the measurement accuracy and robustness of TSIM. In this technique, the modulation distribution of each image is first calculated by a global frequency analysis algorithm, and the modulation depth response curve (MDR) of each pixel can be obtained. These MDR curves are then multiplexed with the corresponding IDR curves to correct the shape of the IDR curves. Finally, the envelope of the corrected IDR curve is detected to accurately reconstruct the 3D shape. The proposed method can effectively resist the intensity fluctuation and imaging noise, and thus can improve the measurement accuracy compared with the conventional TSIM. The experiments performed on standard step sample show that the root mean square error of TSIM and ITSIM is 8.5nm and 21.2nm, respectively, justifying the feasibility of proposed ITSIM.
收起
摘要 :
In white-light interferometry the surface profile is determined by measuring the fringe contrast function of the white-light interferogram. One of the techniques proposed for the measurement of the fringe contrast function is the ...
展开
In white-light interferometry the surface profile is determined by measuring the fringe contrast function of the white-light interferogram. One of the techniques proposed for the measurement of the fringe contrast function is the use of the phase shifting technique with the help of an achromatic phase-shifter. The available phase-shifters employ a rotating polarization component at the output end of the interferometer. Using a rotating polarization component at the input end, rather than at the output end, has certain advantages. In this paper we investigate a rotating half-wave plate phase-shifter at the input end for its applications to a white-light interferometer. [References: 8]
收起
摘要 :
The synthesis of a multiple-peak spatial degree of coherence is demonstrated. This degree of coherence enables us to scan different sample points on different altitudes simultaneously and thus decreases the acquisition time. The m...
展开
The synthesis of a multiple-peak spatial degree of coherence is demonstrated. This degree of coherence enables us to scan different sample points on different altitudes simultaneously and thus decreases the acquisition time. The multipeak degree of coherence is also used for imaging through an absorbing layer with different thicknesses or different indices of refraction along the layer. All our experiments are performed with a quasi-monochromatic light source. Therefore problems of dispersion and inhomogeneous absorption are avoided. Our experimental results are presented. (c) 2005 Optical Society of America.
收起
摘要 :
Intensity saturation is a challenging problem in structured light 3D shape measurement. Most of the existing methods achieve high dynamic range (HDR) measurement by sacrificing measurement speed, making them limited in high-speed ...
展开
Intensity saturation is a challenging problem in structured light 3D shape measurement. Most of the existing methods achieve high dynamic range (HDR) measurement by sacrificing measurement speed, making them limited in high-speed dynamic applications. This Letter proposes a generic efficient saturation-induced phase error correction method for HDR measurement without increasing any fringe patterns. We first theoretically analyze the saturated signal model and deduce the periodic characteristic of saturation-induced phase error. Based on this, we specially design a saturation-induced phase error correction method by joint Fourier analysis and Hilbert transform. Furthermore, the relationship among phase error, saturation degree, and number of phase-shifting steps is established by numerical simulation. Since the proposed method requires no extra captured images or complicated intensity calibration, it is extremely convenient in implementation and is applicable to performing high-speed 3D shape measurements. Simulations and experiments verify the feasibility of the proposed method. (C) 2022 Optica Publishing Group
收起
摘要 :
Multiple-wavelength optical fields on a detecting plane of an interferometer are generated from the interference signals detected for an object surface. The generated optical fields are backpropagated along the optical axis. An op...
展开
Multiple-wavelength optical fields on a detecting plane of an interferometer are generated from the interference signals detected for an object surface. The generated optical fields are backpropagated along the optical axis. An optical field along the optical axis is reconstructed by summing the backpropagated fields over the multiple wavelengths. The intensity and phase distributions of the reconstructed optical field provide the position of the object surface with an accuracy of a few nanometers. (c) 2007 Optical Society of America.
收起
原文获取