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Remote sensing finds more and more applications, from industrial control, to face recognition, not forgetting terrain surveying. This trend is well exemplified by fringe projection techniques, which enjoyed a considerable development in the recent years. In addition of high requirement in terms of measurement accuracy and spatial resolution, the en...
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... However, in actual measurement, the background intensity and the fringe amplitude are not always stable due to the fluctuations of the projection light source [11][12][13], which is usually caused by instable driving power and aging projector bulbs [14]. Ref. [15] found that the instability of the projected light intensity and producing considerable random changes. Ref. [16] verified that the fluctuations causes the intensities vary randomly with time, which may vary slowly in a long period of capture time while may also vary sharply in a short period of capture time. ...
Fringe projection profilometry (FPP) usually uses a projector with an instable light source due to the unsatisfactory driving power. As a result of the fluctuations of the projection light source, the fringe captured by a camera deviates from its ideal distribution, from which, the calculated phase has a random phase error, thus reducing the 3-D measurement accuracy. We found that the random phase error influences both the system calibration and the 3-D reconstruction, where the influence on the system calibration has not been previously noticed. In this paper, we formulate the phase error model of the phase-shifting algorithm caused by the fluctuations of the projection light source, and analyze its interference on calibration and reconstruction, respectively. From which, an accurate FPP using a combination of accurate calibration and accurate 3-D reconstruction is proposed, which are performed by using a deep learning-based phase calculation method. The provided experimental results verify that the proposed FPP can obviously improve the measurement accuracy.
... In addition to gains in optical efficiency, this design minimizes colour moiré and may, in principle, also allow higher spatial resolution. 11,12 The latter possibility, however, is limited in the case of silicon due to its indirect band gap, requiring thick absorptive layers. In addition, this configuration requires a more complex and costly manufacturing process. ...
Herein we demonstrate that solution-grown single crystals of semiconducting methylammonium lead halide perovskites (MAPbX3, where MA=CH3NH3+, X=Cl−, Br− and Br/I−) can be used as semiconductor absorbers for full-colour imaging. A one-pixel photodetector prototype was constructed by stacking three layers of blue-, green- and red-sensitive MAPbCl3, MAPbBr3 and MAPb(Br/I)3 crystals, respectively. The prototype detector was demonstrated to recognize and faithfully reproduce coloured images by recombination of the signals from each individual colour channel. This layered structure concept, besides imparting a two- to three-fold reduction in the number of required pixels, also offers several other advantages over conventional technologies: three times more efficient light utilization (and thus higher sensitivity) than common Bayer scheme devices based on dissipative optical filters, colour moiré suppression and no need for de-mosaic image processing. In addition, the direct band gap structure of perovskites results in optical absorption that is several orders of magnitude greater than silicon. This opens a promising avenue towards the reduction of pixel-size in next-generation devices as compared with conventional silicon-based technologies.
... This approach makes the fringe acquisition as simple as in single-wavelength case. Following three different approaches have been used for 3-colour recording: (a) Bayer filter 1-CCD sensor [52][53][54][55], (b) 3-CCD sensor [24,49,52,56], and (c) Foveon X3 sensor [46,52,57]. We will discuss these three strategies for simultaneous recording of 3-colours in Section 4. ...
... The Foveon X3 sensor based camera has been used in whitelight interferometric applications [67], aerodynamic flow analysis using digital three-colour holographic interferometry [46,52], surface profiling using snap-shot fringe projection profilometry [57]. The RGB interferometry that uses a RGB CCD camera to acquire multiple wavelength interferograms simultaneously is a simpler, faster, and dynamic tool for metrology and imaging applications. ...
Interferometry has been widely used for optical metrology and imaging applications because of their
precision, reliability, and versatility. Although single-wavelength interferometery can provide high sen-
sitivity and resolution, it has several drawbacks, namely, it fails to quantify large-discontinuities, large-
deformations, and shape of unpolished surfaces. Multiple-wavelength techniques have been successfully
used to overcome the drawbacks associated with single wavelength analysis. The use of colour CCD
camera allows simultaneous acquisition of multiple interferograms. The advances in colour CCD cameras
and image processing techniques have made the multi-colour interferometry a faster, simpler, and cost-
effective tool for industrial applications. This article reviews the recent advances in multi-colour inter-
ferometric techniques and their demanding applications for characterization of micro-systems, non-
destructive testing, and bio-imaging applications.
... • The third design uses 3 stacked photosensitive layers, each of which has its own spectral sensitivity and is transparent for other colors. This design deals in an elegant way with the positioning problems of the 3-chip solution above (Equis et al., 2011). • A fourth design, which is generally implemented in scientific cameras, uses color filter modules combined with a single sensor. ...
... With these cameras, real-time color or monochromatic images can be produced at lower resolution for exploring and focusing purposes. A new development is the layered CCD sensor (Equis et al., 2011), where layers of photo elements sensitive for red, green or blue light, respectively, are stacked, on top of each other. Therefore, one photo element is actually composed of 3 distinct photo elements compacted by a grid that distributes the light equally over each photo element. ...
Microscopy-based imaging is booming and the need for tools to retrieve quantitative data from images is urgent. This book provides simple but reliable tools to generate valid quantitative gene expression data, at the mRNA, protein and activity level, from microscopic images in relation to structures in cells, tissues and organs in 2D and 3D. Volumes, areas, lengths and numbers of cells and tissues can be calculated and related to these gene expression data while preserving the 2D and 3D morphology. Image cytometry thus provides a comprehensive toolkit to study molecular processes and structural changes at the level of cells and tissues.
Phase-shifting is a powerful phase demodulation method for three-dimensional imaging by fringe projection. However, numerous fringe patterns, which encode a single-phase function, are required. In this paper, the use of intensity patterns, which encode multiple phase functions, is proposed. A multi-demodulation phase-shifting algorithm and the intensity pattern projection profilometry approach are developed. A computer simulation and an experimental three-dimensional object measurement are performed to validate the proposal and demonstrate its effectiveness. The results exhibit that a similar accuracy than conventional fringe projection is achieved while using a reduced number of patterns. The proposed approach is a feasible alternative to increase the efficiency of three-dimensional imaging systems based on phase-shifting.
With phase-shifting technique, the illumination fluctuations may decrease measurement accuracy. This paper presents a simple method for solving this problem by use of fringe histograms. A fringe pattern containing bright and dark fringes is recognized as an image having two classes of pixels following a bimodal histogram, and the optimal threshold for segmenting this pattern enables maximizing its intervariance between the two classes. Using this optimal threshold, some statistics of the segmented classes, that is, their means, keep stable during phase shifting. Using these means of classes as nodes allows us to determine a linear transformation function by which the fluctuations of the fringe patterns in background intensities and modulations are corrected. Numerical simulation and experimental results demonstrate this method to be efficient and effective in improving the phase measuring accuracies with phase-shifting technique. (C) 2015 Optical Society of America
Abstract. In this study, an optical system capable of simultaneously grabbing three phase-shifted interferometric images was developed for dynamic temperature field measurements of a thin flame. The polarization phase-shifting technique and a Michelson interferometer that is coupled to a 4-f system with a Ronchi grating placed at the frequency plane are used. This configuration permits the phase-shifted interferograms to be grabbed simultaneously by one CCD. The temperature field measurement is based on measuring the refraction index difference by solving the inverse Abel transform, which requires information obtained by the fringe order localization. The phase map is retrieved by a three-step algorithm. Experimental results of a dynamic thin flame are presented.
