Dual-frequency grating method based research on phase measurement profilometry (PMP) technology

In the three-dimensional (3D) measurement, phase measuring profilometry (PMP) requires no less than three deformed sinusoidal patterns, limiting its applications to static scenarios only. In this paper, a stroboscopic online PMP for fast rotating object with binary dithered patterns is proposed. N frames of novel circular binary grating patterns are designed to measure a rotating object. A defocused digital light projector projects the designed patterns onto the object with stroboscopic method, the corresponding deformed patterns can be “frozen” by charge-coupled device (CCD) camera. Owing to the repeatability and periodicity of rotating movement, a synchronization control unit is used to keep the object at the fixed position in each “frozen” deformed pattern. Every projected pattern is shifted from the previous pattern by a factor of 2π/N. This method makes the images of the object appear stationary in the deformed patterns. The experimental results show the accurate 3D shape of fast rotating object can be reconstructed with the proposed method.

A high-performance image processing system (HIPS) has been developed to provide two- dimensional image acquisition for a variety of opti- cal applications. The system is built around two high-performance visible-light charged coupled device(CCD) arrays: a 32-port, 1024 x 1024 pixel array anda 16-port, 512 x 512 pixel array. The arrays and as- sociated circuitry were designed to operate at high frame rates, with an optical power dynamic range ofover 30 dB. The 512 x 512 array is designed to operateat over 800 frames per second; the larger device, atover 300 frames per second. The system has two main units: a stand-alone high-performance camera array module (HPCAM)and a VME-based image capture and display system(ICADS). HPCAM contains a CCD array and associ-ated drive and control electronics. ICADS consists ofan analog multiplexer, digitizer, digital frame buffer-integrator, main central processing unit (CPU) board with user and Ethernet interfaces, graphics driver, and high-resolution monitor.The CCD arrays used in this work are designed foruse in optical processing systems, such as radar ambi-guity, wide-band signal detection, and synthetic aper-ture radar (SAR) image formation processors. Thissystem provides a method for capturing and display-ing CCD array output data, giving the researcher amethod to analyze and develop CCD array and opti-cal processing systems.

Although there are various methods to measure the modulation transfer function (MTF) of charge-coupled devices (CCD), the interferometric fringe pattern method has advantages over others, such as canted slit sources, bar targets, knife-edge, laser-speckle patterns, random noise pattern, etc. Our interferometric method is relatively simple and versatile: It requires no critical optics and no focusing or precision alignment, the entry array is tested, the contrast ratio of the test pattern is high enough, the spatial frequency of the fringe pattern can vary continuously. Our method generates the formation of a sinusoidal intensity fringe pattern by the interference of two monochromatic plane waves, and straightforward projects it onto the CCD array under test. The construction of the experimental device is based on the Fresnel Double-Mirror structure. A 2.5 mw He-Ne laser with the wavelength of 632.8 nm is used as the light source, the laser beam is spatially filtered by a 10 μm pinhole and expanded to a diameter of 30 mm, and the resulting wave front is divided by two mirrors, which incline to each other at a small angle, and interfered. One of the mirrors is rotatable to vary the frequency of the pattern. The CCD array is mounted on a stage, which is also rotatable to make that the CCD array takes different angle with the fringe pattern direction, to receive the patterns. With the method we provided, the spatial frequency can be extended to some 2 times the Nyquist frequency of the CCD array to study the aliasing effect. In the Cartesian coordinates, the x- and y- axis MTFs (at angle 0° and 90°) of the CCD array were measured, the other three MTFs (at angle 26.56°, 45° and 63.44°), which nobody has done before, were also tested offering a more comprehensive characterization of the CCD array.

A new phase-unwrapping algorithm based on fringe frequency analysis is presented that will achieve greater automation and precision in measuring complex objects by phase-measuring profilometry (PMP). The new algorithm, which combines digital weighted filtering in the frequency domain and modulation ordering in the spatial domain, can recognize corrupt pixels automatically and produce a better phase-unwrapping path. By frequency weighted filtering, the analysis of fringe frequency is converted into the analysis of fringe modulation. Then, based on a strong correlation between local spatial frequency and the reliability of phase data, ordering of the filtered modulation produces an optimized unwrapping path. Simulation and experiments verify the new algorithm.

High precision phase measuring profilometry based on stereo microscope

In optical metrology, particularly in phase-measuring profilometry techniques, achieving both high measurement accuracy and high temporal resolution remains a long-standing challenge. For high-speed dynamic measurements, many existing methods still adopt a frame-by-frame processing strategy, tending to overlook the rich temporal information embedded across adjacent frames. This constraint makes it difficult to maintain robust performance under ultra-short exposure conditions. Taking fringe projection profilometry (FPP) as a representative example, we propose a physics-informed spatiotemporal fringe pattern analysis (PIST-FPA) framework that unifies physical modeling with deep learning for high-speed, high-fidelity three-dimensional (3D) reconstruction. Rather than processing each frame independently, PIST-FPA jointly analyzes a short sequence of fringe images within a temporal window, exploiting both spatiotemporal correlations and physics-based priors. PIST-FPA incorporates a background-estimation network for illumination correction, a physics-guided optical-flow alignment for motion compensation, and an attention-enhanced U-Net for spatiotemporal phase demodulation, forming a unified and interpretable learning-based processing pipeline. This hybrid paradigm effectively decouples object motion from surface morphology, enabling accurate and temporally consistent phase retrieval even under ultra-short exposure and low-signal-to-noise conditions. Both synthetic and real experiments at 10,000 frames per second demonstrate that PIST-FPA substantially outperforms both the conventional Fourier transform method and single-frame deep-learning method in terms of accuracy, robustness, and spatiotemporal consistency. By bridging physical modeling and data-driven learning in a unified spatiotemporal framework, PIST-FPA establishes a generalizable paradigm for physics-informed dynamic optical metrology, paving the way for next-generation high-speed phase-measuring profilometry and intelligent optical instrumentation.

A wireless refractive index sensor for in-line measurement in liquids was developed. It is based on the Fresnel reflection on a prism–liquid interface, where the critical angle of the totally reflected light in the interface of two media is detected by a charge-coupled device (CCD) array. A LED is used as a light source and a plastic optical fibre, with a well-established numeric aperture, guides the light to the prism interface. Both the LED and the CCD are controlled with a Raspberry Pi 3 Model B board with wireless communication. Resolutions with values lower than 1.0 × 10−4 RIU can be achieved with this potential low-cost configuration.

Recent advances in digital detector technology have paved the way to full-field digital mammography (FFDM) systems. The performance of these systems has evolved to the point where replacement of screen-film mammography (SFM) systems is becoming realistic. Despite some commonality between the two techniques, there are fundamental differences in how images are recorded, displayed, and stored. These differences necessitate an understanding of the principles of detection and the characteristics of digital images. Several approaches have been taken in the development of FFDM systems: (a) slot scanning with a scintillator and a charge-coupled device (CCD) array, (b) a flat-panel scintillator and an amorphous silicon diode array, (c) a flat-panel amorphous selenium array, (d) a tiled scintillator with fiberoptic tapers and a CCD array, and (e) photostimulable phosphor plates (computed radiography). Although the initial cost of an FFDM system is high compared with that of an SFM system, digital mammography has inherent advantages, such as wide dynamic range, reduction in recall rates, potential for reduction in radiation dose, increased patient throughput, postprocessing capability, and digital acquisition. These advantages and the rapidly occurring technologic developments will help establish FFDM as a mainstay of breast evaluation.

The difficulties related to InSAR DEM reconstruction and the computational burden necessary to get the final result strongly depend on the topography of the area of interest and accuracy requirements. Whenever high quality results are requested, a multi-interferograrn approach is strongly recommended, especially for repeat-pass interferometric data, such as ERS Tandem acquisitions. In this paper we recall the rationale of the multi-baseline strategy for DEM reconstruction and we propose a new phase unwrapping algorithm. In fact, phase unwrapping is the major obstacle to be overcome in the processing chain for InSAR DEM reconstruction, and often cannot be performed in a totally automatic way. Our attempt is to develop a robust processing chain that does not require user interaction and where possible prior information can be easily exploited. Preliminary results obtained by this algorithm are indeed very promising.

Light field imaging is an emerging technology in computational photography areas. Based on innovative designs of the imaging model and the optical path, light field cameras not only record the spatial intensity of threedimensional (3D) objects, but also capture the angular information of the physical world, which provides new ways to address various problems in computer vision, such as 3D reconstruction, saliency detection, and object recognition. In this paper, three key aspects of light field cameras, i.e., model, calibration, and reconstruction, are reviewed extensively. Furthermore, light field based applications on informatics, physics, medicine, and biology are exhibited. Finally, open issues in light field imaging and long-term application prospects in other natural sciences are discussed.

Phase unwrapping is a key step in InSAR (Synthetic Aperture Radar Interferometry) processing, and its result may directly affect the accuracy of DEM (Digital Elevation Model) and ground deformation. However, the decoherence phenomenon such as shadows and layover, in the area of severe land subsidence where the terrain is steep and the slope changes greatly, will cause error transmission in the differential wrapped phase information, leading to inaccurate unwrapping phase. In order to eliminate the effect of the noise and reduce the effect of less sampling which caused by topographical factors, a weighted least-squares method based on confidence level in frequency domain is used in this study. This method considered to express the terrain slope in the interferogram as the partial phase frequency in range and azimuth direction, then integrated them into the confidence level. The parameter was used as the constraints of the nonlinear least squares phase unwrapping algorithm, to smooth the un-requirements unwrapped phase gradient and improve the accuracy of phase unwrapping. Finally, comparing with interferometric data of the Beijing subsidence area obtained from TerraSAR verifies that the algorithm has higher accuracy and stability than the normal weighted least-square phase unwrapping algorithms, and could consider to terrain factors.

Calibration of wavelength is vital to the accurate assessment of Raman shifts using multichannel detectors, such as a charge-coupled device (CCD) detector in combination with multistage spectrometers. Although in zeroth order, the position in the image plane (i.e., CCD) may be approximated as linearly related to wavenumber, this approximation fails badly for accurate determinations of band position at even moderate spectral coverage (>50 cm−1). A Gaussian development of the imaging properties of a Czerny-Turner spectrometer leads to a quadratic relationship. However, the use of flat-field optics in modern triple monochromators results in position-wavenumber relationships that are not described well by a quadratic expression and are best fit by empirical relationships. Establishing the goodness of fit of several trial functions is the purpose of this current work. One way to achieve the relationship between position, or pixel number, and wavelength, as dispersed by a grating spectrometer, is to observe a standard sample that has several Raman lines of accurately known wavenumber shift. Indene, C9H8, has been used as such a standard for many years due to its well-calibrated and evenly spaced spectral features. This paper will explore the use of indene as a Raman shift calibration standard for CCD based spectrometers in the diagnostically important range of 700 to 1600 cm−1.

Depth estimation and camera calibration of a focused plenoptic camera for visual odometry

Recently, light field cameras have drawn much attraction for their innovative performance in photographic and scientific applications. However, narrow baselines and constrained spatial resolution of current light field cameras impose restrictions on their usability. Therefore, we design a hybrid imaging system containing a light field camera and a high-resolution digital single lens reflex camera, and these two kinds of cameras share the same optical path with a beam splitter so as to achieve the reconstruction of high-resolution light fields. The high-resolution 4D light fields are reconstructed with a phase-based perspective variation strategy. First, we apply complex steerable pyramid decomposition on the high-resolution image from the digital single lens reflex camera. Then, we perform phase-based perspective-shift processing with the disparity value, which is extracted from the upsampled light field depth map, to create high-resolution synthetic light field images. High-resolution digital refocused images and high-resolution depth maps can be generated in this way. Furthermore, controlling the magnitude of the perspective shift enables us to change the depth of field rendering in the digital refocused images. We show several experimental results to demonstrate the effectiveness of our approach.

With the development of semiconductor technology and the wide applications of data acquisition system, CCD (Charge Coupled Device) has made remarkable progress in image sensor and noncontact measurement field. The linear CCD data acquisition system based on MSP430F1611 micro controller is studied in this paper. The CCD output signal is captured by MSP430F1611 micro controller, and then the collected data are transmitted to the PC through a serial port and displayed on the interface compiled by VB. The system can be widely used in high accuracy and high speed measurement field.