TDI imaging and scanning moiré for online defect detection

This paper explains the application of scanning moiré in association with TDI (Time Delay and Integration) imaging for complete peripheral inspection of cylindrical objects. Based on the structured light technique, a grating pattern modulated by deformations, such as dents on the surface of a rotating cylindrical object, is recorded using a TDI camera. The illumination system consists of an intensity modulated, line generating laser diode aligned at an angle to the camera axis. By using the TDI option for recording every nth line, an online scanning moiré pattern is generated. After providing a simple explanation of the scanning moiré, the effects of object rotation speed and TDI scan speed on the fringe pattern are discussed and demonstrated. The techniques presented here offer low cost solutions to industrial machine vision tasks related to peripheral imaging and inspection of cylindrical objects.     

Improved spatial phase detection for profilometry using a TDI imager

Performance of a time delay and integration (TDI) imager is analogous to a drum/periphery camera. Coupled to a modulated line generating laser diode, it is possible to use a TDI imager to encode the shape profile of a rotating cylindrical object as deformed gratings in a digital image. Among the various methods for extracting the phase from a deformed grating, the spatial phase detection (SPD) method is fast and easy to use. Errors are introduced in this method if the phase gradient is high over a grating interval. Here we propose a method to reduce the phase gradient by using a TDI feature which makes it possible to record images at variable lateral magnification.     

三维面形测量技术的新进展

三维面形测量是获取物质形态特征的一种重要手段，也是记录，比较，复制物体形态特征 的基础，三维面形测量技术在机器视觉，自动加工，工业检测，产品质量控制，实物仿形，生物和医学等领域具有重要意义和广阔的应用前景。     

Microlens array recording of localized retinal responses

We designed a rapid functional imager for the parallel recording of localized intrinsic optical signals (IOSs). This imager used a microlens array (MLA)-based illuminator to deliver visible stimulus light and near-infrared (NIR) recording light simultaneously. The parfocal configuration of the stimulus and recording light illumination enabled confocal recording of the stimulus-evoked IOSs. Because the MLA stimulation/recording spots were widely separated on the retina, and only the photoreceptors within the MLA stimulation/recording spots were stimulated, the potential IOS cross talk effect among neighboring retinal areas was minimized. Our experiments revealed robust IOS activities tightly correlated with localized retinal responses.     

Polarization imaging for 3D inspection of highly reflective metallic objects

In the field of industrial vision, the 3D inspection of highly reflective metallic objects is still a delicate task. The specular reflections prevent the use of a 3D laser scanner, whereas the phase shifting-based 3D systems are more adapted to inspect surfaces with low curvature. This paper deals with a new automated 3D inspection system based on polarization analysis. Studying the state of polarization of the reflected light is very useful for obtaining information on the normals of the surface. An extension of the shape from polarization method from dielectric to metallic surfaces is demonstrated. Then, an improved relaxation algorithm is provided in order to reconstruct the shape from the normal field given by the polarization analysis. Finally, applications to shape defect detection are discussed and the efficiency of the system in discriminating defects on highly reflective metallic objects made by stamping and polishing is presented. The text was submitted by the authors in English.     

The ‘fringe method’ and its application to the measurement of deformations,vibrations, contour lines and differences of objects

A variable sensitivity technique using the projection of a fringe pattern is demonstrated for mapping deformations, vibrations, contour lines and differences between two objects. The method does not require laser illumination and gives an opportunity for studying large objects with incoherent light, and is compared with other techniques such as holography or speckle. The limitations likely to be encountered in industrial environments are discussed. The realization and incoherent projection of gratings is also discussed.     

Noise analysis and measurement of time delay and integration charge coupled device

Time delay and integration (TDI) charge coupled device (CCD) noise sets a fundamental limit on image sensor performance,especially under low illumination in remote sensing applications.After introducing the complete sources of CCD noise,we study the effects of TDI operation mode on noise,and the relationship between different types of noise and number of the TDI stage.Then we propose a new technique to identify and measure sources of TDI CCD noise employing mathematical statistics theory,where theoretical analysis shows that noise estimated formulation converges well.Finally,we establish a testing platform to carry out experiments,and a standard TDI CCD is calibrated by using the proposed method.The experimental results show that the noise analysis and measurement methods presented in this paper are useful for modeling TDI CCDs.     

Three Dimensionality of the Recognized Visual Space of Illumination Proved by Hidden Illumination

We hypothesized that the recognized visual space of illumination (RVSI) was constructed in our brain when we grasped the state of illumination of a space. The importance about the RVSI is that it is three dimensional and is valid not only at the surfaces of the existing objects in the space, but also for the entire portion in the space where no objects exist. With this property of RVSI we are able to predict the appearance of an object surface in terms of lightness as well as of color when the object shifts from one place to the other in the space. The three dimensionality of the RVSI is proved by giving a hidden illumination within a space and by asking a subject to judge the lightness or color of a test patch placed in the area of the hidden illumination. In spite of the additional light on the test patch the subject did not recognize that the light was added but simply felt that the surface was made of a higher lightness or colored by transferring the light into an increase of the reflectance factor of the test patch. The results can be interpreted if we assume that a same RVSI exists throughout the entire space including the area of the hidden illumination.     

Non-contact measurement of angle of view between the inspected surface and the thermal imager

The angle of view between inspected object and thermal imager influences the values of temperature measured by infrared thermography. This happens because the emissivity depends on the angle of radiation, and because the apparent temperature measured is influenced by that angle of view combined to thermal imager’s field of view. Therefore, it is necessary to know the angle of view during thermographic inspection, which is generally not feasible due to safety reasons. This paper develops a method of measuring the angle of view with no contact with the inspected object, by employing laser distance meters, commonly available in the market.     

Longitudinal-differential interferometry: direct imaging of axial superluminal phase propagation

We introduce and demonstrate a new interferometric method called longitudinal-differential (LD) interferometry, which measures the spatially resolved phase difference of the scattered field by an object relative to the illumination. This method is combined with a high-resolution interference microscope that allows recording three-dimensional field distributions in amplitude and phase. The method is applied to study the axial phase behavior of Arago spots, an effect observable in low-Fresnel-number systems behind objects with a size comparable to the wavelength. We directly observe the initial phase delay in the Arago spot and prove that the local phase velocity exceeds the speed of light in air. Such LD phase studies are applicable not only to the Arago spot but also to other kinds of light interactions with wavelength-scale objects, e.g., photonic nanojets.     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H₁.然后将H₁作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H1.然后将H1作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

Optical three-dimensional sensing by phase measuring profilometry

The technique of phase-measuring profilometry is reviewed, whereby a sinusoidal grating structure is projected onto a diffuse three-dimensional surface, and the resulting deformed grating image is detected by a solid state array camera and processed by a microcomputer using interferometric phase measuring algorithms. The approach permits parallel acquisition and processing of large amounts of data with high accuracy and speed.Several systems are described, configured with telecentric laser light illumination or general white light diverging illumination, and capable of measurement from a single point of view or over full 360°. Each system consists of an optical projection assembly with phase-shifter, an imaging assembly with high density CCD camera and an IBM AT microcomputer with buffer and control cards.Applications to industrial inspection and medical diagnostics are presented.     

Effect of metals on UV-excited plasmonic lithography for sub-50 nm periodic feature fabrication

This paper describes and compares the effect of metal films, such as aluminum (Al) and silver (Ag) on UV-excited two-beam surface plasmon interference nanolithography. A planar four-layer configuration has been employed to study the light intensity distribution on the recording medium. It is observed that high-density sub-50 nm periodic structures were achievable by employing the above-mentioned metal films when interrogated with p-polarized, 364 nm illumination wavelength source. It is found that the obtained periodic feature shows good exposure depth and high contrast when Al is used as a metal film. The initial experimental result of planar four-layer configuration is also presented.     

Laser speckle reduction using motionless image conduits

We have demonstrated a speckle reduction method using motionless image conduits (MICs). Different experimental conditions by introducing the high-coherence HeNe laser and the low-coherence laser diode (LD) as the illumination light sources, by employing the straight MIC and the curved MIC as the speckle reduction components, and by recording speckle images without (objective speckle) and with (subjective speckle) the imaging lens mounted on the CCD camera are conducted, respectively. The most efficient speckle reduction condition is found by the combination of using the LD and the curved MIC, where the objective speckle contrast ratio is reduced from 0.7378 to 0.1725. Experimental results are discussed, and the causes for these speckle reduction efficiency changes are given.     

预放大数字全息显微系统的特点

为了提高预放大数字全息显微系统的成像质量,采用理论分析与实验验证相结合的方法,分别对采用平面及球面参考光记录的预放大数字全息显微系统进行了研究和比较。结果表明:在通常的实验条件下,系统的横向分辨力主要取决于显微物镜的成像分辨力;记录距离较小时,两种系统的横向分辨力均随着记录距离的增大略有降低;但当记录距离较大时,球面参考光预放大数字全息系统的横向分辨力降低得更为明显,即平面参考光预放大数字全息显微系统较为优越;在记录距离为0的情况下,即像面数字全息成像情况下,两种系统的再现像均具有最高的分辨力,在利用普通工业用传感器条件下,横向分辨力远超过了2.19 m,且像质较好。因此,尽可能减小全息图的记录距离,或者采用像面数字全息系统,可以有效提高数字全息系统的成像分辨力。     

Rapid 3D surface profile measurement of industrial parts using two-level structured light patterns

This paper aims to present a rapid 3D shape measurement system based on novel monochromatic structured light patterns. The system consists of projectors shooting the fringe patterns onto the inspected parts and cameras recording the corresponding distorted images. Using the two-level fringe patterns, the correspondence between the projector image and camera image can be established with sub-pixel accuracy. The two-level pattern is based on three spatiotemporal binary stripes, in which the value of the stripe boundary (first-level coding) is determined by the two adjacent stripes patterns over time and the codeword of the strip boundary (second-level coding) depends on its values and neighbor boundary values in space. The proposed pattern is robust to ambience light variation and part texture. Moreover, the occlusion can be overcome and high density measurement can be achieved. Experiments with different 3D parts are conducted to evaluate the robustness and accuracy of the inspection system using the two-level patterns. The results show that the system has desired properties of high accuracy, high density, rapid acquisition, and robustness, which are essential for industrial application.     

High-speed three-dimensional shape measurements of objects with laser speckles and acousto-optical deflection

Many three-dimensional (3D) shape measurement techniques in stereophotogrammetry with temporal coded structured illumination are limited to static scenes because the time for measurement is too long in comparison to the object speed. The measurement of moving objects result in erroneous reconstructions. This is apparent to reduce measurement time to overcome this limitation, which is often done by increasing the projection rate for illumination while shrinking the amount of images taken for reconstruction. The projection rate limits most applications in its speed because digital light processing (DLP) projectors, which are widely used, bring a limited projection rate along. Our approach, in contrast, does not take a DLP. Instead we use laser speckles as projected patterns which are switched using an acousto-optical deflector. The projection rate is 10× higher than what the fastest stripe projection systems to our knowledge achieve. Hence, we present this uncommon but potential approach for highspeed (≈250 3Dfps= [3D measurements per second]), dense, and accurate 3D measurements of spatially separated objects and show the media that emphasizes the ability of accurate measurements while the objects under testing move.     

Essay Review-Scholarly froth and engineering skeletons

Holography is a two-stage process of photography using coherent light from a laser to illuminate the scene. In the first stage a hologram is formed by combining the light scattered from the object and the direct laser beam on a photographic plate. In the second stage a three-dimensional image is reconstructed without the use of lenses, by directing the laser beam through the hologram. Applications of holography include information storage, recording of images in depth, the use of holograms as optical elements, and as a means of performing precise interferometric measurements on three-dimensional objects of any shape and surface finish.     

Real-time reflection imaging with terahertz camera and quantum-cascade laser

A real-time reflection imaging employing a terahertz （THz） camera as the imager and a 3.9 THz quantum- cascade laser （QCL） as the light source is demonstrated. The imaging light is collected and guided by only one off-axis parabolic mirror. The imaging distance is about 1 m. THz images of a coin and a knife are aacquired and analyzed. An actual soatial resolution with a value of about 0.33 mm is achieved.