In this paper, we present detail analysis and a step-by-step implementation of an optimized fringe projection profilometry (FPP) based 3D shape measurement system. First, we propose a multi-frequency and multi-phase shifting sinusoidal fringe pattern reconstruction approach to increase accuracy and sensitivity of the system. Second, phase error compensation caused by the nonlinear transfer function of the projector and camera is performed through polynomial approximation. Third, phase unwrapping is performed using spatial and temporal techniques and the tradeoff between processing speed and high accuracy is discussed in details. Fourth, generalized camera and system calibration are developed for phase to real world coordinate transformation. The calibration coefficients are estimated accurately using a reference plane and several gauge blocks with precisely known heights and by employing a nonlinear least square fitting method. Fifth, a texture will be attached to the height profile by registering a 2D real photo to the 3D height map. The last step is to perform 3D image fusion and registration using an iterative closest point (ICP) algorithm for a full field of view reconstruction. The system is experimentally constructed using compact, portable, and low cost off-the-shelf components. A MATLAB® based GUI is developed to control and synchronize the whole system.

As high-quality 3D range scanners become increasingly adopted, a common issue emerges that is how best to properly store captured 3D data as it inherently contains a large amount of information per each frame. One approach that has proved successful is to convert 3D range data to 2D regular color images that can be further compressed using traditional image compression techniques (e.g., JPEG). In literature, there are three major conversion methods: (1) virtual fringe projection; (2) direct depth encoding; and (3) multiwavelength depth en- coding. This paper compares the effectiveness and limitations of all three major compression methods, especially when the resultant 2D images are stored with low-quality lossy (i.e., JPEG) image formats. Experimental data found that multiwavelength depth encoding outperforms both other methods, especially under various levels of lossy JPEG compression. Principles of each method will be explained, and experimental data will be presented to evaluate each method.

In this paper, the Transport of Intensity Equation (TIE) for testing of an aspheric surface is verified experimentally. Using simulation, a proper defocus distance Δ𝑧 that leads to an accurate solution of TIE is estimated whenever the conic constant and configuration of the experiment are known. To verify this procedure a non-nulled experiment for testing an aspheric is used. For verification of the solution, the results are compared with the Shack-Hartmann sensor. The theoretical method and experimental results are compared to validate the results.

Within the field of quality control and dimensional metrology, the evolutions in the domain of production processes are triggering more use of non-contact measurement equipment to assure faster feature assessment where possible. This led to the development of for instance laser line scanners. The standardization of these new tools follows these novel evolutions. As the coordinate measuring systems (CMSs) which include coordinate measuring machines (CMMs) with its diversity in measurement probes widens its spectrum, the ISO 10360 standard series is rearranged and split up in more parts, covering specific probe groups. The previously mentioned laser line scanners, that can be equipped on a CMM, are integrated within ISO 10360-8 which applies for CMMs equipped with optical distance sensors. This paper is an example of how to interpret and apply this standard to a specific optical distance sensor. This has to be done by taking into account the sensor’s characteristics. The intrinsic properties in the technique require an in-depth look at the recommended guidelines within the standard. Furthermore, the guidelines are adapted to use the same capabilities of the laser line scanner, which are used for measuring, without eliminating the uncertainties present in practical use of the sensor. The verification tests and their implementation are discussed, adapted to the sensors needs and performed on a state-of-the-art CMM. The verification parameter results are determined, presented and critically evaluated.

Structured light methods are used by many commercial products on the market today. Many such systems using white light projectors while many line gages use standard red laser diodes. However, in recent years there has been much claimed about using blue light, polarized light and partially coherent systems to obtain better performance. Unlike interferometers, moving from red to blue light for a system using only geometric shape information does not gain an automatic advantage from the shorter wavelength. The sensitivity metric does not have a wavelength component to it. But there are other factors that can improve gage performance. The ability to measure some feature is also a function of other parameters such as signal to noise ratio, reflectivity variations, and depth-of-field over which a clear pattern can be seen. This paper will explore the theoretical and experimental data relating to what works and what can be expected from variations on the old methods.

Large spacecraft missions have both technical and financial needs. Technical needs drive the inclusion of numerous subsystems, which must be configured or deployed. Financial needs, for many spacecraft, are filled through generating public support, which is enhanced by being able to show the spacecraft in operation. This paper presents DeSCJOB, a small satellite that is deployed from a larger spacecraft. It launches from the parent spacecraft, captures images of whatever is desired (moving around the larger spacecraft, if desired) and then retracts back to its docking point automatically. Its utility for operational and public relations imaging is discussed.

Urban ecosystem studies require monitoring, controlling and planning to analyze building density, urban density, urban planning, atmospheric modeling and land use. In urban planning, there are many methods for building height estimation using optical remote sensing images. These methods however, highly depend on sun illumination and cloud-free weather. In contrast, high resolution synthetic aperture radar provides images independent from daytime and weather conditions, although, these images rely on special hardware and expensive acquisition. Most of the biggest cities around the world have been photographed by Google street view under different conditions. Thus, thousands of images from the principal streets of a city can be accessed online. The availability of this and similar rich city imagery such as StreetSide from Microsoft, represents huge opportunities in computer vision because these images can be used as input in many applications such as 3D modeling, segmentation, recognition and stereo correspondence. This paper proposes a novel algorithm to estimate building heights using public Google Street-View imagery. The objective of this work is to obtain thousands of geo-referenced images from Google Street-View using a representational state transfer system, and estimate their average height using single view metrology. Furthermore, the resulting measurements and image metadata are used to derive a layer of heights in a Google map available online. The experimental results show that the proposed algorithm can estimate an accurate average building height map of thousands of images using Google Street-View Imagery of any city.

Visual Inspection is the most common means for inspecting manufactured parts for random defects such as pits, scratches, breaks, corrosion or general wear. The reason for the need for visual inspection is the very random nature of what might be a defect. Some defects may be very rare, being seen once or twice a year, but May still be critical to part performance. Because of this random and rare nature, even the most sophisticated image analysis programs have not been able to recognize all possible defects. Key to any future automation of inspection is obtaining good sample images of what might be a defect. However, most visual check take no images and consequently generate no digital data or historical record beyond a simple count. Any additional tool to captures such images must be able to do so without taking addition time. This paper outlines the design of a potential visual inspection station that would be compatible with current visual inspection methods, but afford the means for reliable digital imaging and in many cases augmented capabilities to assist the inspection. Considerations in this study included: resolution, depth of field, feature highlighting, and ease of digital capture, annotations and inspection augmentation for repeatable registration as well as operator assistance and training.

Fringe projection is a well-established optical method for the non-destructive contactless three-dimensional (3D) measurement of object surfaces. Typically, fringe sequences in the visible wavelength range (VIS) are projected onto the surfaces of objects to be measured and are observed by two cameras in a stereo vision setup. The reconstruction is done by finding corresponding pixels in both cameras followed by triangulation. Problems can occur if the properties of some materials disturb the measurements. If the objects are transparent, translucent, reflective, or strongly absorbing in the VIS range, the projected patterns cannot be recorded properly. To overcome these challenges, we present a new alternative approach in the infrared (IR) region of the electromagnetic spectrum. For this purpose, two long-wavelength infrared (LWIR) cameras (7.5 - 13 μm) are used to detect the emitted heat radiation from surfaces which is induced by a pattern projection unit driven by a CO₂ laser (10.6 μm). Thus, materials like glass or black objects, e.g. carbon fiber materials, can be measured non-destructively without the need of any additional paintings. We will demonstrate the basic principles of this heat pattern approach and show two types of 3D systems based on a freeform mirror and a GOBO wheel (GOes Before Optics) projector unit.

Visual inspection of parts or structures for defects typically requires good spatial resolution to see the defects, but may also require a large focus range. But to obtain the best resolution from an imaging system, it needs to have a low f-number which limits the usable depth of field. Methods to use autofocus or focus stacking provides more range at high resolution, but often at the expense of computation time, loss of a real time image and uncertainty in scale changes. This paper describes an approach to quickly move through a range of focus positions without the need to move optics mechanically in a manner that is highly repeatable, maintains high resolution and provides the potential for a live image directly viewable by an inspector, even at microscope level magnifications. This paper will present the approach we investigated and discuss the pros and cons for a range of applications from large structures to small feature inspection. The paper will present examples of what resolution was achieved and how the multiple images might also be used to determine other parameters such as pose of a test surface.

This paper proposes a method that does not require to change exposure time of the camera for high-quality surface measurement when the surface contrast is large. The idea is that three phase-shifted inverted fringe patterns are used to complement regular three phase-shifted fringe patterns for phase retrieval. For saturated pixels, the inverted fringe patterns will be used in lieu of the original patterns for phase computation. Though not as robust as some of previously proposed time-consuming methods, experimental data showed that the proposed method can substantially increase measurement quality for high-contrast surfaces.

Pattern projection-based three-dimensional (3-D) measurement systems are well established in various application fields. However, for some time, there has been an increasing demand in terms of a higher measurement speed in order to analyze fast processes. We introduce a GOBO slide-based projector (GOes Before Optics) providing high speed, high radiant flux, and eye-safe incoherent light at low cost. We present its setup as well as the generation and change of the projected patterns. We explain the 3-D measurement principle and show first measurements of an inflating airbag and a rope skipper conducted at a 3-D frame rate of more than 1.3 kHz.

X-ray computed tomography (CT) is slowly conquering its space in the manufacturing industry for dimensional metrology and quality control purposes. The main advantage is its non-invasive and non-destructive character. Currently, CT is the only measurement technique that allows full 3D visualization of both inner and outer features of an object through a contactless probing system. Using hundreds of radiographs, acquired while rotating the object, a 3D representation is generated and dimensions can be verified. In this research, this non-contact technique was used for the inspection of assembled components. A dental cast model with 8 implants, connected by a screwed retained bar made of titanium. The retained bar includes a mating interface connection that should ensure a perfect fitting without residual stresses when the connection is fixed with screws. CT was used to inspect the mating interfaces between these two components. Gaps at the connections can lead to bacterial growth and potential inconvenience for the patient who would have to face a new surgery to replace his/hers prosthesis. With the aid of CT, flaws in the design or manufacturing process that could lead to gaps at the connections could be assessed.

Interferometric based techniques are often used for 3D quantitative phase imaging. While these techniques are sensitive to vibrations, non-interferometric intensity based techniques such as the transport of intensity equation (TIE) do not suffer from such a drawback. Phase reconstruction of phase objects using TIE technique is accomplished by recording several diffraction patterns at different observation planes through axially translating the CCD. In this paper, we purpose to use a spatial light modulator (SLM) in a modified 4f TIE optical setup to acquire 3D tomographic images of phase objects. This modified setup will reduce the acquisition time dramatically making the TIE technique useful for dynamic events such as biological samples. We illustrate how 3D phase objects can be reconstructed tomographically by constructing a rotating mechanism for the sample. At each angle of rotation, two diffraction patterns are captured by the CCD either sequentially or instantaneously with the help of a reference mirror. The reconstructed optical fields are tomographically recomposed to yield the final 3D shape using a tomographic backprojection technique. Finally, a reconfigurable hardware controlled by a GUI is employed to synchronize the CCD, the SLM and the rotating stage.

High contrast imaging, in the presence of a bright background, is a challenging problem encountered in diverse applications ranging from the daily chore of driving into a sun-drenched scene to in vivo use of biomedical imaging in various types of keyhole surgeries. Imaging in the presence of bright sources saturates the vision system, resulting in loss of scene fidelity, corresponding to low image contrast and reduced resolution. The problem is exacerbated in retro-reflective imaging systems where the light sources illuminating the object are unavoidably strong, typically masking the object features. This manuscript presents a novel theoretical framework, based on nonlinear analysis and adaptive focal plane transmittance, to selectively remove object domain sources of background light from the image plane, resulting in local and global increases in image contrast. The background signal can either be of a global specular nature, giving rise to parallel illumination from the entire object surface or can be represented by a mosaic of randomly orientated, small specular surfaces. The latter is more representative of real world practical imaging systems. Thus, the background signal comprises of groups of oblique rays corresponding to distributions of the mosaic surfaces. Through the imaging system, light from group of like surfaces, converges to a localized spot in the focal plane of the lens and then diverges to cast a localized bright spot in the image plane. Thus, transmittance of a spatial light modulator, positioned in the focal plane, can be adaptively controlled to block a particular source of background light. Consequently, the image plane intensity is entirely due to the object features. Experimental image data is presented to verify the efficacy of the methodology.

Fiber faceplate modulation was applied to read out the precise actuation of silicon-based, surface micro-fabricated cantilever mirrors array in optical imaging system. The faceplate was made by ordered bundles consisting of as many as ten thousands fibers. The transmission loss of an individual fiber in the bundles was 0.35dB/cm and the cross talk between neighboring fibers in the faceplate was about 15%. Micro-cantilever mirrors array (Focal-Plane Array (FPA)) which composed of two-level bi-material pixels, absorb incident infrared flux and result in a temperature increase. The temperature distribution of incident flux transformed to the deformation distribution in FPA which has a very big difference in coefficients of thermal expansion. FPA plays the roles of target sensing and has the characteristics of high detection sensitivity. Instead of general filter such as knife edge or pinhole, fiber faceplate modulate the beam reflected by the units of FPA. An optical readout signal brings a visible spectrum into pattern recognition system, yielding a visible image on monitor. Thermal images at room temperature have been obtained. The proposed method permits optical axis compact and image noise suppression.