Conference Paper: Improved measurement dynamic range for point triangulation probes[Show abstract] [Hide abstract] ABSTRACT: Point triangulation probes have been in use in industry for half a century. In that time, there has not been any big changes in the mechanism by which they operate A point laser triangulation gage bought today has about the same ratio of standard deviation to measurement range, or measurement dynamic range, as one bought 30+ years ago. A significant limiting factor of the measurement dynamic range of such sensors is the noise seen by the sensor, which consists of both classic speckle noise, but also the effects of surface texture on the reflected beam. This paper will discuss four different methods, based upon advances applied in other optical metrology systems that improve the standard deviation to measurement range ratio for point laser triangulation gages by a factor of 20 on average. We will present the theory of how each of these methods provide this improved measurement dynamic range as well as the results of laboratory tests made on breadboard systems.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, we present an occlusion removal method to enhance reconstructed images of occluded three-dimensional (3D) objects based on pixel depth mapping technique in 3D multi-perspective imaging. Depth mapping is achieved by minimizing the statistical variance of projection image pixels of 3D object points on different perspective images. Then depth map and variance map are utilized to classify elemental image pixels into object or occlusion classes. Based on pixel classification results, a modified reconstruction algorithm is used to reconstruct the object without the effect of occlusion. In the proposed method, the occlusion is unknown and may be arbitrarily placed in front of the scene. Experimental results are presented to evaluate the effectiveness of the proposed method.
- [Show abstract] [Hide abstract] ABSTRACT: The performance of multiview three-dimensional imaging systems depends on several factors, including the number of sensors, sensor pixel size, relative sensor configuration, imaging optics, and computational reconstruction algorithm. Therefore, it is important to compare the performance of such systems under equally constrained resources. In this Letter, we develop a unifying framework to evaluate the lateral and axial resolution of N-ocular imaging systems ranging from stereo (two cameras) to multiple sensors (integral imaging) under fixed resource constraints. The proposed framework enables one to evaluate the system performance as a function of sensing parameters such as the number of cameras, the number of pixels, parallax, pixel size, lens aperture, and focal length. We carry out Monte Carlo simulations based on this framework to evaluate system performance as a function of sensing parameters. To the best of our knowledge, this is the first report on quantitative analysis of N-ocular imaging systems under common resource constraints.
Conference Paper: Surface sensitivity reduction in laser triangulation sensors[Show abstract] [Hide abstract] ABSTRACT: Laser triangulation sensors offer a simple, non-contact and fast solution to measure displacement, position, vibration and thickness. However, these sensors are prone to target surface sensitivity since they rely heavily on a uniform back-scatter of the laser spot. Here, sources of measurement noise including surface texture, speckle, beam deflection and asymmetry are discussed. In addition, a few solutions using dithering as well as the beam shaping to reduce surface sensitivity are explored. It is shown that a simple ditherer would induce additional error and a solution is suggested to compensate for it.
- [Show abstract] [Hide abstract] ABSTRACT: Techniques in 3-D digital holographic microscopy (DHM) integrated with numerical processing are enabling researchers to obtain rich, quantitative information about the structure of cells and microorganisms in noninvasive real-time conditions. In single-exposure DHM, a digital Fresnel hologram is recorded from the specimen in either on-axis or off-axis configurations. The microscope objective that is used for magnifying the field can be removed in a lensless implementation. One can reconstruct the specimen's 3-D image, or a stack of 2-D images, from the recorded digital hologram by inverse Fresnel transformation. Cross-comparison with 2-D intensity images has shown that complex 3-D images that are reconstructed from digital holograms provide more discriminating features and allow for better classification of cells. The 3-D reconstruction of cells can be used with statistical pattern recognition algorithms to recognize and classify the cells in real-time.
- [Show abstract] [Hide abstract] ABSTRACT: Integral imaging is a 3D sensing and imaging technique. Conventional 3D integral imaging systems require that all the sensor positions in the image capture stage are known. But in certain image pick up geometries, it may be difficult to obtain accurate measurement of sensor positions such as sensors on moving platforms and/or randomly distributed sensors. In this paper, we present a 3D integral imaging method with unknown sensor positions. In the proposed method, all the sensors are randomly distributed on a plane with parallel optical axes. More, only the relative position of any two sensors is needed whereas all other sensor positions are unknown. We combine image correspondences extraction, camera perspective model, two view geometry and computational integral imaging D reconstruction techniques to estimate the unknown sensor positions and reconstruct 3D images. The experiment results executed both in lab and outside show the feasibility of the proposed method in 3D integral imaging. Furthermore, the experiments indicate that the quality of reconstructed images by using the proposed sensor position estimation algorithm can be improved compared to the ones by using the physical measurements of the sensor positions.
- [Show abstract] [Hide abstract] ABSTRACT: Three-dimensional (3-D) optical image sensing and visualization technologies have been researched extensively for different applications in fields as diverse as entertainment, medical sciences, robotics, manufacturing, and defense. In many instances, the capabilities of 3-D imaging and display systems have revolutionized the progress of these disciplines, enabling new detection/display abilities that would not have been otherwise possible. As one of the promising methods in the area of 3-D sensing and display, integral imaging offers passive and relatively inexpensive way to capture 3-D information and to visualize it optically or computationally. The integral imaging technique belongs to the broader class of multiview imaging techniques and is based on a century old principle which has only been resurrected in the past decade owing to advancement of optoelectronic image sensors as well as the exponential increase in computing power. In this paper, historic and physical foundations of integral imaging are overviewed; different optical pickup and display schemes are discussed and system parameters and performance metrics are described. In addition, computational methods for reconstruction and range estimation are presented and several applications including 3-D underwater imaging, near infra red passive sensing, imaging in photon-starved environments, and 3-D optical microscopy are discussed among others.
- [Show abstract] [Hide abstract] ABSTRACT: Recovering 3D object information through analyzing image focus (or defocus) has been shown to be a potential tool in situations where only a single viewing point is possible. Precise modeling and manipulation of imaging system parameters, e.g. depth of field, modulation transfer function and sensor characteristics, as well as lighting condition and object surface characteristics are critical for effectiveness of such methods. Sub-optimal performance is achieved when one or more of these parameters are dictated by other factors. In this paper, we will discuss the implicit requirements imposed by most common depth from focus/defocus (DFF/DFD) analysis methods and offer related application considerations. We also describe how a priori information about the objects of interest can be used to improve performance in realistic applications of this technology.
- [Show abstract] [Hide abstract] ABSTRACT: Conventional multiview imaging systems commonly utilize a planar lenslet array and a rigid, flat image sensor in the pickup stage to capture different views of the scene. In this Letter, we remove this constraint by proposing the concept of three-dimensional (3D) imaging with detector arrays that may conform to arbitrarily shaped surfaces or platforms. A nonplanar detector array configuration can be used in combination with a flexible lenslet array to capture different views. The orientation and optical axes of individual image sensing elements could vary. A point-by-point 3D reconstruction algorithm is described and the feasibility of the proposed approach is demonstrated through simulated imagery.
- [Show abstract] [Hide abstract] ABSTRACT: In this chapter we present three types of microscopy-related configurations while the first one is used for 3-D movement monitoring of the inspected samples, the second one is used for super-resolved 3-D imaging, and the last one presents an overview digital holographic microscopy applications. The first configuration is based on temporal tracking of secondary reflected speckles when imaged by properly defocused optics. We validate the proposed scheme by using it to monitor 3-D spontaneous contraction of rat’s cardiac muscle cells while allowing nanometric tracking accuracy without interferometric recording. The second configuration includes projection of temporally varying speckle patterns on top of the sample and by proper decoding exceeding the diffraction as well as the geometrical-related lateral resolution limitation. In the final part of the chapter, we overview applications of digital holographic microscopy (DHM) for real-time non-invasive 3-D sensing, tracking, and recognition of living microorganisms such as single- or multiple-cell organisms and bacteria.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, the 3D integral imaging method is extended to situations where the sensor positions in the image pick up stage are unknown. Conventional integral imaging systems require a priori knowledge of sensor positions in the image capture stage which can be difficult to measure in synthetic aperture or randomly distributed sensors modes. In the proposed method, only the relative position of two sensors is needed whereas all other sensors positions are unknown. We combine image correspondences extraction, camera perspective model, two view geometry and computational integral imaging D reconstruction techniques to overcome this limitation in integral imaging systems. The image reconstruction quality of the system with unknown sensor positions is compared with conventional integral imaging with known sensor positions. We also demonstrate how the proposed method may be used to improve the image reconstruction quality even in situations where the sensor positions recorded are subject to measurement errors .
- [Show abstract] [Hide abstract] ABSTRACT: Three dimensional (3D) imaging systems have been recently suggested for passive sensing and recognition of objects in photon-starved environments where only a few photons are emitted or reflected from the object. In this paradigm, it is important to make optimal use of limited information carried by photons. We present a statistical framework for 3D passive object recognition in presence of noise. Since in quantum-limited regime, detector dark noise is present, our approach takes into account the effect of noise on information bearing photons. The model is tested when background noise and dark noise sources are present for identifying a target in a 3D scene. It is shown that reliable object recognition is possible in photon-counting domain. The results suggest that with proper translation of physical characteristics of the imaging system into the information processing algorithms, photon-counting imagery can be used for object classification.
- [Show abstract] [Hide abstract] ABSTRACT: Optofluidic devices offer flexibility for a variety of tasks involving biological specimen. We propose a system for three-dimensional (3D) sensing and identification of biological micro-organisms. This system consists of a microfluidic device along with a digital holographic microscope and relevant statistical recognition algorithms. The microfluidic channel is used to house the micro-organisms, while the holographic microscope and a CCD camera record their digital holograms. The holograms can be computationally reconstructed in 3D using a variety of algorithms, such as the Fresnel transform. Statistical recognition algorithms are used to analyze and identify the micro-organisms from the reconstructed wavefront. Experimental results are presented. Because of computational reconstruction of wavefronts in holographic imaging, this technique offers unique advantages that allow one to image micro-organisms within a deep channel while removing the inherent microfluidic-induced aberration through interferometery.
- [Show abstract] [Hide abstract] ABSTRACT: The paper presents the application of digital holography microscopy (DHM) for non-invasive realtime 3D sensing, recognition, and tracking of microorganisms such as cells without the need for staining or destroying the cells. 3D optical imaging and information photonics provide a rich content for applying different mathematical methods for detection and recognition of biological microorganisms, and the applications range from detection of diseased cells, marker-less cell sorting, pathogen identification, etc.
- [Show abstract] [Hide abstract] ABSTRACT: Real-time high-throughput identification, screening, characterization, and processing of biological specimen is of great interest to a host of areas spanning from cell biology and medicine to security and defense. Much like human biometrics, microorganisms exhibit natural signatures that can be used for identification. In this paper, we first overview two optical techniques, namely digital holographic microscopy and holographic optical tweezers which can non-invasively image, manipulate, and identify microorganisms in three dimensions. The two methods bear similarities in their optics and implementation. Thus, we have proposed a new approach to identification of micro/nano organisms and cells by combining the two methods of digital holographic microscopy and holographic optical tweezers which can be integrated into a single compact hardware. The proposed system can simultaneously sense, control, identify, and track cells and microorganisms in three dimensions. New possibilities that arise from the proposed method are discussed.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, we investigate an optical-trap-based method for the detection of structural changes of the red blood cell (RBC) membrane affected by Ca<sup>2+</sup> ions. Individual cells are immobilized by the use of optical tweezers and are monitored live, while the concentration of Ca<sup>2+</sup> ions in the buffer is changed simultaneously. Ca<sup>2+</sup> ions are known to affect the cells' membrane morphology. These changes are attributed to the formation of calcium-induced hydrophobic aggregates of phospholipid molecules in the RBC membrane, resulting in a net change in membrane rigidity. Membrane deformation results in the change of effective radius and the drag coefficient of the cell, both of which affect the Brownian motion of the cell in solution. This motion is indirectly measurable by monitoring the forward scattering light and its dependence on the size and drag coefficient of the cell. We show the relationship between the Ca<sup>2+</sup> ion concentration and the optical trap specifications. The results are in agreement with previous biological studies and the phase contrast observations of living RBCs under investigation.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper we present an overview of our work on a method to provide three-dimensional (3D) identification and tracking of biological micro/nano-organisms. This approach connects digital holographic microscopy and statistical methods for cell identification. For 3D data acquisition of living biological microorganisms, a filtered white light source, LED or laser diode beam propagates through a biological microorganism and the transversely and longitudinally magnified Gabor hologram pattern of the biological microorganism by microscope objective is optically recorded with a CCD camera interfaced with a computer. D imaging of the biological microorganism from the magnified Gabor hologram pattern is obtained by applying the computational Fresnel propagation algorithm. For identification and tracking of the biological microorganism, statistical approaches based on statistical estimation and inference algorithms are developed to the segmented holographic 3D image. Overviews of analytical frameworks are discussed and experimental results are presented.
- [Show abstract] [Hide abstract] ABSTRACT: This work investigates an optical trap based method for detection of structural changes of the red blood cell (RBC) membrane affected by Ca2+ ions. Individual cells are immobilized by use of optical tweezers and are monitored live while the concentration of Ca2+ ions in the buffer is changed simultaneously. Ca2+ ions affect cells' membrane morphology, which results in the change of effective radius as well as drag coefficient of the cell, both of which affect the Brownian motion of the cell in solution. This motion is measurable indirectly by tracking the forward scattering light and its dependence on size and drag coefficient of the cell. We show the relationship between Ca2+ ion concentration and optical trap specifications.
- [Show abstract] [Hide abstract] ABSTRACT: We briefly overview applications of digital holographic microscopy (DHM) for real-time non-invasive three dimensional sensing, tracking, and recognition of living microorganisms such as single/multiple cell organisms, bacteria, etc. Analytical frameworks and experimental results are presented.
- [Show abstract] [Hide abstract] ABSTRACT: Three-dimensional (3D) imaging systems are being researched extensively for purposes of sensing and visualization in fields as diverse as defense, medical imaging, art, and entertainment. An overview on a multi-view imaging system in an axially distributed sensing architecture for three dimensional is presented. In this configuration, the sensor moves along its optical axis and collects 2D imagery which can be computationally reconstructed at arbitrary depths in the object space. When compared to traditional 2D imaging techniques, D imaging offers advantages in ranging, robustness to scene occlusion, and target recognition performance. The proposed imaging system is different than conventional multiview imaging systems, such as integral imaging, in the sense that collection of 3D information is not uniform across the field of view and in many cases the inherent linear motion of the platform can be exploited for 3D image acquisition. The system parameters are analyzed and experimental results are presented.