Abstract: Many applications in non-destructive testing at a microscopic level and in live cell imaging require automated focusing due to unstable environmental conditions, moving specimen or the limited depth of field of the applied optical imaging systems. Digital holography permits the recording and the numerical reconstruction of optical wave fields in amplitude and phase. This enables imaging of multiple focal planes from a single recorded hologram without mechanical realignment. The combination of numerical refocusing with image sharpness quantification algorithms yields subsequent autofocusing. With calibrated optical imaging systems this feature can be used also to determine the position and axial displacements of a sample. In order to show the application potential of digital holographic autofocusing in microscopy the method and results from investigations on several amplitude and phase objects are reviewed. This includes a demonstration of the reliability of automated refocusing, multi-focus quantitative phase contrast imaging of suspended cells, refocusing of quantitative phase contrast images during the analysis of the temporal dependency of cell spreading on surfaces and the quantification of toxin mediated morphological cell alterations during long-term observations. It is also shown for the example of sedimenting red blood cells that the method can be applied for minimally-invasive tracking of multiple particles. Finally, the usage of numerical autofocus for quantitative migration analysis of arbitrary shaped cells in a three-dimensional collagen matrix is demonstrated.

Abstract: A demonstration of the capabilities of Digital Holography (DH) in microscope configuration is presented for inspecting and qualifying optical microstructures. Different structures with dimensions ranging from hundreds to few tens of microns are investigated, analyzed and characterized by DH showing that the technique is suitable either for liquid as well as polymeric microlenses. Thanks to the numerical reconstruction of the complex wavefields, we show that DH is able to retrieve not only the morphology of each single structure element but also to furnish accurate information on all the changes (spontaneous or induced) occurring during the inspection time, such as the curvature variation of liquid microlenses or the wavefront distortion.

Abstract: In video conferences, one user can either look at the remote image of the other captured by a video camera, or look at the camera that is capturing her/him, but not two tasks at the same time. The lack of eye contact caused by this misalignment substantially reduces the effectiveness of communication with an unpleasant feeling of disconnectedness. We propose an approach to bring eye contact back while user looks at the remote image of the other by a novel system composed by a Time-of-Flight depth sensor and traditional stereo. The key success of this system is to faithfully recover scene's depth. In this 2.5D space, the controlling of the user's eye-gaze becomes relatively easier. To evaluate the performance of the system, we conducted two user studies. One focuses on subjects have been trained to be familiar to eye gaze displayed in images; another is blind evaluation that subjects have no prior knowledge about eye gaze. Both evaluations show that the system can bring desktop participants closer to each other.

Abstract: This paper addresses the disocclusion problem which may occur when using Depth-Image-Based Rendering (DIBR) techniques in 3DTV and Free-Viewpoint TV applications. A new DIBR technique is proposed, which combines three methods: a Joint Projection Filling (JPF) method to handle disocclusions in synthesized depth maps; a backward projection to synthesize virtual views; and a full-Z depth-aided inpainting to fill in disoccluded areas in textures. The JPF method performs the pixels warping for virtual depth map synthesis while making use of an occlusion-compatible pixel ordering strategy, to detect cracks and disocclusions, and to select the pixels to be propagated in the occlusion areas filling process. The full-Z depth-aided inpainting method fills in disocclusions with textures at the correct depth, preserving the boundaries of the objects. Ghosting artifacts, which might otherwise result from pixel projections, are here avoided by introducing a confidence measure on background pixels to be used in the JPF process.

Abstract: In this paper, a novel three-dimensional (3-D) integral imaging system to simultaneously improve the depth-of-focus (DOF) and the resolution of the reconstructed object images by using the non-uniform lenslet array and the intermediate-view reconstruction technique (IVRT) is proposed. That is, by using the non-uniform lenslets, DOF-enhanced integral images of 3-D objects can be picked up, and then by applying the IVRT to these picked-up integral images, resolution as well as DOF-enhanced object images can be reconstructed. To show the feasibility of the proposed system, experiments with test objects are performed and the results are discussed.

Abstract: in this paper a simulator of a multi-view shooting system with parallel optical axes and structurally variable configuration is proposed. The considered system is dedicated to the production of 3D contents for auto-stereoscopic visualization. The global shooting/viewing geometrical process, which is the kernel of this shooting system, is detailed and the different viewing, transformation and capture parameters are then defined. An appropriate perspective projection model is afterward derived to work out a simulator. At first, this latter is used to validate the global geometrical process in the case of a static configuration. Next, the simulator is used to show the limitations of a static configuration of this shooting system type by considering the case of dynamic scenes and then a dynamic scheme is achieved to allow a correct capture of this kind of scenes. After that, the effect of the different geometrical capture parameters on the 3D rendering quality and the necessity or not of their adaptation is studied. Finally, some dynamic effects and their repercussions on the 3D rendering quality of dynamic scenes are analyzed using error images and some image quantization tools. Simulation and experimental results are presented throughout this paper to illustrate the different studied points. Some conclusions and perspectives end the paper.

Abstract: This paper presents a full-body volumetric reconstruction of a person in a scene using a sensor network, where some of them can be mobile. The sensor network is comprised of couples of camera and inertial sensor (IS). Taking advantage of IS, the 3D reconstruction is performed using no planar ground assumption. Moreover, IS in each couple is used to define a virtual camera whose image plane is horizontal and aligned with the earth cardinal directions. The IS is furthermore used to define a set of inertial planes in the scene. The image plane of each virtual camera is projected onto this set of parallel-horizontal inertial-planes, using some adapted homography functions. A parallel processing architecture is proposed in order to perform human real-time volumetric reconstruction. The real-time characteristic is obtained by implementing the reconstruction algorithm on a graphics processing unit (GPU) using Compute Unified Device Architecture (CUDA). In order to show the effectiveness of the proposed algorithm, a variety of the gestures of a person acting in the scene is reconstructed and demonstrated. Some analyses have been carried out to measure the performance of the algorithm in terms of processing time. The proposed framework has potential to be used by different applications such as smart-room, human behavior analysis and 3D teleconference.

Abstract: In this paper, we explore the 3D structure of light scattering from dark-field illuminated live 3T3 cells in the presence of 40 nm gold nanomarkers. For this purpose, we use a high resolution holographic microscope combining the off-axis heterodyne geometry and the phase-shifting acquisition of the digital holograms. A comparative study of the 3D reconstructions of the scattered fields allows us to locate the gold markers which yield, contrarily to the cell structures, well defined bright scattering patterns that are not angularly titled and clearly located along the optical axis (z). This characterization is an unambiguous signature of the presence of gold biological nanomarkers, and validates the capability of digital holographic microscopy to discriminate them from background signals in live cells.

Abstract: In this study, we have exploited the parallel nature of the computations involved in the process of digital holography using novel look-up table method. We utilize CUDA enabled GPU to accelerate each step of the digital holography, i.e. preparation of the principle fringe patterns, hologram synthesis by accessing and superimposing the appropriate principal fringe patterns and finally the optical reconstruction at various depths. The proposed method was tested for a simple 3D object consisting of many points located at different depths and compared to that of the CPU. Our simulation results confirm that the GPU implementation is much faster than that of the CPU.

Abstract: This work presents a novel physical mean scheme for correcting the image curvatures introduced by a micro-objective (MO) lens in digital holographic microscopy (DHM). The image curvature due to the quadratic phase term is commonly referred to as defocus aberration. An offset lens is also developed to compensate for the defocus aberration of an MO, allowing us to remove the image curvatures. The proposed scheme is characterized by the separation of the MO and offset lens, ensuring that their foci are common. Analysis results of the optical operator method indicate that the inverted and magnified object wavefront, having passed through the modified microscopic configuration, no longer carries and contains the wavefront curvature due to MO. The proposed scheme is implemented based on arbitrary two-step phase-shift interferometry (PSI), yet with an unknown phase step. Hence, the numerical algorithm can subtract and eliminate the undesired terms, i.e. zero-order and twin-image terms, which inevitably arise from holographic recording. Additionally, the effect of the image curvatures are compared and demonstrated without and with the proposed on-axis setup. Experimental results indicate that the proposed scheme can remove the image curvatures from the defocus aberration due to MO, ultimately enhancing the phase contrast reconstructed image.

Abstract: Photon-counting sensing has been widely used in low-light level imaging applications. Photon-counting images can be processed in a simpler and faster manner especially when the binary photon numbers are considered. In this paper, a distance extraction method with stereoscopic photon-counting passive sensing is proposed. Distance extraction is carried out with a stereoscopic photon counting image pair. Nonlinear correlation obtains horizontal discrepancy that maximizes the similarity between two rectified photon-counting images. Computer experiments confirm that the proposed method can extract distance information to an object under low-light level conditions. Performance is evaluated by mean and variance of distance obtained with varying expected number of photons in the scene.

Abstract: It is well established that synthetic aperture (SA) generation allows superresolved imaging. This is particularly important in digital holographic microscopy when ones want to retain either large object field of view or long working distance (or both) while maintaining a reasonable resolution limit. In this contribution, we show synthetic aperture superresolution (SASR) by interferometric imaging and analyze its capabilities considering object's edge processing. In a first proof-of-principle approach, we introduce the principles of edge enhancement by SASR. In a second method we provide two-dimensional (2-D) border analysis by SASR and comparison with other methods for edge processing. Finally, a third approach is presented regarding image edge processing of biological samples.

Abstract: This paper presents a novel system that is fusing efficient and state-of-the-art techniques of stereo vision and machine learning, aiming at object detection and recognition. To this goal, the system initially creates depth maps by employing the Graph-Cut technique. Then, the depth information is used for object detection by separating the objects from the whole scene. Next, the Scale-Invariant Feature Transform (SIFT) is used, providing the system with unique object's feature key-points, which are employed in training an Artificial Neural Network (ANN). The system is then able to classify and recognize the nature of these objects, creating knowledge from the real world.

Abstract: The year 2010 may be recorded as a first year of successful commercial 3D products. Among them, the 3D LCD TVs are expected to be the major one regarding the sales volume. In this paper, the principle of current stereoscopic 3D LCD TV techniques and the required flat panel display (FPD) technologies for the realization of them are reviewed.

Abstract: A high resolution micro computed tomography (micro-CT) system for live small animal imaging has been developed. The system consists of an x-ray source with micro focus spot and high brightness, rotating gantry with a x-ray tube and flat panel detector pair and a stationary and a horizontally positioned small animal bed to achieve a conebeam mode scan. The system is optimized for in vivo small animal imaging and the capability of administering respiratory anesthesia during scanning. The Feldkamp algorithm was adopted in image reconstruction with graphic processing unit (GPU). We evaluated the spatial resolution, image contrast, and uniformity of system using phantom. As the result, the spatial resolution of the system was the 56lp/mm at 10% of the MTF curve, and the radiation dose to the sample was 98mGy. The minimal resolving contrast was found to be less than 46 CT numbers on low-contrast phantom. We present the image test results of the bone and lung, and heart of the live mice.

Abstract: Digital holography is an attractive method for instantaneous measurement of three-dimensional (3D) objects and numerical reconstruction of the 3D objects after the recording. The reconstruction can be implemented optically for visualization. In this paper, we review a 3D measurement system based on phase-shifting digital holography and an optical 3D reconstruction based on wavefront modulation. In the 3D reconstruction, phase distribution is used for 3D reconstruction because there is no available spatial light modulator that can modulate both amplitude and phase. The viewing zone is limited by the pixel size of phase-mode spatial light modulator. For enlargement of viewing zone, we have proposed a timesharing method to distribute the reconstructed 3D object in wide area by using a Galvanometer mirror. Numerical and experimental results are presented.

Abstract: On-axis projection of a-priori known axially varying patterns can be used for three dimensional (3-D) imaging. However, this method can only distinguish between a discrete number of axial planes. In this work, an inter-planar interpolation method is used to estimate the distance by a-priori knowledge about the pattern's compatible axial range. The method is based on the use of three predefined correlation based parameters of the image reflected from the object. The use of several parameters improves the interpolation precision leading to an improved 3-D estimation. An experimental setup was built using a spatial light modulator (SLM) which implements a desired phase element that forms the axially varying projected pattern. The experimental results match the expected behavior foreseen via numerical simulations.

Abstract: Autostereoscopic 3DTV is becoming an exciting media that enable us to view a 3D scene from more than one viewpoint. Meanwhile, considered as the ultimate autostereoscopic 3DTV, Free-viewpoint TV (FTV) can provide arbitrary views by freely synthesizing and changing viewpoints. Essentially, either 3DTV or FTV is based on virtual view synthesis using captured views along with corresponding depth information. In this paper, we study how virtual views can be reliably generated from multiple captured videos for 3D display. One key challenge is that the required depth information may contain depth errors, leading to uncomfortable artifacts in the synthesized view. We review the recent progress in virtual view synthesis methods where depth reliability is considered to handle synthesis artifacts and improve the quality of the virtual view. Not only for intermediate virtual view, have we also presented high-quality close-up view synthesis methods for wider navigation in 3DTV and FTV.

Abstract: In this work, a blue light-emitting diode (LED) is used in lenseless Digital In-line Holography Microscopy (DIHM) to show that micrometre resolution can be reached even when millimetre range objects, such as the head of a fruit fly, are imaged with partially coherent spherical wavefronts. The influence of the spatial coherence on the resolution of the microscope is analysed by changing the diameter of pinhole from which the spherical wavefronts are originated. Even though the best achieved resolution with the use of the LED is less than the ultimate provided by the use of fully coherent laser sources, the former is very competitive as the ratio performance/cost is compared for both approaches. Micrometre-sized beads are used for quantitative testing of the lateral resolution.

Abstract: According to IEEE 802.15.4a standardization, an ultra wideband PHY symbol is capable of carrying two bits of information and only one pulse shall be transmitted in each symbol. To prevent inter symbol interference caused by multipath effect, the guard interval is present between the possible burst positions. In order to make full use of the symbol for estimating the azimuth and the elevation of target, we can add additional information at the guard interval position, if the pulse used at the possible burst position is different from the pulse used at the guard interval position. Using the orthonormality between the multiple pulses, furthermore, inter symbol interference can be avoided at the correlation receiver. In this paper, as the first step for estimating the azimuth and the elevation information, we propose a novel PHY symbol structure for IR-UWB system based on IEEE 802.15.4a standardization and orthogonal pulses to enhance the data rates without the bit-error-rate (BER) performance degradation. In the proposed scheme, the pulse used at the possible burst position is the modified hermite polynomial (MHP) pulse of order n equal to 3 and the pulse used at guard interval position is the MHP pulse of order n equal to 4. The performance of the proposed structure is evaluated by computer simulations over the IEEE 802.15.4a channel model. Simulation results show that the proposed symbol structure with orthogonal pulses can double the data rates of the systems without BER performance degradation.

Abstract: Digital holographic microscopy is a quantitative phase measurement technique that can provide nanometer resolution of the thickness or surface profile of an object. We analyze the influence of additive noise in the hologram plane on the accuracy of phase measurement. We analyze Gaussian distributed and Poisson distributed shot noise in the camera plane and we develop a model for quantifying the phase error in the reconstructed phase.

Abstract: This paper provides an introduction to photometric methods for image-based 3D shape reconstruction and a survey of photometric stereo techniques. We begin with taxonomy of active and passive shape acquisition techniques. Then we describe the methodical background of photometric 3D reconstruction, define the canonical setting of photometric stereo (Lambertian surface reflectance, parallel incident light, known illumination direction, known surface albedo, absence of cast shadows), discuss the 3D reconstruction of surfaces from local gradients, summarize the concept of the bidirectional reflectance distribution function (BRDF), and outline several important empirically and physically motivated reflectance models. We provide a detailed treatment of several generalizations of the canonical setting of photometric stereo, namely non-distant light sources, unknown illumination directions, and, in some detail, non-Lambertian surface reflectance functions. An important special case is purely specular reflections, where an extended light source allows capturing a surface that consists of perfectly specular surface patches. Linear combinations of purely Lambertian and purely specular reflectance components are favorably used for reconstructing smooth surfaces and also human skin. Nonuniform surface reflectance properties are estimated based on a simultaneous 3D reconstruction and determination of the locally variable parameters of the reflectance function based on a multitude of images. Assuming faceted surfaces, the effective resolution of the 3D reconstruction result can be increased to some extent beyond that of the underlying images. Other approaches separate specular and diffuse reflectance components based on polarization data or color information. The specular reflections can be used additionally to estimate the direction from which the surface is illuminated. Finally, we describe methods to combine photometric 3D reconstruction techniques with active and passive triangulation-based approaches.

Abstract: We apply multiple-wavelength digital holography in combination with epi-fluorescence microscopy in order to generate quantitative phase and fluorescence information from cell samples. While digital holography provides high precision morphological information, the addition of fluorescence supplies the specificity needed to identify cellular constituents. By the application of multiple-wavelength digital holography it is possible to obtain the complete wavefront data deterministically and in real-time. We demonstrate this dual-mode imaging capability through the investigation of living cells.