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This paper presents a novel approach to capture light field in camera arrays based on the compressive sensing framework. Light fields are captured by a linear array of cameras with overlapping field of view. In this work, we design a redundant dictionary to exploit cross-cameras correlated structures to sparsely represent cameras image. Our main contributions are threefold. First, we exploit the correlations between the set of views by making use of a specially designed redundant dictionary. We show experimentally that the projection of complex scenes onto this dictionary yields very sparse coefficients. Second, we propose an efficient compressive encoding scheme based on the random convolution framework [1]. Finally, we develop a joint sparse recovery algorithm for decoding the compressed measurements and show a marked improvement over independent decoding of CS measurements.

Human observers group local shading patterns into global super-patterns that appear to be illuminated in some unitary fashion. Many years ago, this was noticed for the case of uniform, unidirectional illumination. Recently, we found that it also applies to convergent and divergent illumination flows, but that human observers are blind to rotational light flow patterns (in the sense of being unable to group the local shading patterns). We now report that human observers are also blind to deformation patterns. This is perhaps interesting because convergent, divergent, rotational, and deformation patterns all occur in natural light fields. This is an idiosyncrasy of the human visual system, on par with the fact that visual awareness fails to present the observer with saddle shapes. ispartof: i-Perception vol:3 issue:7 pages:467-480 ispartof: location:United States status: published

Computation of a binary spatial light modulator (SLM) pattern that generates a desired light field is a challenging quantization problem for which several algorithms have been proposed, mainly for far-field or Fourier plane reconstructions. We study this problem assuming that the desired light field is synthesized within a volumetric region in the non-far-field range after free space propagation from the SLM plane. We use Fresnel and Rayleigh-Sommerfeld scalar diffraction theories for propagation of light. We show that, when the desired field is confined to a sufficiently narrow region of space, the ideal gray-level complex-valued SLM pattern generating it becomes sufficiently low pass (oversampled) so it can be successfully halftoned into a binary SLM pattern by solving two decoupled real-valued constrained halftoning problems. Our simulation results indicate that, when the synthesis region is considered, the binary SLM is indistinguishable from a lower resolution full complex gray-level SLM. In our approach, free space propagation related computations are done only once at the beginning, and the rest of the computation time is spent on carrying out standard image halftoning. (C) 2011 Optical Society of America

From a theoretical point of view, the use of the shading cue involves estimates of the light field and thus observers need to judge the light field and the shape simultaneously. The conventional stimulus in perceptual experiments, a circular disk filled with a monotonic gradient on a uniform surround, represents a local shading or tonal gradient. In typical scenes, such gradients vary smoothly from point to point over large areas, whereas light fields are globally defined and tend to be invariant over large parts of the scene. Hence, it is hardly surprising that multi-local shape estimates tend to synchronize although previous reports of such synchronies involved uniform, homogeneous light fields. Here, we consider more complicated and more realistic light fields. We present extensive, highly structured, quantitative observations using novel paradigms. Human observers are able to deal with some structured light fields but totally fail in others, even though these may be formally similar (like radial and circular fields). Observers respond very differently in some cases where the light fields differ only by sign, like converging and diverging fields. These results can be qualitatively understood on the basis of a few simple assumptions, mainly global top-down template matching of peripheral local data.

A method for practical area upscaling of nanopatterning for light-harvesting and photocatalytic applications is presented. Large area electron beam lithography is used to design patterns of simple-...

The effect of incident light field ellipticity on the electromagnetically induced absorption (EIA) and electromagnetically induced transparency (EIT) resonances has been studied experimentally and computationally in Hanle configuration with longitudinal and transverse magnetic fields. We identify the Zeeman coherences that influence the resonance profile and study the role of coherence-transfer from excited to ground state via spontaneous emission as a function of ellipticity for the F{sub g}=2{yields}F{sub e}=3 transition of {sup 87}Rb. The EIT resonance observed with the light field locked on the F{sub g}=1{yields}F{sub e}=2 transition of {sup 87}Rb is an influence of the nearby F{sub g}=1{yields}F{sub e}=0 closed and F{sub g}=1{yields}F{sub e}=1 open transitions. With increase in ellipticity the observed EIA and EIT resonances diminish in amplitude for a longitudinal magnetic field and are enhanced for a transverse magnetic field. We computationally account for these observations and discuss the factors that influence the EIA and EIT resonance amplitudes as a function of ellipticity and show that for a transverse field scan the ellipticity dependence of the EIA resonance amplitude can be accounted for without invoking the Doppler effect unlike for a longitudinal field scan. We also show that the maximum in the EIA resonance amplitude obtained for nonzeromore » ellipticities with a longitudinal magnetic field depends on the closedness of the atomic system.« less

While the creation of three-dimensional models from real-life objects is a commonly applied process, the reconstruction of complete datasets from such objects is still a delicate task. In this paper, a simple yet powerful framework is proposed that is able to reconstruct both geometry and appearance of a given object interactively. Working in an incremental mode of operation, it enables the user to reconstruct a given scene with full visual feedback during the progress of the reconstruction process. For geometry reconstruction, an existing surface reconstruction algorithm has been investigated and adjusted to the needs of the framework. Furthermore, a hardware-accelerated surface light field algorithm has been integrated into the framework that performs appearance reconstruction of the object. The target application of our framework is the reconstruction of real-life objects using mobile acquisition devices. We demonstrate the performance and usefulness of our framework by reconstructing models from previously acquired datasets of real-life objects. Furthermore, we provide results of experiments run in our own model acquisition setup.

Date of Conference: 22-24 April 2010 One of the important techniques used for three dimensional television (3DTV) is holography. In holographic 3DTV, spatial light modulators (SLM) are used as the display device. SLMs that provide the most limited modulation are the binary SLMs, since only two different values can be assigned to their pixels. An important signal processing problem arising here is the determination of the binary signal to be written on the SLM among the possible ones such that the desired light field is generated to the best extent. Many of the proposed methods do not produce satisfactory results in terms of error rate, computational performance or light efficiency. We propose an optical setup to be placed in front of the binary SLM and the associated signal processing algorithm. The proposed system uses a 4-f setup and a periodic mask is placed to the Fourier plane. As a result, the binary SLM is convolved with a series of regularly spaced impulse functions and we get a new SLM which is smaller in pixel count compared to binary SLM but which can provide 16-bit full complex modulation. It becomes easier to generate the desired light field with this new SLM. Also, the required computations are carried out in a fast manner to enable real-time operation. ©2010 IEEE.

Image based lighting, (IBL), is a computer graphics technique for creating photorealistic renderings of synthetic objects such that they can be placed into real world scenes. IBL has been widely recognized and is today used in commercial production pipelines. However, the current techniques only use illumination captured at a single point in space. This means that traditional IBL cannot capture or recreate effects such as cast shadows, shafts of light or other important spatial variations in the illumination. Such lighting effects are, in many cases, artistically created or are there to emphasize certain features, and are therefore a very important part of the visual appearance of a scene. This thesis and the included papers present methods that extend IBL to allow for capture and rendering with spatially varying illumination. This is accomplished by measuring the light field incident onto a region in space, called an Incident Light Field, (ILF), and using it as illumination in renderings. This requires the illumination to be captured at a large number of points in space instead of just one. The complexity of the capture methods and rendering algorithms are then significantly increased. The technique for measuring spatially varying illumination in real scenes is based on capture of High Dynamic Range, (HDR), image sequences. For efficient measurement, the image capture is performed at video frame rates. The captured illumination information in the image sequences is processed such that it can be used in computer graphics rendering. By extracting high intensity regions from the captured data and representing them separately, this thesis also describes a technique for increasing rendering efficiency and methods for editing the captured illumination, for example artificially moving or turning on and of individual light sources.

We present a practical and inexpensive approach for the acquisition and rendering of static incident light fields. Incident light fields can be used for lighting virtual scenes or to insert virtual objects into real world video footage. The virtual objects are correctly lit and cast shadows in the same way as real objects in the scene. We propose to use an inexpensive planar mirror and a high dynamic range video camera to record incident light fields quickly, making our method suitable for outdoor use. The mirror serves as a moving virtual camera sampling the light field. To render with the acquired data we propose a hardware accelerated rendering algorithm that reproduces the complex lighting and shadows of the 4D light field. The algorithm is scalable and allows continuous trade between quality and rendering speed.

Date of Conference: 8-11 Oct. 2006 Conference name: 2006 International Conference on Image Processing Two important signal processing problems in the display side of a holographic 3DTV are the computation of the diffraction field of a 3D object from its abstract representation, and determination of the best display configuration to synthesize some intended light distribution. To solve the former problem, we worked on the computation of ID diffraction patterns from discrete data distributed over 2D space. The problem is solved using matrix pseudo-inversion which dominates the computational complexity. Then, the light field synthesis problem by a deflectable mirror array device (DMAD) is posed as a constrained linear optimization problem. The formulation makes direct application of common optimization algorithms quite easy. The simulations indicate that developed methods are promising. ©2006 IEEE.

This paper presents a light field rendering framework based on matrix optics. Matrix optics, in contrast to intersection-based methods such as ray-tracing, has the advantage that a generic series of optic operators can be combined into a single matrix. This enables us to realize a “virtual optical bench” where different setups can be easily tested. We introduce the theoretical foundation of matrix optics and define a set of operators suitable for light fields. We then discuss a wavelet compression scheme for our light field representation. Finally we introduce a real-time rendering approach based on matrix optics suitable for both uncompressed and compressed light fields.

Realistic image synthesis requires both complex and realistic models of real-world light sources and efficient rendering algorithms to deal with them. In this paper, we describe a processing pipeline for dealing with complex light sources from acquisition to global illumination rendering. We carefully design optical filters to guarantee high precision measurements of real-world light sources. We discuss two practically feasible setups that allow us to measure light sources with different characteristics. Finally, we introduce an efficient importance sampling algorithm for our representation that can be used, for example, in conjunction with Photon Maps.

International audience; Interactive visualization of complex, real-world light sources has so far not been feasible. In this paper, we present an hardware accelerated direct lighting algorithm based on a recent high quality light source acquisition technique. By introducing an approximate reconstruction of the exact model, a multi-pass rendering approach, and a compact data representation, we are able to achieve interactive frame rates. The method is part of the processing pipeline from light source acquisition to high quality lighting of a virtual world.

[EN]We demonstrate a tri-wavelength laser generation from a Nd-doped calcium niobium gallium garnet disordered crystal waveguide. The laser threshold obtained was 83 mW of launched pumping laser corresponding to a slope efficiency of 5.1%. According to the laser spectrum, the output light was found to be a tri-wavelength laser, with wavelengths of 1058 nm, 1060 nm and 1064 nm, respectively. The stability of the output laser was investigated, which found that the output laser was a continuous laser., This work was carried out under the support by the National Natural Science Foundation of China (No. 11274203), the Spanish Ministerio de Ciencia e Innovación (projects CSD2007-00013 and FIS2009-09522), and the Junta de Castilla y León (project SA086A12-2). Yang Tan acknowledges the support by the Independent Innovation Foundation of Shandong University (IIFSDU, No. 104222012GN056 / 11160072614098) and China Postdoctoral Science Foundation (Grant No. 2013M530316).

We try to find out the details of how light fields behind the structures of photomasks develop in order to determine the best conditions and designs for proximity printing. The parameters that we use approach real situations like structure printing at proximity gaps of 20 to 50 mm and structure sizes down to 2 mm. This is the first time that an experimental analysis of light propagation through a mask is presented in detail, which includes information on intensity and phase. We use high-resolution interference microscopy (HRIM) for the measurement. HRIM is a Mach-Zehnder interferometer, which is capable of recording three-dimensional distributions of intensity and phase with diffraction-limited resolution. Our characterization technique allows plotting the evolution of the desired light field, usually called the aerial image, and therefore gives access to the printable structure until the desired proximity gap. Here, we discuss in detail the evolution of intensity and phase fields of elbow or corner structures at different positions behind a phase mask and interpret the main parameters. Of particular interest are tolerances against proximity gap variation and the theoretical explanation of the resolution in printed structures.

Light fields are a computer graphics modeling technique that represents objects using radiance samples instead of geometry. Radiance samples may be stored as sets of images or 4D arrays of pixel values. Light fields have various advantages: their rendering complexity only depends on the output image’s, they can represent sophisticated illumination effects, and they are well-suited for display using autostereoscopic devices. To study different light-field representations, as well as their capture, generation, resampling, storage, composition, rendering and display, we have developed a light-field based API and graphics system. The system supports models based on different light-field parameterizations, as well as different generation and capture methods, rendering methods, data caching algorithms and output displays. The API will also support hybrid light-field and geometry based models, as well as light-field resampling and composition.

This paper presents a novel approach to capture light field in camera arrays based on the tensor recovery framework. Light fields are acquired by a linear array of cameras with overlapping field of view. We represent the light fields in shape of a tensor to exploit both local and non-local correlated structures of cameras image. The methodology is inspired by the recent research on matrix completion. We extend the affine matrix rank minimization to low-rank tensor recovery for light field acquisition, using a convex relaxation technique of the matrix rank. Finally, we develop a quantitative evaluation on a synthetic scene to assess our method with low-n-rank tensor recovery algorithm to assure the accuracy of our scheme with far less computational cost.

International audience; This paper describes a novel light field compression scheme using a depth image-based view synthesis technique. A small subset of views is compressed with HEVC inter coding and then used to reconstruct the entire light field. The residual of the whole light field can be then restructured as a video sequence and encoded by HEVC inter coding. Experiments show that our scheme significantly outperforms a similar view synthesis method which utilizes convolutional neural networks, and does not require training with a large dataset of light fields as required by deep learning techniques. It also outperforms as well the direct encoding of all the light field views.

Date of Conference: 12-15 April 2015 Conference Name: Optical Trapping Applications, OTA 2015 Speckles are random light fields that share some universal statistical properties. Because of this, they can be used to perform deterministic optical manipulation tasks on a Brownian particle as well as control its diffusion properties.

This paper presents a novel approach to capture light field in cam- era arrays based on the compressive sensing framework.

We present a novel approach to the reconstruction of depth from light field data. Our method uses dictionary representations and group sparsity constraints to derive a convex formulation. Although our solution results in an increase of the problem dimensionality, we keep numerical complexity at bay by restricting the space of solutions and by exploiting an efficient Primal-Dual formulation. Comparisons with state of the art techniques, on both synthetic and real data, show promising performances.

This paper presents a novel approach to capture light field in camera arrays based on the compressive sensing framework. Light fields are captured by a linear array of cameras with overlapping field of view. In this work, we design a redundant dictionary to exploit cross-cameras correlated structures in order to sparsely represent cameras image. We show experimentally that the projection of complex synthetic scenes into the designed dictionary yield very sparse coefficients.