The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Steven L Jacques - One of the best experts on this subject based on the ideXlab platform.

  • coupling 3d monte carlo Light Transport in optically heterogeneous tissues to photoacoustic signal generation
    Photoacoustics, 2014
    Co-Authors: Steven L Jacques
    Abstract:

    The generation of photoacoustic signals for imaging objects embedded within tissues is dependent on how well Light can penetrate to and deposit energy within an optically absorbing object, such as a blood vessel. This report couples a 3D Monte Carlo simulation of Light Transport to stress wave generation to predict the acoustic signals received by a detector at the tissue surface. The Monte Carlo simulation allows modeling of optically heterogeneous tissues, and a simple MATLAB™ acoustic algorithm predicts signals reaching a surface detector. An example simulation considers a skin with a pigmented epidermis, a dermis with a background blood perfusion, and a 500-μm-dia. blood vessel centered at a 1-mm depth in the skin. The simulation yields acoustic signals received by a surface detector, which are generated by a pulsed 532-nm laser exposure before and after inserting the blood vessel. A MATLAB™ version of the acoustic algorithm and a link to the 3D Monte Carlo website are provided.

  • tutorial on diffuse Light Transport
    Journal of Biomedical Optics, 2008
    Co-Authors: Steven L Jacques, Brian W. Pogue
    Abstract:

    A tutorial introduction to diffuse Light Transport is presented. The basic analytic equations of time-resolved, steady-state and modu- lated Light Transport are introduced. The perturbation method for han- dling sLight heterogeneities in optical properties is outlined. The treat- ment of boundary conditions such as an air/tissue surface is described. Finite mesh-based numerical methods are introduced to calculate the diffuse Light field in complex tissues with arbitrary boundaries. Appli- cations in tissue spectroscopy and imaging illustrate these theoretical and computational tools. © 2008 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2967535 This report is a tutorial introduction to diffuse Light Transport in biological tissues. Section 1 presents the basics of diffuse Light Transport, showing the simple equations for time- resolved, steady-state, and modulated Light Transport. The per- turbation method for handling sLight heterogeneities in optical properties is introduced. The treatment of an air/tissue surface boundary condition is considered. Section 2 describes numeri- cal methods for simulating Light Transport in complex tissues. The goal of this work is to provide the novice in biomedical optics with an introduction to diffuse Light Transport, and the underpinnings of how basic approaches to solving Light trans- port problems can be solved.

  • three monte carlo programs of polarized Light Transport into scattering media part i
    Optics Express, 2005
    Co-Authors: Jessica C Ramellaroman, Scott A Prahl, Steven L Jacques
    Abstract:

    Propagation of Light into scattering media is a complex problem that can be modeled using statistical methods such as Monte Carlo. Few Monte Carlo programs have so far included the information regarding the status of polarization of Light before and after a scattering event. Different approaches have been followed and limited numerical values have been made available to the general public. In this paper, three different ways to build a Monte Carlo program for Light propagation with polarization are given. Different groups have used the first two methods; the third method is original. Comparison in between Monte Carlo runs and Adding Doubling program yielded less than 1 % error.

  • three monte carlo programs of polarized Light Transport into scattering media part ii
    Optics Express, 2005
    Co-Authors: Jessica C Ramellaroman, Scott A Prahl, Steven L Jacques
    Abstract:

    Three Monte Carlo programs were developed which keep track of the status of polarization of Light traveling through mono-disperse solutions of micro-spheres. These programs were described in detail in our previous article [1]. This paper illustrates a series of Monte Carlo simulations that model common experiments of Light transmission and reflection of scattering media. Furthermore the codes were expanded to model Light propagating through poly-disperse solutions of micro-spheres of different radii distributions.

  • mcml monte carlo modeling of Light Transport in multi layered tissues
    Computer Methods and Programs in Biomedicine, 1995
    Co-Authors: Lihong V Wang, Steven L Jacques, Liqiong Zheng
    Abstract:

    A Monte Carlo model of steady-state Light Transport in multi-layered tissues (MCML) has been coded in ANSI Standard C; therefore, the program can be used on various computers. Dynamic data allocation is used for MCML, hence the number of tissue layers and grid elements of the grid system can be varied by users at run time. The coordinates of the simulated data for each grid element in the radial and angular directions are optimized. Some of the MCML computational results have been verified with those of other theories or other investigators. The program, including the source code, has been in the public domain since 1992.

Ramesh Raskar - One of the best experts on this subject based on the ideXlab platform.

  • relativistic effects for time resolved Light Transport
    Computer Graphics Forum, 2015
    Co-Authors: Adrian Jarabo, Andreas Velten, Belen Masia, Ramesh Raskar, Christopher Barsi, Diego Gutierrez
    Abstract:

    We present a real-time framework which allows interactive visualization of relativistic effects for time-resolved Light Transport. We leverage data from two different sources: real-world data acquired with an effective exposure time of less than 2 picoseconds, using an ultra-fast imaging technique termed femto-photography, and a transient renderer based on ray-tracing. We explore the effects of time dilation, Light aberration, frequency shift and radiance accumulation by modifying existing models of these relativistic effects to take into account the time-resolved nature of Light propagation. Unlike previous works, we do not impose limiting constraints in the visualization, allowing the virtual camera to explore freely a reconstructed 3D scene depicting dynamic illumination. Moreover, we consider not only linear motion, but also acceleration and rotation of the camera. We further introduce, for the first time, a pinhole camera model into our relativistic rendering framework, and account for subsequent changes in focal length and field of view as the camera moves through the scene.

  • a Light Transport model for mitigating multipath interference in time of fLight sensors
    Computer Vision and Pattern Recognition, 2015
    Co-Authors: Nikhil Naik, Ramesh Raskar, Christoph Rhemann, Achuta Kadambi, Shahram Izadi, Sing Bing Kang
    Abstract:

    Continuous-wave Time-of-fLight (TOF) range imaging has become a commercially viable technology with many applications in computer vision and graphics. However, the depth images obtained from TOF cameras contain scene dependent errors due to multipath interference (MPI). Specifically, MPI occurs when multiple optical reflections return to a single spatial location on the imaging sensor. Many prior approaches to rectifying MPI rely on sparsity in optical reflections, which is an extreme simplification. In this paper, we correct MPI by combining the standard measurements from a TOF camera with information from direct and global Light Transport. We report results on both simulated experiments and physical experiments (using the Kinect sensor). Our results, evaluated against ground truth, demonstrate a quantitative improvement in depth accuracy.

  • decomposing global Light Transport using time of fLight imaging
    International Journal of Computer Vision, 2014
    Co-Authors: Andreas Velten, Matthew Otoole, Belen Masia, Amit Agrawal, Qionghai Dai, Ramesh Raskar
    Abstract:

    Global Light Transport is composed of direct and indirect components. In this paper, we take the first steps toward analyzing Light Transport using the high temporal resolution information of time of fLight (ToF) images. With pulsed scene illumination, the time profile at each pixel of these images separates different illumination components by their finite travel time and encodes complex interactions between the incident Light and the scene geometry with spatially-varying material properties. We exploit the time profile to decompose Light Transport into its constituent direct, subsurface scattering, and interreflection components. We show that the time profile is well modelled using a Gaussian function for the direct and interreflection components, and a decaying exponential function for the subsurface scattering component. We use our direct, subsurface scattering, and interreflection separation algorithm for five computer vision applications: recovering projective depth maps, identifying subsurface scattering objects, measuring parameters of analytical subsurface scattering models, performing edge detection using ToF images and rendering novel images of the captured scene with adjusted amounts of subsurface scattering.

  • ultra fast lensless computational imaging through 5d frequency analysis of time resolved Light Transport
    Springer US, 2013
    Co-Authors: Gordon Wetzstein, Qionghai Dai, Christopher Barsi, Thomas Willwacher, Ramesh Raskar
    Abstract:

    Light Transport has been analyzed extensively, in both the primal domain and the frequency domain. Frequency analyses often provide intuition regarding effects introduced by Light propagation and interaction with optical elements; such analyses encourage optimal designs of computational cameras that efficiently capture tailored visual information. However, previous analyses have relied on instantaneous propagation of Light, so that the measurement of the time dynamics of Light---scene interaction, and any resulting information transfer, is precluded. In this paper, we relax the common assumption that the speed of Light is infinite. We analyze free space Light propagation in the frequency domain considering spatial, temporal, and angular Light variation. Using this analysis, we derive analytic expressions for information transfer between these dimensions and show how this transfer can be exploited for designing a new lensless imaging system. With our frequency analysis, we also derive performance bounds for the proposed computational camera architecture and provide a mathematical framework that will also be useful for future ultra-fast computational imaging systems.

  • primal dual coding to probe Light Transport
    International Conference on Computer Graphics and Interactive Techniques, 2012
    Co-Authors: Matthew Otoole, Ramesh Raskar, Kiriakos N. Kutulakos
    Abstract:

    We present primal-dual coding, a photography technique that enables direct fine-grain control over which Light paths contribute to a photo. We achieve this by projecting a sequence of patterns onto the scene while the sensor is exposed to Light. At the same time, a second sequence of patterns, derived from the first and applied in lockstep, modulates the Light received at individual sensor pixels. We show that photography in this regime is equivalent to a matrix probing operation in which the elements of the scene's Transport matrix are individually re-scaled and then mapped to the photo. This makes it possible to directly acquire photos in which specific Light Transport paths have been blocked, attenuated or enhanced. We show captured photos for several scenes with challenging Light Transport effects, including specular inter-reflections, caustics, diffuse inter-reflections and volumetric scattering. A key feature of primal-dual coding is that it operates almost exclusively in the optical domain: our results consist of directly-acquired, unprocessed RAW photos or differences between them.

Kiriakos N. Kutulakos - One of the best experts on this subject based on the ideXlab platform.

  • 3d shape and indirect appearance by structured Light Transport
    IEEE Transactions on Pattern Analysis and Machine Intelligence, 2016
    Co-Authors: Matthew Otoole, John Mather, Kiriakos N. Kutulakos
    Abstract:

    We consider the problem of deliberately manipulating the direct and indirect Light flowing through a time-varying, general scene in order to simplify its visual analysis. Our approach rests on a crucial link between stereo geometry and Light Transport: while direct Light always obeys the epipolar geometry of a projector-camera pair, indirect Light overwhelmingly does not. We show that it is possible to turn this observation into an imaging method that analyzes Light Transport in real time in the optical domain, prior to acquisition. This yields three key abilities that we demonstrate in an experimental camera prototype: (1) producing a live indirect-only video stream for any scene, regardless of geometric or photometric complexity; (2) capturing images that make existing structured-Light shape recovery algorithms robust to indirect Transport; and (3) turning them into one-shot methods for dynamic 3D shape capture.

  • temporal frequency probing for 5d transient analysis of global Light Transport
    International Conference on Computer Graphics and Interactive Techniques, 2014
    Co-Authors: Matthew Otoole, Matthias B. Hullin, Felix Heide, Wolfgang Heidrich, Lei Xiao, Kiriakos N. Kutulakos
    Abstract:

    We analyze Light propagation in an unknown scene using projectors and cameras that operate at transient timescales. In this new photography regime, the projector emits a spatio-temporal 3D signal and the camera receives a transformed version of it, determined by the set of all Light Transport paths through the scene and the time delays they induce. The underlying 3D-to-3D transformation encodes scene geometry and global Transport in great detail, but individual Transport components (e.g., direct reflections, inter-reflections, caustics, etc.) are coupled nontrivially in both space and time. To overcome this complexity, we observe that transient Light Transport is always separable in the temporal frequency domain. This makes it possible to analyze transient Transport one temporal frequency at a time by trivially adapting techniques from conventional projector-to-camera Transport. We use this idea in a prototype that offers three never-seen-before abilities: (1) acquiring time-of-fLight depth images that are robust to general indirect Transport, such as interreflections and caustics; (2) distinguishing between direct views of objects and their mirror reflection; and (3) using a photonic mixer device to capture sharp, evolving wavefronts of "Light-in-fLight".

  • primal dual coding to probe Light Transport
    International Conference on Computer Graphics and Interactive Techniques, 2012
    Co-Authors: Matthew Otoole, Ramesh Raskar, Kiriakos N. Kutulakos
    Abstract:

    We present primal-dual coding, a photography technique that enables direct fine-grain control over which Light paths contribute to a photo. We achieve this by projecting a sequence of patterns onto the scene while the sensor is exposed to Light. At the same time, a second sequence of patterns, derived from the first and applied in lockstep, modulates the Light received at individual sensor pixels. We show that photography in this regime is equivalent to a matrix probing operation in which the elements of the scene's Transport matrix are individually re-scaled and then mapped to the photo. This makes it possible to directly acquire photos in which specific Light Transport paths have been blocked, attenuated or enhanced. We show captured photos for several scenes with challenging Light Transport effects, including specular inter-reflections, caustics, diffuse inter-reflections and volumetric scattering. A key feature of primal-dual coding is that it operates almost exclusively in the optical domain: our results consist of directly-acquired, unprocessed RAW photos or differences between them.

  • reconstructing the surface of inhomogeneous transparent scenes by scatter trace photography
    International Conference on Computer Vision, 2007
    Co-Authors: N J W Morris, Kiriakos N. Kutulakos
    Abstract:

    We present a new method for reconstructing the exterior surface of a complex transparent scene with inhomogeneous interior (e.g., multiple interfaces, reflective or painted interiors, etc). Our approach involves capturing images of the scene from one or more viewpoints while moving a proximal Light source to a 2D or 3D set of positions. This gives a 2D (or 3D) dataset per pixel, called the scatter trace. The key idea of our approach is that even though Light Transport within a transparent scene's interior can be exceedingly complex, the scatter trace of each pixel has a highly-constrained geometry that (1) reveals the contribution of direct surface reflection, and (2) leads to a simple "scatter- trace stereo" algorithm for computing the local geometry of the exterior surface (depth and surface normals). We present 3D reconstruction results for a variety of scenes that exhibit complex Light Transport phenomena.

  • a theory of inverse Light Transport
    International Conference on Computer Vision, 2005
    Co-Authors: Steven M Seitz, Yasuyuki Matsushita, Kiriakos N. Kutulakos
    Abstract:

    In this paper we consider the problem of computing and removing interreflections in photographs of real scenes. Towards this end, we introduce the problem of inverse Light Transport - given a photograph of an unknown scene, decompose it into a sum of n-bounce images, where each image records the contribution of Light that bounces exactly n times before reaching the camera. We prove the existence of a set of interreflection cancelation operators that enable computing each n-bounce image by multiplying the photograph by a matrix. This matrix is derived from a set of "impulse images" obtained by probing the scene with a narrow beam of Light. The operators work under unknown and arbitrary illumination, and exist for scenes that have arbitrary spatially-varying BRDFs. We derive a closed-form expression for these operators in the Lambertian case and present experiments with textured and untextured Lambertian scenes that confirm our theory's predictions

Alexander D Klose - One of the best experts on this subject based on the ideXlab platform.

  • Light Transport in biological tissue using three dimensional frequency domain simplified spherical harmonics equations
    Physics in Medicine and Biology, 2009
    Co-Authors: Michael Chu, Alexander D Klose, Karthik Vishwanath, Hamid Dehghani
    Abstract:

    The accuracy of the commonly used diffusion approximation as used in diffuse optical tomography is known to be limited in cases involving strong absorption and in these situations a higher ordered approximation is necessary. In this study, a Light Transport model has been developed based upon the three-dimensional frequency-domain simplified spherical harmonics (SPN) approximation for orders up to N = 7. The SPN data are tested against a semi-infinite multi-layered Monte Carlo model. It has been shown that the SPN approximation for higher orders (N >1) provides an increase in accuracy over the diffusion equation specifically near sources and at boundaries of regions with increased optical absorption. It is demonstrated that the error of fluence calculated near the sources between the diffusion approximation and the SPN model (N = 7) can be as large as 60%, therefore limiting the use of the diffusion approximation for small animal imaging and in situations where optical changes near sources are critical for tomographic reconstructions. (Some figures in this article are in colour only in the electronic version)

  • Light Transport in biological tissue based on the simplified spherical harmonics equations
    Journal of Computational Physics, 2006
    Co-Authors: Alexander D Klose, Edward W Larsen
    Abstract:

    In this work, we demonstrate the validity of the simplified spherical harmonics equations to approximate the more complicated equation of radiative transfer for modeling Light propagation in biological tissue. We derive the simplified spherical harmonics equations up to order N=7 for anisotropic scattering and partially reflective boundary conditions. We compare numerical results with diffusion and discrete ordinates Transport solutions. We find that the simplified spherical harmonics methods significantly improve the diffusion solution in Transport-like domains with high absorption and small geometries, and are computationally less expensive than the discrete ordinates Transport method. For example, the simplified P"3 method is approximately two orders of magnitude faster than the discrete ordinates Transport method, but only 2.5 times computationally more demanding than the diffusion method. We conclude that the simplified spherical harmonics methods can accurately model Light propagation in small tissue geometries at visible and near-infrared wavelengths, yielding Transport-like solutions with only a fraction of the computational cost of the Transport calculation.

Gordon Wetzstein - One of the best experts on this subject based on the ideXlab platform.

  • non line of sight imaging with partial occluders and surface normals
    ACM Transactions on Graphics, 2019
    Co-Authors: Felix Heide, Matthew Otoole, Kai Zang, David B Lindell, Steven Diamond, Gordon Wetzstein
    Abstract:

    Imaging objects obscured by occluders is a significant challenge for many applications. A camera that could “see around corners” could help improve navigation and mapping capabilities of autonomous vehicles or make search and rescue missions more effective. Time-resolved single-photon imaging systems have recently been demonstrated to record optical information of a scene that can lead to an estimation of the shape and reflectance of objects hidden from the line of sight of a camera. However, existing non-line-of-sight (NLOS) reconstruction algorithms have been constrained in the types of Light Transport effects they model for the hidden scene parts. We introduce a factored NLOS Light Transport representation that accounts for partial occlusions and surface normals. Based on this model, we develop a factorization approach for inverse time-resolved Light Transport and demonstrate high-fidelity NLOS reconstructions for challenging scenes both in simulation and with an experimental NLOS imaging system.

  • ultra fast lensless computational imaging through 5d frequency analysis of time resolved Light Transport
    Springer US, 2013
    Co-Authors: Gordon Wetzstein, Qionghai Dai, Christopher Barsi, Thomas Willwacher, Ramesh Raskar
    Abstract:

    Light Transport has been analyzed extensively, in both the primal domain and the frequency domain. Frequency analyses often provide intuition regarding effects introduced by Light propagation and interaction with optical elements; such analyses encourage optimal designs of computational cameras that efficiently capture tailored visual information. However, previous analyses have relied on instantaneous propagation of Light, so that the measurement of the time dynamics of Light---scene interaction, and any resulting information transfer, is precluded. In this paper, we relax the common assumption that the speed of Light is infinite. We analyze free space Light propagation in the frequency domain considering spatial, temporal, and angular Light variation. Using this analysis, we derive analytic expressions for information transfer between these dimensions and show how this transfer can be exploited for designing a new lensless imaging system. With our frequency analysis, we also derive performance bounds for the proposed computational camera architecture and provide a mathematical framework that will also be useful for future ultra-fast computational imaging systems.

  • radiometric compensation through inverse Light Transport
    Pacific Conference on Computer Graphics and Applications, 2007
    Co-Authors: Gordon Wetzstein, Oliver Bimber
    Abstract:

    Radiometric compensation techniques allow seamless projections onto complex everyday surfaces. Implemented with projector-camera systems they support the presentation of visual content in situations where projection-optimized screens are not available or not desired - as in museums, historic sites, air-plane cabins, or stage performances. We propose a novel approach that employs the full Light Transport between projectors and a camera to account for many illumination aspects, such as interreflections, refractions, shadows, and defocus. Precomputing the inverse Light Transport in combination with an efficient implementation on the GPU makes the real-time compensation of captured local and global Light modulations possible.