Publications by authors named "Jeppe Revall Frisvad"

7 Publications

  • Page 1 of 1

Surface Reconstruction from Structured Light Images Using Differentiable Rendering.

Sensors (Basel) 2021 Feb 4;21(4). Epub 2021 Feb 4.

DTU Compute, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.

When 3D scanning objects, the objective is usually to obtain a continuous surface. However, most surface scanning methods, such as structured light scanning, yield a point cloud. Obtaining a continuous surface from a point cloud requires a subsequent surface reconstruction step, which is directly affected by any error from the computation of the point cloud. In this work, we propose a one-step approach in which we compute the surface directly from structured light images. Our method minimizes the least-squares error between photographs and renderings of a triangle mesh, where the vertex positions of the mesh are the parameters of the minimization problem. To ensure fast iterations during optimization, we use differentiable rendering, which computes images and gradients in a single pass. We present simulation experiments demonstrating that our method for computing a triangle mesh has several advantages over approaches that rely on an intermediate point cloud. Our method can produce accurate reconstructions when initializing the optimization from a sphere. We also show that our method is good at reconstructing sharp edges and that it is robust with respect to image noise. In addition, our method can improve the output from other reconstruction algorithms if we use these for initialization.
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http://dx.doi.org/10.3390/s21041068DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7913955PMC
February 2021

Alignment of rendered images with photographs for testing appearance models.

Appl Opt 2020 Nov;59(31):9786-9798

We propose a method for direct comparison of rendered images with a corresponding photograph in order to analyze the optical properties of physical objects and test the appropriateness of appearance models. To this end, we provide a practical method for aligning a known object and a point-like light source with the configuration observed in a photograph. Our method is based on projective transformation of object edges and silhouette matching in the image plane. To improve the similarity between rendered and photographed objects, we introduce models for spatially varying roughness and a model where the distribution of light transmitted by a rough surface influences direction-dependent subsurface scattering. Our goal is to support development toward progressive refinement of appearance models through quantitative validation.
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http://dx.doi.org/10.1364/AO.398055DOI Listing
November 2020

Phase function of a spherical particle when scattering an inhomogeneous electromagnetic plane wave.

J Opt Soc Am A Opt Image Sci Vis 2018 Apr;35(4):669-680

In absorbing media, electromagnetic plane waves are most often inhomogeneous. Existing solutions for the scattering of an inhomogeneous plane wave by a spherical particle provide no explicit expressions for the scattering components. In addition, current analytical solutions require evaluation of the complex hypergeometric function F2 for every term of a series expansion. In this work, I develop a simpler solution based on associated Legendre functions with argument zero. It is similar to the solution for homogeneous plane waves but with new explicit expressions for the angular dependency of the far-field scattering components, that is, the phase function. I include recurrence formulas for practical evaluation and provide numerical examples to evaluate how well the new expressions match previous work in some limiting cases. The predicted difference in the scattering phase function due to inhomogeneity is not negligible for light entering an absorbing medium at an oblique angle. The presented theory could thus be useful for predicting scattering behavior in dye-based random lasing and in solar cell absorption enhancement.
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http://dx.doi.org/10.1364/JOSAA.35.000669DOI Listing
April 2018

Scene reassembly after multimodal digitization and pipeline evaluation using photorealistic rendering.

Appl Opt 2017 Sep;56(27):7679-7690

Transparent objects require acquisition modalities that are very different from the ones used for objects with more diffuse reflectance properties. Digitizing a scene where objects must be acquired with different modalities requires scene reassembly after reconstruction of the object surfaces. This reassembly of a scene that was picked apart for scanning seems unexplored. We contribute with a multimodal digitization pipeline for scenes that require this step of reassembly. Our pipeline includes measurement of bidirectional reflectance distribution functions and high dynamic range imaging of the lighting environment. This enables pixelwise comparison of photographs of the real scene with renderings of the digital version of the scene. Such quantitative evaluation is useful for verifying acquired material appearance and reconstructed surface geometry, which is an important aspect of digital content creation. It is also useful for identifying and improving issues in the different steps of the pipeline. In this work, we use it to improve reconstruction, apply analysis by synthesis to estimate optical properties, and to develop our method for scene reassembly.
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http://dx.doi.org/10.1364/AO.56.007679DOI Listing
September 2017

Noninvasive particle sizing using camera-based diffuse reflectance spectroscopy.

Appl Opt 2016 May;55(14):3840-6

Diffuse reflectance measurements are useful for noninvasive inspection of optical properties such as reduced scattering and absorption coefficients. Spectroscopic analysis of these optical properties can be used for particle sizing. Systems based on optical fiber probes are commonly employed, but their low spatial resolution limits their validity ranges for the coefficients. To cover a wider range of coefficients, we use camera-based spectroscopic oblique incidence reflectometry. We develop a noninvasive technique for acquisition of apparent particle size distributions based on this approach. Our technique is validated using stable oil-in-water emulsions with a wide range of known particle size distributions. We also measure the apparent particle size distributions of complex dairy products. These results show that our tool, in contrast to those based on fiber probes, can deal with a range of optical properties wide enough to track apparent particle size distributions in a typical industrial process.
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http://dx.doi.org/10.1364/AO.55.003840DOI Listing
May 2016

Importance sampling the Rayleigh phase function.

J Opt Soc Am A Opt Image Sci Vis 2011 Dec;28(12):2436-41

Department of Informatics and Mathematical Modelling, Technical University of Denmark, Kgs. Lyngby, Denmark.

Rayleigh scattering is used frequently in Monte Carlo simulation of multiple scattering. The Rayleigh phase function is quite simple, and one might expect that it should be simple to importance sample it efficiently. However, there seems to be no one good way of sampling it in the literature. This paper provides the details of several different techniques for importance sampling the Rayleigh phase function, and it includes a comparison of their performance as well as hints toward efficient implementation.
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http://dx.doi.org/10.1364/JOSAA.28.002436DOI Listing
December 2011

Empirical formula for the refractive index of freezing brine.

Appl Opt 2009 Apr;48(11):2149-53

Department of Informatics and Mathematical Modelling, Technical University of Denmark, Richard Petersens Plads, DTU-Building 321, DK-2800 Lyngby, Denmark.

The refractive index of freezing brine is important in order to, for example, estimate oceanic scattering as sea ice develops. Previously, no simple continuous expression was available for estimating the refractive index of brine at subzero temperatures. I show that extrapolation of the empirical formula for the refractive index of seawater by Quan and Fry [Appl. Opt.34, 3477 (1995)APOPAI0003-693510.1364/AO.34.003477] provides a good fit to the refractive index of freezing brine for temperatures above -24 degrees C and salinities below 180 per thousand.
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http://dx.doi.org/10.1364/ao.48.002149DOI Listing
April 2009
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