Ray Distortion Research Articles

Correcting ray distortion in tomographic additive manufacturing.

Light-based additive manufacturing techniques enable a rapid transition from object design to production. In these approaches, a 3D object is typically built by successive polymerization of 2D layers in a photocurable resin. A recently demonstrated technique, however, uses tomographic dose patterning to establish a 3D light dose distribution within a cylindrical glass vial of photoresin. Lensing distortion from the cylindrical vial is currently mitigated by either an index matching bath around the print volume or a cylindrical lens. In this work, we show that these hardware approaches to distortion correction are unnecessary. Instead, we demonstrate how the lensing effect can be computationally corrected by resampling the parallel-beam radon transform into an aberrated geometry. We also demonstrate a more general application of our computational approach by correcting for non-telecentricity inherent in most optical projection systems. We expect that our results will underpin a more simple and flexible class of tomographic 3D printers where deviations from the assumed parallel-beam projection geometry are rectified computationally.

Perspective Camera Model With Refraction Correction for Optical Velocimetry Measurements in Complex Geometries.

Camera calibration is among the most challenging aspects of the investigation of fluid flows around complex transparent geometries, due to the optical distortions caused by the refraction of the lines-of-sight at the solid/fluid interfaces. This work presents a camera model which exploits the pinhole-camera approximation and represents the refraction of the lines-of-sight directly via Snell's law. The model is based on the computation of the optical ray distortion in the 3D scene and dewarping of the object points to be projected. The present procedure is shown to offer a faster convergence rate and greater robustness than other similar methods available in the literature. Issues inherent to estimation of the refractive extrinsic and intrinsic parameters are discussed and feasible calibration approaches are proposed. The effects of image noise, volume size of the control point grid and number of cameras on the calibration procedure are analyzed. Finally, an application of the camera model to the 3D optical velocimetry measurements of thermal convection inside a polymethylmethacrylate (PMMA) cylinder immersed in water is presented. A specific calibration procedure is designed for such a challenging experiment where the cylinder interior is not physically accessible and its effectiveness is demonstrated by providing velocity field reconstructions.

Image distortion correction method in a nonuniform temperature field by using Runge-Kutta ray tracing.

To solve the imaging distortion problem in a nonuniform temperature field for visual measurement, this paper studies the Runge-Kutta ray tracing algorithm. First, the light ray emitted by the spatial light point will be abstracted by the proposed method. Then, the ray trajectory in a 3D nonuniform temperature gradient environment will be reproduced, and the ray distortion can be corrected. Finally, the distortion is compared with the actual image distortion obtained through the corner detection method. The experimental results show that the correction method for the distortion image caused by nonuniform temperature gradient heat source interference is feasible by using the Runge-Kutta ray tracing algorithm, which can realize the error compensation for image distortion and obtain an accurate corrected image.

3D reconstruction under light ray distortion from parametric focal cameras

In this paper, we propose a new method for reconstructing 3D objects under light ray distortion caused by unknown refractive media. The proposed method can reconstruct 3D scene, even if light rays projected into the cameras are refracted by unknown refractive media, such as glasses and raindrops. For this objective, we represent light ray projection of multiple cameras by using a pair of planes shared by the multiple cameras in the scene. By using this model, intrinsic and extrinsic camera parameters as well as the refractive properties of the refractive media can be represented efficiently. By using the newly defined camera model, we propose a method for recovering 3D points and camera parameters with refractive properties simultaneously. The experimental results show the efficiency of the proposed camera model and reconstruction method.

Single‐scattering properties of aggregates of plates

AbstractDuring the 2006 Tropical Warm Pool International Cloud Experiment (TWP‐ICE) sponsored by the Atmospheric Radiation Measurement programme, the Scaled Composites Proteus aircraft executed spiral profiles and flew horizontal legs through aging anvils, fresh anvils, and cirrus of unknown origin in the vicinity of Darwin, Australia. Pristine ice crystals including both plates and bullet rosettes, their aggregates, and unclassifiable ice crystals were observed by a Cloud Particle Imager. The widths of observed plates ranged between 80 µm and 200 µm. When a fresh dissipating anvil was observed on 2 February, aggregates of plates contributed 46.2% of the total area of measured ice crystals with maximum dimensions greater than 200 µm, while it was only 7.2% and 1.0% for 27 and 29 January, respectively, when aged cirrus was sampled. Because aggregates of plates have been observed to make large contributions to projected ice crystal area near convection during TWP‐ICE and other projects, their single‐scattering properties that have not been previously examined are investigated here.The dependence of the scattering phase function P11, asymmetry parameter g, and single‐scattering albedo ω0 on three parameters (the area ratio AR, normalized projected area An, and a newly defined aggregation index AI which varies between 0 and 1 with ice crystals with more compact shape having lower AI) defining the three‐dimensional shapes of aggregates of plates were calculated using a geometric ray‐tracing code at wavelengths λ of 0.55, 1.38 and 2.13 µm. The scattering properties depended on the crystal morphology with, for example, the g of an aggregate of plates with a high AI of 0.818 differing by + 6.89% (+6.44%; + 4.55%) from that with a lower AI of 0.378 at λ of 0.55 µm (1.38 µm; 2.13 µm), but by only + 0.29% (+0.25%; − 0.03%) from those of the component plates. The ω0 at absorbing λ increased with AI, 1 − AR, and An. Adding ray distortion to the aggregates caused a decrease in forward scattering and an increase in lateral and backward scattering, decreasing g, an effect that weakened with λ due to absorption. The aggregates of plates with low AI were more influenced by ray distortion compared to those with high AI. The dependence of scattering properties on crystal morphology noted here should be considered when computing bulk scattering properties of ice clouds to determine its importance for climate and remote‐sensing studies. Copyright © 2009 Royal Meteorological Society

Effects of motion of an imaging system and optical image stabilizer on the modulation transfer function

This paper analyzes the effects due to the angular motion of a small-sized imaging system equipped with an optical image stabilizer (OIS) on image quality. Accurate lens moving distances for the OIS required to compensate the ray distortion induced by the angular motion are determined. To calculate the associated modulation transfer function, the integrated and the compensated point spread functions are defined. Finally, the deterioration of the image resolution due to angular motion and the restorative performance of the OIS are analyzed by isolating seven types of angular motion.

P-149: Improved Dual Paraboloid Reflector System using Non-Spherical Retro-Reflector for Projection Display

The Wavien dual paraboloid reflector system is an imaging reflector system having a 1:1 magnification characteristic that allows focusing the light from the arc into the target light pipe with practically no change in etendue. A retro-reflector is used to increase the brightness by reflecting part of the light back through the arc itself. Due to the ray distortion created by the envelop of the burner, especially for UHP lamps where they are very thick and uneven, the reflected images are aberrated reducing the coupling efficiency. In this paper, a non-spherical retro-reflector is used to correct image distortion, thus increasing the coupling efficiency. A system using a spheroid section retro-reflector had been modeled using ASAP and we have observed a significant improvement in retro performance. Use of simple compensating optics interposed between the lamp and a spherical retro reflector is also discussed.

Le Violon d'Ingres: Man Ray's Variations on Ingres, Deformation, Desire and de Sade

Le Violon d'Ingres is a complex photograph that demonstrates Man Ray's long‐standing admiration for Ingres, as well as his desire to mock tradition. Man Ray's distortion and deformation of the model's body engage Surrealist concepts of metamorphosis and formlessness, but they also belong to a larger context of fascination for Ingres's manipulations of anatomy during the interwar period, as seen in the writings of critics such as André Lhote. The revolutionary nature of Ingres's distortions of the female body had parallels in the social distortions found in the writings of Sade, whom Man Ray and his Surrealist colleagues deeply admired.

Use of the continuity equation for electromagnetic energy flow todescribe radiation transport

In the geometric-optics limit the electromagnetic (EM) continuityequation, which describes EM energy flow, reduces to the radiation transportequation, in which energy flow is described generically as the motion of light(or particle) rays along straight-line trajectories in the direction of a unitvector k̂. In practical applications k̂ is discretized, makingthe transport equation extremely difficult to implement computationally andgiving rise to `ray effect' distortions owing to the non-continuousdistribution of the energy over k̂. In this paper we solve the EMcontinuity equation directly in the transport regime, obtaining an energywhich is continuously distributed in k̂ and free of ray distortion.

Lens-like medium using a diffused composite-elliptic core

The use of composite-elliptic core boundary shapes is proposed for the diffusion formation of lens-like media. This principally can get rid of the mode dispersion or skew ray distortion due to the x <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> y <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> term in the dielectric constant distribution.