Movie projector | EPFL Graph Search

A movie projector is an opto-mechanical device for displaying motion picture film by projecting it onto a screen. Most of the optical and mechanical elements, except for the illumination and sound devices, are present in movie cameras. Modern movie projectors are specially built video projectors (see also digital cinema). Many projectors are specific to a particular film gauge and not all movie projectors are film projectors since the use of film is required. Predecessors The main precursor to the movie projector was the magic lantern. In its most common setup it had a concave mirror behind a light source to help direct as much light as possible through a painted glass picture slide and a lens, out of the lantern onto a screen. Simple mechanics to have the painted images moving were probably implemented since Christiaan Huygens introduced the apparatus around 1659. Initially candles and oil lamps were used, but other light sources, such as the argand lamp and limelight

Precise and accurate image-based measurements of optical material properties

Marjan Shahpaski

The appearance of objects is governed by how they reflect, transmit and absorb the light they receive. That, in turn, depends on the material's internal structure, surface structure, and viewing and illumination directions. Changes in those characteristics can produce dramatic shifts in a material's appearance. In this thesis, we explore how the optical properties can be estimated accurately using computational imaging. Current solutions are based on using instruments that are on the expensive side, such as spectrophotometers, profilometers and goniophotometers; hence, we explore the use of more affordable equipment, such as cameras. We start with the reflected light, and how the surface structure and roughness can be measured with commodity hardware such as projectors and cameras. We continue to the transmitted light, where we study methods for measuring hemispherical and directional transmittance. Systems based on the projection of structured light can be used for high-precision depth estimation. These methods provide non-contact means of depth estimation by using a calibrated camera-projector pair. Calibration of such systems is a cumbersome and time-consuming task. We, thus, present a novel method that allows for simultaneous geometric and radiometric calibration of a projector-camera pair. We leverage the different colorimetric properties of the printed and projected patterns to perform the geometric calibration, and perform the radiometric calibration of the projector with the information contained inside the projected squares. We show that our method performs on par with current approaches that all require separate geometric and radiometric calibration. We then apply the algorithm to calibrate a structured light system with the goal of surface structure estimation of nearly planar surfaces. The surface structure is then used to calculate their macroscopic surface roughness. Over a set of samples, our results are comparable to those from a high-grade commercial profilometer. The accurate measurement of transmittance properties of materials is essential in the printing and display industries to ensure accurate color reproduction. We explore different measurement geometries for total transmittance, and show that the measurements are highly affected by the geometry used, since certain geometries can introduce a measurement bias. We build a flexible custom setup that can simulate these geometries, and evaluate it qualitatively and quantitatively. We also compare its measurements to those of widely used commercial solutions, and show that significant differences exist over our test set. These findings stress the importance of including the measurement geometry when reporting total transmittance. The BSDF is of great importance in many applications, from rendering and visual special effects to architectural modelling of illumination. We propose a novel design for the measurement of BSDF, more specifically the BTDF. It is based on radial catadioptric imaging, where we illuminate the measured sample with a collimated beam of light, the emerging light on the other side of the sample is collected by a diffusing cylinder, and a camera registers the steady-state radiance. After inverting the light transport inside the cylinder, we can compute the sample's BTDF. In simulations, our proposed design achieves results that are well aligned with the ground truth, for both smooth and high-frequency BTDFs that feature sharp intensity changes.

EPFL2020

An improved model for the accurate calculation of parallel heat fluxes at the JET bulk tungsten outer divertor

Otto Asunta, Patrick Blanchard, Yann Camenen, Stefano Coda, Basil Duval, Ambrogio Fasoli, Jonathan Marc Philippe Faustin, Davide Galassi, Javier García Hernández, Jonathan Graves, Jan Horacek, Samuel Lanthaler, Yves Martin, Mikhail Maslov, Federico Nespoli, Hamish William Patten, Alessandro Pau, Antonio José Pereira de Figueiredo, David Pfefferlé, Richard Pitts, Olivier Sauter, Cristian Sommariva, Duccio Testa, Nicola Vianello, Henri Weisen, Dalziel Joseph Wilson, Marco Wischmeier, Liang Yao, Yao Zhou

Parallel heat flux calculations at the JET divertor have been based on the assumption that all incoming heat is due to the projection of the heat flux parallel to the magnetic line, q, plus a constant background. This simplification led to inconsistencies during the analysis of a series of dedicated tungsten melting experiments performed in 2013, for which infrared (IR) thermography surface measurements could not be recreated through simulations unless the parallel heat flux was reduced by 80% for L-mode and 60% for H-mode. We give an explanation for these differences using a new IR inverse analysis code, a set of geometrical corrections, and most importantly an additional term for the divertor heat flux accounting for non-parallel effects such as cross-field transport, recycled neutrals or charge exchange. This component has been evaluated comparing four different geometries with impinging angles varying from 2 to 90 degrees. Its magnitude corresponds to 1.2%-1.9% of q(parallel to), but because it is not affected by the magnetic projection, it accounts for up to 20%-30% of the tile surface heat flux. The geometrical corrections imply a further reduction of 24% of the measured heat flux. In addition, the application of the new inverse code increases the accuracy of the tile heat flux calculation, eliminating any previous discrepancy. The parallel heat flux computed with this new model is actually much lower than previously deduced by inverse analysis of IR temperatures-40% for L-mode and 50% for H-mode-while being independent of the geometry on which it is measured. This main result confirms the validity of the optical projection as long as a non-constant and non-parallel component is considered. For a given total heating power, the model predicts over 10% reduction of the maximum tile surface heat flux compared to strict optical modelling, as well as a 30% reduced sensitivity to manufacturing and assembling tolerances. These conclusions, along with the improvement in the predictability of the divertor thermal behaviour, are critical for JET future DT operations, and are also directly applicable to the design of the ITER divertor monoblocks.

2018

NMR Crystallography of Campho[2,3-c]pyrazole (Z `=6): Combining High-Resolution H-1-C-13 Solid-State MAS NMR Spectroscopy and GIPAW Chemical-Shift Calculations

David Lyndon Emsley

H-1-C-13 two-dimensional magic-angle spinning (MAS) solid-state NMR correlation spectra, recorded with the MAS-J-HMQC experiment, are presented for campho[2,3-c]pyrazole. For each C-13 moiety, there are six resonances associated with the six distinct molecules in the asymmetric unit cell (Z' = 6). The one-bond C-H correlations observed in the 2D H-1-C-13 MAS-J-HMQC spectra allow the experimental determination of the H-1 and C-13 chemical shifts associated with the separate CH, CH2, and CH3 groups. H-1 and C-13 chemical shifts calculated by using the GIPAW (Gauge Including Projector Augmented Waves) plane-wave pseudopotential approach are presented. Calculations for the whole unit cell (12 x 29 = 348 atoms, with geometry optimization of all atoms) allow the assignment of the experimental H-1 and C-13 chemical shifts to the six distinct molecules, The calculated chemical shifts for the full crystal structure are compared with those for isolated molecules as extracted from the geometry-optimized crystal structure. In this way, the effect of intermolecular interactions on the observed chemical shifts is quantified. In particular, the calculations are sufficiently precise to differentiate the small (

AMER CHEMICAL SOC2010

Precise and accurate image-based measurements of optical material properties

Marjan Shahpaski

EPFL2020

An improved model for the accurate calculation of parallel heat fluxes at the JET bulk tungsten outer divertor

2018