Evaluation of CNN-based Single-Image Depth Estimation Methods

While an increasing interest in deep models for single-image depth estimation methods can be observed, established schemes for their evaluation are still limited. We propose a set of novel quality criteria, allowing for a more detailed analysis by focusing on specific characteristics of depth maps. In particular, we address the preservation of edges and planar regions, depth consistency, and absolute distance accuracy. In order to employ these metrics to evaluate and compare state-of-the-art single-image depth estimation approaches, we provide a new high-quality RGB-D dataset. We used a DSLR camera together with a laser scanner to acquire high-resolution images and highly accurate depth maps. Experimental results show the validity of our proposed evaluation protocol

Photonic crystals: enhancing the light output of scintillation based detectors

Zsfassung in dt. SpracheOne of the problems in heavy scintillating materials is related to their high index of refraction. As a consequence, most of the scintillation light produced in the bulk material is trapped inside the crystal due to total internal reflection. These limitations can be overcome by means of Photonic crystals (PhCs). PhCs are nano structured optical materials which can affect the propagation of light in multiple ways. In recent years PhCs contributed to major technological developments in the field of semiconductor lasers, light emitting diodes and photovoltaic applications. In this thesis the capabilities of photonic crystal slabs are investigated with the aim to improve the performance of heavy inorganic scintillators. To study the combination of scintillators and PhCs we used a Monte-Carlo program to simulate the light propagation inside a scintillator and a rigorous coupled wave analysis (RCWA) framework to analyse the optical PhC properties. The simulations show light output improvements of a wide range of scintillating materials due to light scattering effects of the PhC slabs. To prove the simulation results several PhC samples have been produced on top of 1.2 x 2 x 5mm 3 LSO (cerium-doped Lutetium Oxyorthosilicate, Lu2SiO5:Ce3+) scintillators. The nanostructured PhC pattern was made by using electron beam lithography and reactive ion etching (RIE). As a main result, the PhC samples show a 30-60% light output improvement when compared to unstructured reference crystals which is in close accordance with our simulation results.19

Photonic Crystals: Enhancing the Light Output of Scintillation Based Detectors

A scintillator is a material which emits light when excited by ionizing radiation. Such materials are used in a diverse range of applications; From high energy particle physics experiments, X-ray security, to nuclear cameras or positron emission tomography. Future high-energy physics (HEP) experiments as well as next generation medical imaging applications are more and more pushing towards better scintillation characteristics. One of the problems in heavy scintillating materials is related to their high index of refraction. As a consequence, most of the scintillation light produced in the bulk material is trapped inside the crystal due to total internal reflection. The same problem also occurs with light emitting diodes (LEDs) and has for a long time been considered as a limiting factor for their overall efficiency. Recent developments in the area of nanophotonics were showing now that those limitations can be overcome by introducing a photonic crystal (PhC) slab at the outcoupling surface of the substrate. Photonic crystals are optical materials which can affect the propagation of light in multiple ways. In this work, we used 2D PhC slabs consisting of hexagonal placed rods of air or square shaped pillars made of silicon nitride. The 300-500nm thick photonic crystal slab changes the reflection properties of the crystal-air interface in different ways. In our case the pattern was optimized to enable the light extraction of photons which are otherwise confined within the scintillator by total internal reflections. In the simulation part we could show light output improvements of a wide range of scintillating materials due to light scattering effects of the photonic crystal grating. For these calculations we used two different programs. At first, a Monte Carlo program called LITRANI was used to calculate the light propagation inside a common scintillation based detector setup. LITRANI calculates the path of a photon starting from the production inside the crystal by an ionizing event all the way through the different materials until it is absorbed or detected. It uses the Fresnel formulas to calculate the light transition and reflection between different absorbing or non-absorbing materials. The second program in our simulations was used to calculate the light extraction efficiency of our PhC structure. This program calculates the 2D photonic crystal interface using a rigorous coupled wave analysis (RCWA) tool. It was used to determine the reflection and transition parameters of the PhC slab for a photon of a certain angle and polarization. With the combination of these two programs the overall gain of the PhC modified scintillators could be calculated and we could show a theoretical light yield improvement of 60-100% by the use of PhCs. In the practical part of this work it is shown how the first samples of PhC slabs on top of different scintillators were produced. The aim of these demonstrator samples was to confirm the simulation results by measurements. Through the deposition of an auxiliary layer of silicon nitride and the adaptation of the standard electron beam lithography (EBL) parameters we could successfully produce several PhC slabs on top of $1.2 imes 2.6 imes 5mm^3$ lutetium oxyorthosilicate (LSO) scintillators. In the characterization process, the PhC samples showed a 30-60% light yield improvement when compared to an unstructured reference scintillator. In our analysis it could be shown that the measured PhC sample properties are in close accordance with the calculations from our simulations

Tanks and Temples: Benchmarking Large-Scale Scene Reconstruction

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Evaluation of CNN-based Single-Image Depth Estimation Methods

While an increasing interest in deep models for single-image depth estimation (SIDE) can be observed, established schemes for their evaluation are still limited. We propose a set of novel quality criteria, allowing for a more detailed analysis by focusing on specific characteristics of depth maps. In particular, we address the preservation of edges and planar regions, depth consistency, and absolute distance accuracy. In order to employ these metrics to evaluate and compare state-of-the-art SIDE approaches, we provide a new high-quality RGB-D dataset. We used a digital single-lens reflex (DSLR) camera together with a laser scanner to acquire high-resolution images and highly accurate depth maps. Experimental results show the validity of our proposed evaluation protocol

Light Extraction From Scintillating Crystals Enhanced by Photonic Crystal Structures Patterned by Focused Ion Beam

“Photonic Crystals (PhC)” have been used in a variety of fields as a structure for improving the light extraction efficiency from materials with high index of refraction. In previous work we already showed the light extraction improvement of several PhC covered LYSO crystals in computer simulations and practical measurements. In this work, new samples are made using different materials and techniques which allows further efficiency improvements. For rapid prototyping of PhC patterns on scintillators we tested a new method using “Focused Ion Beam (FIB)” patterning. The FIB machine is a device similar to a “Scanning Electron Microscope (SEM)”, but it uses ions (mainly gallium) instead of electrons for the imaging of the samples' surface. The additional feature of FIB devices is the option of surface patterning in nano-scale which was exploited for our samples. Three samples using FIB patterning have been produced. One of them is a direct patterning of the extraction face of a 0.8×0.8×10 $mm^3$ LYSO crystal. The second and third were $TiO_2$ coated LYSO crystal with a 1.4×1.4 $mm^2$ out coupling face partly covered with high-quality photonic crystals. $TiO_2$ has high refractive index (around 2.1 - 2.4)-which shows the best results in our light extraction simulations. In this paper, SEM images of the samples will be presented together with measurements of excited crystals which show unrivalled performance for such scintillator samples

Effects of Photonic Crystals on the Light Output of Heavy Inorganic Scintillators

Photonic crystals (PhCs) are optical materials which can affect the propagation of light in multiple ways. In recent years PhCs contributed to major technological developments in the field of semiconductor lasers, light emitting diodes and photovoltaic applications. In our case we are investigating the capabilities of photonic crystal slabs with the aim to improve the performance of heavy inorganic scintillators. To study the combination of scintillators and PhCs we use a Monte-Carlo program to simulate the light propagation inside a scintillator and a rigorous coupled wave analysis (RCWA) framework to analyse the optical PhC properties. The simulations show light output improvements of a wide range of scintillating materials due to light scattering effects of the PhC slabs. First samples have been produced on top of 1.2 × 2.6 × 5 mm LSO (cerium-doped Lutetium Oxyorthosilicate, Lu_2SiO_5:Ce^3+) scintillators using electron beam lithography and reactive ion etching (RIE). Our samples show a 30-60% light output improvement when compared to unstructured reference crystals which is in close accordance with our simulation results. In addition, a theoretical investigation of the restrictions of the current PhC sample is given which concludes with prospects for improved future designs

Study of the Angular Distribution of Scintillation Photons

This paper presents a characterization method to experimentally determine the angular distribution of scintillation light. By exciting LYSO crystals with a radioactive source, we measured the light angular profiles obtained with samples of different geometries in different conditions of wrapping. We also measured the angular distribution of light emitting in glue and compared it with the one emitting in air. Angular distribution of light output of photonic crystals is also provided. Consistency of the measurements is verified with conventional light output measurements

Enhanced Scintillation Light Extraction Using Nanoimprinted Photonic Crystals

The extraction of scintillation light from a crystal with high efficiency and low time jitter is vital for realizing much-needed gains in the performance of numerous radiation detection and imaging instruments that are vital components in medical imaging, industrial, and homeland security applications for the detection, localization, and energy classification of X-rays, $\gamma$-rays, or neutrons. Nanostructures such as photonic crystals (PhCs) maximize extraction of usable scintillation light that is otherwise lost when a high refractive index (RI) scintillator is coupled to a photodetector with low RI window. The PhC gradually changes the RI between the scintillator and photodetector, thereby substantially improving the light extraction efficiency, as well as the energy resolution (ER) and timing resolution. Here, we report on improvements in the light extraction and ER of inorganic scintillators using PhCs nanoimprinted in high RI polymers. Details of the design, fabrication, and characterization of the PhCs, the high RI polymers, and their impact on scintillator performance are presented here

3D surface reconstruction by pointillism

The objective of this work is to infer the 3D shape of an object from a single image. We use sculptures as our training and test bed, as these have great variety in shape and appearance. To achieve this we build on the success of multiple view geometry (MVG) which is able to accurately provide correspondences between images of 3D objects under varying viewpoint and illumination conditions, and make the following contributions: first, we introduce a new loss function that can harness image-to-image correspondences to provide a supervisory signal to train a deep network to infer a depth map. The network is trained end-to-end by differentiating through the camera. Second, we develop a processing pipeline to automatically generate a large scale multi-view set of correspondences for training the network. Finally, we demonstrate that we can indeed obtain a depth map of a novel object from a single image for a variety of sculptures with varying shape/texture, and that the network generalises at test time to new domains (e.g. synthetic images)