Estimating Reflectance Layer from A Single Image: Integrating Reflectance Guidance and Shadow/Specular Aware Learning

Estimating reflectance layer from a single image is a challenging task. It becomes more challenging when the input image contains shadows or specular highlights, which often render an inaccurate estimate of the reflectance layer. Therefore, we propose a two-stage learning method, including reflectance guidance and a Shadow/Specular-Aware (S-Aware) network to tackle the problem. In the first stage, an initial reflectance layer free from shadows and specularities is obtained with the constraint of novel losses that are guided by prior-based shadow-free and specular-free images. To further enforce the reflectance layer to be independent from shadows and specularities in the second-stage refinement, we introduce an S-Aware network that distinguishes the reflectance image from the input image. Our network employs a classifier to categorize shadow/shadow-free, specular/specular-free classes, enabling the activation features to function as attention maps that focus on shadow/specular regions. Our quantitative and qualitative evaluations show that our method outperforms the state-of-the-art methods in the reflectance layer estimation that is free from shadows and specularities.Comment: Accepted to AAAI202

Simulador de imágenes acústicas mediante elementos finitos utilizando cámaras RGB depth y sensores LiDAR 3D

El objetivo de este proyecto es analizar y comparar las imágenes acústicas reales obtenidas con un sistema de adquisición acústico basado en un array extenso de micrófonos frente a las imágenes acústicas generadas por un simulador implementado en LabVIEW. El simulador se basa en un modelo acústico pulso-eco, donde un transmisor genera una señal pulsada que se refleja en cada punto del objeto bajo estudio y es recogida por cada uno de los sensores del array de micrófonos. De este modo, el simulador genera como resultado señales 2D a partir de la nube de puntos que forman la superficie del objeto. Esta nube de puntos se obtiene mediante una cámara LiDAR o mediante un generador sintético de objetos. Finalmente, con las señales 2D obtenidas y haciendo uso de la herramienta software ViSAM© desarrollada por el Grupo de Procesado en Array de la Universidad de Valladolid, se obtienen las imágenes acústicas sintetizadas mediante técnicas de conformación de haz.The objective of this project is to analyze and compare the real acoustic images obtained with an acoustic acquisition system based on an extensive array of microphones against the acoustic images generated by a simulator implemented in LabVIEW. The simulator is based on a pulse-echo acoustic model, where a transmitter generates a pulsed signal that is reflected at each point of the object under study and is collected by each of the sensors in the microphone array. This way, the simulator generates as a result 2D signals from the cloud of points that form the surface of the object. This point cloud is obtained by a LiDAR camera or by a synthetic object generator. Finally, with the 2D signals obtained and making use of the ViSAM© software tool developed by the Array Processing Group of the University of Valladolid, the acoustic images synthesized by beamforming techniques are obtained.Departamento de Teoría de la Señal y Comunicaciones e Ingeniería TelemáticaGrado en Ingeniería de Tecnologías de Telecomunicació

Effects of Microstructural Properties on Structural Color of Self-Assembled Colloidal Crystals

This dissertation examines the relationship between colloidal microstructural properties and structural color, to guide the design of optical materials. Colloidal microstructures can interact with light to produce structural color, which is not prone to environmental degradation. The high stability of structural color provides great potential for optical applications such as coatings and displays. Previous studies in structural color from colloidal systems have primarily focused on controlling structural color wavelength by changing the dielectric periodicity of the material. However, the connection between colloidal microstructural properties and structural color reflectivity – particularly its magnitude – remains unclear. In this dissertation, we systematically and quantitatively investigate the effects of crystal thickness, defect density and structure, irregularity of particle size, and particle shape on structural color by experiment and simulation. The relationships can be applied to designing novel materials with tailored structural color properties. First, we report how film thickness, defect density, and defect type in colloidal crystals quantitatively affect their structural color reflectivity. Colloidal crystals with different thicknesses are fabricated by self-assembling monosized polystyrene microspheres via solvent evaporation. We find that the structural color reflectivity increases as a function of the crystal thickness, until a plateau is reached at 78.8 ± 0.9%. We also model crystals via molecular dynamics and simulate their reflection spectra by the finite-difference time-domain method. The simulation results show that the reduction in reflectivity scales with increased defect density and that stacking fault tetrahedra are most efficient in disrupting structural color. These findings can guide the efficient design of structural color materials and support defect engineering in colloidal crystals. Second, we evaluate the role of irregular-sized spherical particles in determining crystal quality and structural color reflectivity. By evaporative self-assembly and molecular dynamics simulation, we control the volume fraction of irregular-sized particles – by choosing particles that are either larger or smaller than the base colloids comprising the self-assembled crystals. Then we quantify crystal quality from analysis of diffraction patterns obtained by Fast Fourier transform of the scanning electron microscope images. We find that small irregular particles are more detrimental to crystal quality and structural color reflectivity than large irregular particles. When incorporated with 10 vol% of irregular particles, the reflectivity of crystal films with large (small) irregular particles decreases by 18.4% ± 5.6% (27.5 ± 5.8%), and crystal quality reduced by 40.0 ± 4.5% (48.8 ± 6.0%). This study can be applied to predict the level of irregular-sized particles that can be tolerated in structural color materials at a specified reflectivity. Finally, we explore the effect of particle anisotropy on structural color reflection from discoid packings. We prepare discoidal particles that vary in shape anisotropy and particle size by uniaxial compression of spheres. Discoids are self-assembled by evaporation into dense discoid packings, which exhibit non-iridescent structural colors. This coloration is a combination of backscattering and multilayer reflection. We find that the multilayer reflection displays progressively smaller peak height and broader bandwidth as the discoids become more anisotropic. In addition, Monte Carlo simulation is used to produce comparable discoid structures. The density profiles of the simulated structures in the wall-normal direction demonstrate that discoids with a higher shape anisotropy assemble into more disordered structures, which explains the less intense structural color. Our findings demonstrate that tunable geometries of discoids increase the opportunities for spectral control of non-iridescent structural color materials.PHDMacromolecular Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/170049/1/ltianyu_1.pd