3,507 research outputs found
Path-tracing Monte Carlo Library for 3D Radiative Transfer in Highly Resolved Cloudy Atmospheres
Interactions between clouds and radiation are at the root of many
difficulties in numerically predicting future weather and climate and in
retrieving the state of the atmosphere from remote sensing observations. The
large range of issues related to these interactions, and in particular to
three-dimensional interactions, motivated the development of accurate radiative
tools able to compute all types of radiative metrics, from monochromatic, local
and directional observables, to integrated energetic quantities. In the
continuity of this community effort, we propose here an open-source library for
general use in Monte Carlo algorithms. This library is devoted to the
acceleration of path-tracing in complex data, typically high-resolution
large-domain grounds and clouds. The main algorithmic advances embedded in the
library are those related to the construction and traversal of hierarchical
grids accelerating the tracing of paths through heterogeneous fields in
null-collision (maximum cross-section) algorithms. We show that with these
hierarchical grids, the computing time is only weakly sensitivive to the
refinement of the volumetric data. The library is tested with a rendering
algorithm that produces synthetic images of cloud radiances. Two other examples
are given as illustrations, that are respectively used to analyse the
transmission of solar radiation under a cloud together with its sensitivity to
an optical parameter, and to assess a parametrization of 3D radiative effects
of clouds.Comment: Submitted to JAMES, revised and submitted again (this is v2
A Survey of Ocean Simulation and Rendering Techniques in Computer Graphics
This paper presents a survey of ocean simulation and rendering methods in
computer graphics. To model and animate the ocean's surface, these methods
mainly rely on two main approaches: on the one hand, those which approximate
ocean dynamics with parametric, spectral or hybrid models and use empirical
laws from oceanographic research. We will see that this type of methods
essentially allows the simulation of ocean scenes in the deep water domain,
without breaking waves. On the other hand, physically-based methods use
Navier-Stokes Equations (NSE) to represent breaking waves and more generally
ocean surface near the shore. We also describe ocean rendering methods in
computer graphics, with a special interest in the simulation of phenomena such
as foam and spray, and light's interaction with the ocean surface
Color diversity index : the effect of chromatic adaptation
Common descriptors of light quality fail to predict the chromatic diversity produced by the same illuminant in different
contexts. The aim of this paper was to study the influence of the chromatic adaptation in the context of the development
of the color diversity index, a new index capable of predicting illuminant-induced variations in several types of images.
The spectral reflectance obtained from hyperspectral images of natural, indoor and artistic paintings, and the spectral
reflectance of 1264 Munsell surfaces were converted into the CIELAB color space for each of the 55 CIE illuminants
and 5 light sources tested. The influence of the CAT02 chromatic adaptation was estimated for each illuminant and for
each scene. The CIELAB volume was estimated by the convex hull method and the number of discernible colors was
estimated by segmenting the CIELAB color volume into unitary cubes and by counting the number of non-empty cubes.
High correlation was found between the CIELAB volume occupied by the Munsell surfaces and the number of
discernible colors and the CILEAB color volume of the colors in all images analyzed. The effects of the chromatic
adaptation were marginal and did not change the overall result. These results indicate that the efficiency of the new
illuminant chromatic diversity index is not influenced by chromatic adaptation
A note on the depth-from-defocus mechanism of jumping spiders
Jumping spiders are capable of estimating the distance to their prey relying only on the information from one of their main eyes. Recently, it has been shown that jumping spiders perform this estimation based on image defocus cues. In order to gain insight into the mechanisms involved in this blur-to-distance mapping as performed by the spider and to judge whether inspirations can be drawn from spider vision for depth-from-defocus computer vision algorithms, we constructed a three-dimensional (3D) model of the anterior median eye of the Metaphidippus aeneolus, a well studied species of jumping spider. We were able to study images of the environment as the spider would see them and to measure the performances of a well known depth-from-defocus algorithm on this dataset. We found that the algorithm performs best when using images that are averaged over the considerable thickness of the spider's receptor layers, thus pointing towards a possible functional role of the receptor thickness for the spider's depth estimation capabilities
Quantifying spatial, temporal, angular and spectral structure of effective daylight in perceptually meaningful ways
We present a method to capture the 7-dimensional light field structure, and
translate it into perceptually-relevant information. Our spectral cubic
illumination method quantifies objective correlates of perceptually relevant
diffuse and directed light components, including their variations over time,
space, in color and direction, and the environment's response to sky and
sunlight. We applied it 'in the wild', capturing how light on a sunny day
differs between light and shadow, and how light varies over sunny and cloudy
days. We discuss the added value of our method for capturing nuanced lighting
effects on scene and object appearance, such as chromatic gradients
Colorimetric Accuracy of Color Reproductions in the 3D Scenes
Color is a complex phenomenon that depends on the object, the observer and the light source, while the color reproduction additionally includes the surrounding conditions and it depends on the device that can either capture, display or print the reproduction. Colour accuracy is very important for digital reproduction of artistic work where colour represents essence of art. In our research, color reproductions of renderings of computer generated scenes, including an object, background and lights were assessed, and even more, colorimetric accuracy in renderings was analyzed. With assumption that shading in 3D computer generated scenes plays an important role in visual perception of rendered color, the colors were analyzed on renderings of shaded objects. It was determined that colorimetric accuracy depends on the position on rendered objects, either illuminated or shaded. Furthermore, it was discovered that color lightness and hue, light intensity and background influenced ΔRGB values
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