Understanding exposure for reverse tone mapping

High dynamic range (HDR) displays are capable of providing a rich visual experience by boosting both luminance and contrast beyond what conventional displays can offer.We envision that HDR capture and display hardware will soon reach the mass market and become mainstream in most fields, from entertainment to scientific visualization. This will necessarily lead to an extensive redesign of the imaging pipeline. However, a vast amount of legacy content is available, captured and stored using the traditional, low dynamic range (LDR) pipeline. The immediate question that arises is: will our current LDR digital material be properly visualized on an HDR display? The answer to this question involves the process known as reverse tone mapping (the expansion of luminance and contrast to match those of the HDR display) for which no definite solution exists. This paper studies the specific problem of reverse tone mapping for imperfect legacy still images, where some regions are under- or overexposed. First, we show the results of a psychophysical study compared with first-order image statistics, in an attempt to gain some understanding in what makes an image be perceived as incorrectly exposed; second, we propose a methodology to evaluate existing reverse tone mapping algorithms in the case of imperfect legacy content

Structural optimization of 3D masonry buildings

In the design of buildings, structural analysis is traditionally performed after the aesthetic design has been determined and has little influence on the overall form. In contrast, this paper presents an approach to guide the form towards a shape that is more structurally sound. Our work is centered on the study of how variations of the geometry might improve structural stability. We define a new measure of structural soundness for masonry buildings as well as cables, and derive its closed-form derivative with respect to the displacement of all the vertices describing the geometry. We start with a gradient descent tool which displaces each vertex along the gradient. We then introduce displacement operators, imposing constraints such as the preservation of orientation or thickness; or setting additional objectives such as volume minimization.Shell Oil CompanyNatural Sciences and Engineering Research Council of Canada (PGS Program)Samsung Scholarship Foundatio

Robust iso-surface tracking for interactive character skinning

International audienceWe present a novel approach to interactive character skinning, which is robust to extreme character movements, handles skin contacts and produces the effect of skin elasticity (sliding). Our approach builds on the idea of implicit skinning in which the character is approximated by a 3D scalar field and mesh-vertices are appropriately re-projected. Instead of being bound by an initial skinning solution used to initialize the shape at each time step, we use the skin mesh to directly track iso-surfaces of the field over time. Technical problems are two-fold: firstly, all contact surfaces generated between skin parts should be captured as iso-surfaces of the implicit field; secondly, the tracking method should capture elastic skin effects when the joints bend, and as the character returns to its rest shape, so the skin must follow. Our solutions include: new composition operators enabling blending effects and local self-contact between implicit surfaces, as well as a tangential relaxation scheme derived from the as-rigid-as possible energy to solve the tracking problem

Computational pattern making from 3D garment models

We propose a method for computing a sewing pattern of a given 3D garment model. Our algorithm segments an input 3D garment shape into patches and computes their 2D parameterization, resulting in pattern pieces that can be cut out of fabric and sewn together to manufacture the garment. Unlike the general state-of-the-art approaches for surface cutting and flattening, our method explicitly targets garment fabrication. It accounts for the unique properties and constraints of tailoring, such as seam symmetry, the usage of darts, fabric grain alignment, and a flattening distortion measure that models woven fabric deformation, respecting its anisotropic behavior. We bootstrap a recent patch layout approach developed for quadrilateral remeshing and adapt it to the purpose of computational pattern making, ensuring that the deformation of each pattern piece stays within prescribed bounds of cloth stress. While our algorithm can automatically produce the sewing patterns, it is fast enough to admit user input to creatively iterate on the pattern design. Our method can take several target poses of the 3D garment into account and integrate them into the sewing pattern design. We demonstrate results on both skintight and loose garments, showcasing the versatile application possibilities of our approach.</jats:p