This paper introduces a simple model for subsurface light transport in translucent materials. The model enables efficient simulation of effects that BRDF models cannot capture, such as color bleeding within materials and diffusion of light across shadow boundaries. The technique is efficient even for anisotropic, highly scattering media that are expensive to simulate using existing methods. The model combines an exact solution for single scattering with a dipole point source diffusion approximation for multiple scattering. We also have designed a new, rapid image-based measurement technique for determining the optical properties of translucent materials. We validate the model by comparing predicted and measured values and show how the technique can be used to recover the optical properties of a variety of materials, including milk, marble, and skin. Finally, we describe sampling techniques that allow the model to be used within a conventional ray tracer.

The reflection of light from most materials consists of two major terms: the specular and the diffuse. Specular reflection may be modeled from first principles by considering a rough surface consisting of perfect reflectors, or micro-facets. Diffuse reflection is generally considered to result from multiple scattering either from a rough surface or from within a layer near the surface. Accounting for diffuse reflection by Lambert's Cosine Law, as is universally done in computer graphics, is not a physical theory based on first principles. This paper presents

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An important component that has been missing from image synthesis is the effect of weathering. In this paper, we present an approach for the modeling and rendering of one type of weathering --- metallic patinas. A patina is a film or incrustation on a surface that is produced by the removal of material, the addition of material, or the chemical alteration of a surface. Oxidation, sulphidization, and painting are examples of phenomena that produce patinas. We represent a surface as a series of layers. Patinas are simulated with a collection of operators, such as "coat," "erode," and "polish, " which are applied to the layered structure. The development of patinas is modulated according to an object's geometry and local environmental factors. We introduce a technique to model the reflectance and transmission of light through the layered structure using the Kubelka-Munk model. This representation yields a model that can simulate many aspects of the time-dependent appearance of metals as...

This article aims to unify these models into a single framework through an adequate mathematical formulation. We'll successively integrate into the model one phenomenon after the other. The resulting unified physical model should be able to predict the diffuse reflection spectrum of color samples illuminated by a diffuse light source. In this study, we limit ourselves to predicting uniform color samples made of one or several superposed ink layers. We're currently investigating an extension of the proposed model for halftoned samples

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The light reflected from a surface depends on the scene geometry, the incident illumination and the surface material. One of the properties of the material is its albedo r(l) and its variation with respect to wavelength. The albedo of a surface is purely a physical property. Our perception of albedo is commonly referred to as colour. This paper presents a novel methodology for extracting the albedo of the various materials in the scene independent of incident light and scene geometry. A scene is captured under different narrow-band colour filters and the spectral derivatives of the scene are computed. The resulting spectral derivatives form a spectral gradient at each pixel. This spectral gradient is a normalized albedo descriptor which is invariant to scene geometry and incident illumination for diffuse surfaces.

A new spectral colour prediction model for a fluorescent ink printed on paper is presented. It is based on our previous work on transparent support and on a new mathematical formalism which generalizes the Kubelka-Munk theory. The printed paper is modelized by means of three matrices: an interface correction matrix, a matrix exponential modelizing the layer which contains the fluorescent ink, and a reflection matrix caracterising the substrate. The interface correction matrix allows to take multiple reflections into account by operating the Saunderson correction. These matrices are related to physical properties of ink and paper which must be measured: the transmittance spectra, the quantum yields, the absorption bands and the emission spectra of the fluorescent inks, and the reflection properties of the paper. Our new model can predict the reflection spectra of uniform samples for different ink concentrations and under different illuminants. It is applied successfully to predict the spectra of real samples with an average prediction improvement of about in comparison with Beer's law.

The formation of chromophores and leucochromophores during the manufacturing of thermomechanical pulp (TMP) has been investigated. As analytical tools, advanced UV-VIS and NMR spectroscopy have been used. With the exception of some pilot plant scale refining experiments, that were carried out at Valmet Fibertech (Sundsvall), the work has been conducted at the Royal Institute of Technology (Stockholm). When wood is converted into TMP, both chromophoric and leucochromophoric structures are formed. The greatest changes in the light absorption coefficient spectrum of the material takes place in the first refining stage, with a predominant increase in the region below 400 nm. Addition of a mixture of DTPA and sodium sulphite to the wood, before refining, results in a decreased formation of leucochromophoric structures, however. The increase in light absorbance, caused by the refining of wood, does not appear to be correlated to any conversion of β-1 structures into stilbenes, despite an observed reduction in the amount of a known dienone structure, which act as a precursor for β-1