We present an integral equation which generalizes a variety of known rendering algorithms. In the course of discussing a monte carlo solution we also present a new form of variance reduction, called Hierarchical sampling and give a number of elaborations shows that it may be an efficient new technique for a wide variety of monte carlo procedures. The resulting rendering algorithm extends the range of optical phenomena which can be effectively simulated.

/pdf/the-rendering-equation-123av1m206.pdf

The rendering equation

We are on the verge of ubiquitously adopting Augmented Reality (AR) technologies to enhance our percep- tion and help us see, hear, and feel our environments in new and enriched ways. AR will support us in fields such as education, maintenance, design and reconnaissance, to name but a few. This paper describes the field of AR, including a brief definition and development history, the enabling technologies and their characteristics. It surveys the state of the art by reviewing some recent applications of AR technology as well as some known limitations regarding human factors in the use of AR systems that developers will need to overcome.

/pdf/a-survey-of-augmented-reality-technologies-applications-and-3d9hf1tnc4.pdf

A Survey of Augmented Reality Technologies, Applications and Limitations

This paper presents a new reflectance model for rendering computer synthesized images. The model accounts for the relative brightness of different materials and light sources in the same scene. It describes the directional distribution of the reflected light and a color shift that occurs as the reflectance changes with incidence angle. The paper presents a method for obtaining the spectral energy distribution of the light reflected from an object made of a specific real material and discusses a procedure for accurately reproducing the color associated with the spectral energy distribution. The model is applied to the simulation of a metal and a plastic.

A reflectance model for computer graphics

This tutorial survey paper reviews several different models for light interaction with volume densities of absorbing, glowing, reflecting, and/or scattering material. They are, in order of increasing realism, absorption only, emission only, emission and absorption combined, single scattering of external illumination without shadows, single scattering with shadows, and multiple scattering. For each model the paper provides the physical assumptions, describes the applications for which it is appropriate, derives the differential or integral equations for light transport, presents calculation methods for solving them, and shows output images for a data set representing a cloud. Special attention is given to calculation methods for the multiple scattering model. >

Optical models for direct volume rendering

We propose a new rendering technique that produces 3-D images with enhanced visual comprehensibility. Shape features can be readily understood if certain geometric properties are enhanced. To achieve this, we develop drawing algorithms for discontinuities, edges, contour lines, and curved hatching. All of them are realized with 2-D image processing operations instead of line tracking processes, so that they can be efficiently combined with conventional surface rendering algorithms.Data about the geometric properties of the surfaces are preserved as Geometric Buffers (G-buffers). Each G-buffer contains one geometric property such as the depth or the normal vector of each pixel. By using G-buffers as intermediate results, artificial enhancement processes are separated from geometric processes (projection and hidden surface removal) and physical processes (shading and texture mapping), and performed as postprocesses. This permits a user to rapidly examine various combinations of enhancement techniques without excessive recomputation, and easily obtain the most comprehensible image.Our method can be widely applied for various purposes. Several of these, edge enhancement, line drawing illustrations, topographical maps, medical imaging, and surface analysis, are presented in this paper.

/pdf/comprehensible-rendering-of-3-d-shapes-3lxge6pa11.pdf

Comprehensible rendering of 3-D shapes

The effect of shadows and interreflection created by room obstructions is an important factor in the continuous tone representation of interiors. For indirect illumination, in most cases a uniform ambient light has been considered, even though the interreflection gives very complex effects with the shaded images.The proposed method for indirect lighting with shadows results in the following advanced points:1) The indirect illuminance caused by the surfaces of objects such as ceilings, floors, walls, desks, bookcases etc. gives added realism to images.2) The proposed method is suitable for every type of light source such as point sources, linear sources, and area sources.

Continuous tone representation of three-dimensional objects taking account of shadows and interreflection

Methods to display realistic clouds are proposed To display realistic images, a precise shading model is required: two components should be considered One is multiple scattering due to particles in clouds, and the other factor to be considered is sky light For the former, the calculation of cloud intensities has been assumed to be complex due to strong forward scattering However, this paper proposes an efficient calculation method using these scattering characteristics in a positive way The latter is a very significant factor when sky light is rather stronger than direct sunlight, such as at sunset/sunrise, even though sky light has been ignored in previous methods This paper describes an efficient calculation method for light scattering due to clouds taking into account both multiple scattering and sky light, and the modeling of clouds CR Categories and Subject Descriptors:

Display of clouds taking into account multiple anisotropic scattering and sky light

Studio spotlights produce dazzling shafts of light, while light scattered from fog illuminated by automobile headlights renders driving difficult. This is because the particles in the illuminated volume become visible by scattering light. A shading model for scattering and absorption of light caused by particles in the atmosphere is proposed in this paper. The method takes into account luminous intensity distribution of light sources, shadows due to obstacles, and density of particles. The intensity at a viewpoint is calculated by integration of light scattered by particles between the viewpoint and a given point on an object. The regions to be treated in this manner are localized by considering illumination volumes and shadow volumes caused by obstacles in the illumination volumes.

/pdf/a-shading-model-for-atmospheric-scattering-considering-1583ld9dg6.pdf

A shading model for atmospheric scattering considering luminous intensity distribution of light sources

DisplayofTheEarthTakingintoAccountAtmosphericScatteringTomoyuki Nishitaakao SiraiFukuy ama UniversityHigashimura-cho, Fukuyama, 729-02 JapanKatsumi TadamuraEihachiro NakamaeHiroshima Prefectural UnivNanatsuka-cho, Shoubara City, 727 JapanAbstractA method to display the earth as viewed from outer space(oraspaceship)isprop osed.Theintentionofthepap erisapplicationtospaceightsimulators(e.g.,reentrythe atmosphere) and the simulation of surveys of the earth(comparisons with observations from weather satellites andweather simulations); it is not for geometric mo deling of ter-rains and/or clouds viewed from the ground, but for display-ing the earth including the surface of the sea viewed fromouter space taking into account particles (air molecules andaerosols) in the atmosphere and water molecules in the sea.The ma jor p oints of the algorithm prop osed here are theecientcalculationofopticallengthandskylight,withlookup tables taking advantage of the facts that the earthis spherical, and that sunlight is parallel.CR Categories and Sub ject Descriptors:I.3.3 [Computer Graphics]:Picture/Image GenerationI.3.7 [Computer Graphics]: Three-DimensionalGraphics and RealismKey Words:Earth, Atmospheric Scattering, OpticalLength, Sky light, Color of Water, Photo-realism,Radiative Transfer1INTRODUCTIONResearch on image synthesis of realistic 3-D mo dels is oneof the most p opular elds thesedays.Displays of naturalscenes such as mountains,trees, sea, cloudshave b een at-tractively rendered, and an image synthesis of the earth hasalso beendevelop ed.Images of theearthare widely usedin movies or TV commercials, e.g., the CG library of earthimages[6] was recently released for use in this eld.Theseimages,however,arefo cusedontocreateattractiveimages without any requirement of physical based accuracy.However, physically-based images are required for the studyof the simulation of surveys of the earth, such as observationfrom weather satellites in comparison to weather simulation,and ight simulators in space.The color of the earth whenviewed from spacevaries accordingto the relationship b e-tween the view direction and the p osition of the sun.In thefamous words of the astronaut, \the earth was blue".Whenwe observe the earth from relatively close to the atmosphere,the atmosphere surrounding the earth app ears as blue, andthe atmosphere near the b oundary of the shadow due to thesun app ears red (i.e., sunset).The color of clouds also variesaccording to the sun's p osition.These phenomena are opti-cal e ects caused by particles in the atmosphere, and cannotb e ignored.The color of the surface of the sea is not uni-form, such as navy blue; it has various colors which dep endon incident light to the sea and absorption/scattering e ectsdue to water molecules.This pap er prop oses an algorithm of physically-based im-age synthesis of the earth viewed from space.The metho dprop osed here has the following advantages:(1)Calculationofthesp ectrumearthviewedthroughtheatmosphere;earthisilluminatedbydirectsunlightandskylighta ectedbyatmosphericscattering.(2)Calculation of the sp ectrum of the atmosphere takingaccount of absorption/scattering due to particles in theatmosphere.(3)Calculationofthesp ectrumonsurfaceseatakingintoaccountradiativetransferofwatermolecules.The ma jor parts in 1) and 2) are concerned with the calcu-lation of optical length and sky light. For these calculations,numerical integrations taking into account atmospheric scat-tering are required, but they are e ectively solved by usingseveral (various) lo okup tables making go o d use of the factsthat the shap e of the earth is a sphere and that sunlight isa parallel light.For 3), we show that an analytical solutionis available instead of numerical integrations.Inthefollowingsections,basicideaoflightingmo del forrenderingthecolorof theearthtakingintoac-count atmospheric scattering, rendering the color of clouds,andsp ectrumcalculationof theseais describ ed.Finally,several examples are demonstrated in order to show the ef-fectiveness of the metho d prop osed here.2BASICIDEASIn order to render the earth, the following elements shouldb e taken into account:a geometric mo del of the earth, theatmosphere(airmolecules,aerosols),sea,clouds,andthesp ectrum of the sunlight.This pap er discusses rendering an algorithm of the earth,theatmosphere,sea,andcloudsviewedfromouterspaceorvariousp ositionswithintheatmosphere;followingoptical characteristics should b e considered:(1)The color of the atmosphere:the atmosphere containsair molecules and aerosols, and scattered sunlight fromthoseparticles reachesthe viewp oint;the intensityofthelightreachingviewp oinisobtainedbyinte-grating scatteredlight from every particle on the ray,and the light scattered from the atmosphere around theearth also reaches this viewp oint.(2)The color of the earth's surface:the earth is illumi-natedby b oth direct sunlight and sky light.Sunlightis absorb ed when light passes through the atmosphere,and sky light consists of light scattered by particles inthe air.On the way, passingthroughthe atmospherethe light is attenuated, and its sp ectrum changes.1

Display of the earth taking into account atmospheric scattering

The degree of realism of the shaded image of a tree-dimensional scene depends on the successful simulation of shading effects. The shading model has two main ingredients, properties of the surface and properties of the illumination falling on it. Most previous work has concentrated on the former rather than the latter.This paper presents an improved version for generating scenes illuminated by point and linear light sources. The procedure can include intensity distributions for point light sources and output both umbrae and penumbrae for linear light sources, assuming thr environment is composed of convex polyhedra. This paper generalizes Crow's procedure for computing shadow volumes caused by the end points of the linear source results in an easy determination of the reions of penumbrae and umbrae on the face prior to shading calculation.This paper also discusses a method for displaying illuminance distribution on a shaded image aby using colored isolux contours.

http://nishitalab.org/user/nis/cdrom/p124-nishita.pdf

Eihachiro Nakamae

Papers

Continuous tone representation of three-dimensional objects taking account of shadows and interreflection

Display of clouds taking into account multiple anisotropic scattering and sky light

A shading model for atmospheric scattering considering luminous intensity distribution of light sources

Display of the earth taking into account atmospheric scattering

Shading models for point and linear sources