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

In recent years, along with the extraordinary diffusion of the Internet and a growing need for personal verification in many daily applications, automatic signature verification is being considered with renewed interest. This paper presents the state of the art in automatic signature verification. It addresses the most valuable results obtained so far and highlights the most profitable directions of research to date. It includes a comprehensive bibliography of more than 300 selected references as an aid for researchers working in the field.

/pdf/automatic-signature-verification-the-state-of-the-art-68njryqnhw.pdf

Automatic Signature Verification: The State of the Art

A novel hybrid CNN-SVM classifier for recognizing handwritten digits

Scenario visualisation for participatory landscape planning—a study from Denmark

Sunlight and skylight are rarely rendered correctly in computer graphics. A major reason for this is high computational expense. Another is that precise atmospheric data is rarely available. We present an inexpensive analytic model that approximates full spectrum daylight for various atmospheric conditions. These conditions are parameterized using terms that users can either measure or estimate. We also present an inexpensive analytic model that approximates the effects of atmosphere (aerial perspective). These models are fielded in a number of conditions and intermediate results verified against standard literature from atmospheric science. Our goal is to achieve as much accuracy as possible without sacrificing usability.

http://www.cs.duke.edu/courses/cps124/spring08/assign/07_papers/p91-preetham.pdf

A practical analytic model for daylight

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

Photorealistic animated images are extremely effective for pre-evaluating visual impact of city renewal and construction of tall buildings. In order to generate a photorealistic image not only the direct sunlight but also skylight must be considered.



This paper proposes a method of high-fidelity image generation for photorealistic outdoor scenes based on the following ideas:



1
The intensity distribution of skylight taking account of scattering and absorption due to particles in the atmosphere which coincides with CIE standard skylight luminance functions is sought, and realistic images considering about spectrum distribution of skylight for any altitude of the sun can be easily and accurately displayed.

2
A rectangular parallelepiped with a specialized distribution of intensity simulating the skylight is introduced for efficient calculation of illumination due to skylight, and by employing a graphics hardware calculation of the skylight illuminance taking into account shadow effects is obtained with high efficiency; these techniques can be used to generate sequences of images, making animations possible at far lower calculation cost than previous methods.

Modeling of Skylight and Rendering of Outdoor Scenes

In this study, the implementation of an image processing technique on compute unified device architecture (CUDA) is discussed. CUDA is a new hardware and software architecture developed by NVIDIA Corporation for the general- purpose computation on graphics processing units. CUDA features an on-chip shared memory with very fast general read and write access, which enables threads in a block to share their data effectively. CUDA also provides a user- friendly development environment through an extension to the C programming language. This study focused on CUDA implementation of a representative optical flow computation proposed by Horn and Schunck in 1981. Their method produces the dense displacement field and has a straightforward processing procedure. A CUDA implementation of Horn and Schunck's method is proposed and investigated based on simulation results.

Optical Flow Computation on Compute Unified Device Architecture

We propose a fast approach for photo-realistic rendering of trees under various kinds of daylight, which is particularlyuseful for the environmental assessment of landscapes. In our approach the 3D tree models are transformedto a quasi-3D tree database registering geometrical and shading information of tree surfaces, i.e. their normalvectors, relative depth, and shadowing of direct sunlight and skylight, by using a combination of 2D buffers.Thus the rendering speed of quasi-3D trees depends on their display sizes only, regardless of the complexity oftheir original 3D tree models. By utilizing a two-step shadowing algorithm, our proposed method can create highquality forest scenes illuminated by both sunlight and skylight at a low cost. It can generate both umbrae andpenumbrae on a tree cast by other trees and any other objects such as buildings or clouds. Transparency, specularreflection and inter-reflection of leaves, which influence the delicate shading effects of trees, can also be simulatedwith verisimilitude.



Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three dimensional Graphics and Realism

Katsumi Tadamura

Papers

Display of the earth taking into account atmospheric scattering

Modeling of Skylight and Rendering of Outdoor Scenes

Optical Flow Computation on Compute Unified Device Architecture

Fast Photo‐Realistic Rendering of Trees in Daylight

Rendering of landscapes for environmental assessment