Rendering Synthetic Objects into Real-World Scenes by Paul Debevec SIGGRAPH 98 ConferenceIntroductionSlide 3Slide 4Slide 5Recording light measurementsRecording light measurementsSlide 8Slide 9Slide 10Adding synthetic objects to scenesSlide 12Slide 13Three Components of General MethodCompositing objects into sceneMapping from probe to scene modelMapping from probe to scene model - ProblemsSlide 18Slide 19Slide 20Slide 21Slide 22Improving quality with differential renderingSlide 24Slide 25Slide 26BRDFSlide 28Estimating the local scene BRDFSlide 30Slide 31Slide 32Compositing ResultsCompositing ResultsConclusionRendering Synthetic Objects into Real-World Scenes by Paul DebevecSIGGRAPH 98 ConferencePresentedByJustin N. Rogers for Advanced Comp Graphics Spring 2002IntroductionRealistically adding synthetic objects to real-world scenes is difficultInterplay of light between objects and surroundings must be consistentShould cast shadows on surroundingsShould appear in reflectionsShould refract, focus, and emit light similarly as real objects wouldIntroductionCurrent techniques manually model light sourcesphotograph a reference object and use guide for lighting environmentProblems with current techniquesrequires considerable hand-refinementhard to simulate effects of indirect illumination from environmentIntroductionRelated WorkReflection Mapping produces realistic results for mirror-like objectsDisadvantages – doesn’t account for objects casting light or shadows on the environmentUse of geometric models of environment local to object to compute shadows from various light sourcesDisadvantages – requires complete knowledge about each light source in sceneDisadvantages – doesn’t account for diffuse reflection from the sceneIntroductionRelated WorkRecent developments have produced algorithms and software packages that realistically simulate lightingIncludes indirect lighting with diffuse and specular reflectionsRecording light measurementsIllumination of objects with actual samples of light from real scenesProvides a unified and physically accurate alternative to replicating incidental illuminationDifficultiesRecording light in scenes is difficult due to high dynamic range that usually exists.Due to fact light sources are usually concentratedHowever the direct light from light sources and indirect light from the environment are important parts of the illumination solution.Recording light measurements Conventional imaging equipment is used to derive radiance maps from scenes F-stop or f-number is used to record the dynamic range of light and form radiance mapsf-stop refers to the maximum lens apeturef-stop also refers to the specific apeture selected for optimal brightnessSynthetic objects are illuminated using the radiance mapsAn omnidirectional radiance map. This full dynamic range lighting environmentwas acquired by photographing a mirrored ball balanced on the cap of a pin sitting on a table. The three views of this image are adjusted to (a)+0 stops(b)-3.5 stops, and (c)-7.0 stops show that the full dynamic range of the scene hasbeen captured without saturation.Illuminating synthetic objects with real light (Top row:a,b,c,d,e) With fulldynamic range measurements of scene radiance from previous slide.(Bottom row:f,g,h,i,j) With low dynamic range information from a singlephotograph of the ball. The right sides of images (h,i,j) have been brightenedby a factor of six to allow qualitative comparison to (c,d,e). The high dynamicrange measurements of scene radiance are necessary to produce proper lightingon the objects.Synthetic objects lit by two different environments (a) A collection of objectsis illuminated using the radiance information from the previous radiance map (b) The same objects are illuminated by radiance information obtained in an outdoor environment on an overcast day. Radiance maps used in illuminationare displayed in the upper left-hand corner of the images.Adding synthetic objects to scenesScene is broken into three components: the distant scene, the local scene, and the synthetic objects.Global illumination is used to simulate the interplay of light between the three components.light from the distant scene is ignoredAdding synthetic objects to scenesDistant SceneRadiates light towards the local scene and synthetic objects, but ignores light reflected to itLocal SceneContains the surfaces that will interact with the synthetic objectsFull geometry and reflectance properties must be known to ensure proper interactionsAdding synthetic objects to scenesSynthetic ObjectsMay consist of a variety of shapes and materialsShould be placed in desired correspondence to the local sceneAfter the three components are modeled and positioned then the global illumination software is used to produce renderings.Three Components of General MethodDistant Scene light-based(no reflectance model)Local Scene estimated reflectance model Synthetic Objectsknown reflectance modellightCompositing objects into scene Constructing light-based model w/light probeLight-based model of distant scene needs to appear correctly near synthetic objects.Used to calculate incident light to illuminate synthetic objectsObtaining radiance map of distant scenephotograph a spherical, mirror-like object near the location of the synthetic object radiance measurements are mapped onto geometry of distant sceneMapping from probe to scene modelCorrect mapping between coordinates on the ball and ray in the world requires that the ball position relative to the camera, the size of the ball, and the camera parameters such as its location in the scene and focal length be recordedThe data from a single ball image will display some artifacts. (1)The camera will be visible (2)The ball interacts with the scene: the ball (and its support) can appear in reflections, cast shadows, and can reflect light back onto surfaces (3)The ball won’t reflect the scene directly behind it, and will provide a poor sample of the nearby area.Mapping from probe to scene model - ProblemsCareful positioning of the ball and camera will cause these effects to be minimized and they won’t have a dramatic impact on the final renderings. If the artifacts are significant then the images can be altered by (1)manually in an image-editing software or by (2)combining
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