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Lightmaps from HDR Probes

Lightmaps from HDR Probes. Bernhard Spanlang VECG Group University College London b.spanlang@cs.ucl.ac.uk. Overview. What are Lightmaps Related Work Motivation for using Radiance Capturing HDR Probes Creating Lightmaps Results Conclusion. What are Lightmaps.

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Lightmaps from HDR Probes

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  1. Lightmaps from HDR Probes Bernhard Spanlang VECG Group University College Londonb.spanlang@cs.ucl.ac.uk

  2. Overview • What are Lightmaps • Related Work • Motivation for using Radiance • Capturing HDR Probes • Creating Lightmaps • Results • Conclusion

  3. What are Lightmaps • Precomputed illumination for interactive walkthroughs stored in texture memory • Only view independent surfaces (Lambertian) • Not vertex colour (usually Radiosity) • Can be stored in low-res texture for blending original texture if MultiTexture hardware

  4. Related Work • Radiosity solution (LightScape, stored in vertex colour, adaptive mesh subdivision) • Games Engines (eg. Quakes qrad) • Texture bakers in Lightwave and 3D Studio Max5, Brazil, FinalRender, etc.

  5. Motivation for using Radiance • Physically accurate rendering • Natural lighting with HDR • Postprocessing using Radiance tools(exposure, falsecolor, etc.) • Daylight simulationwith real surroundings

  6. Capturing HDR Probes • Camera response • Merging multiple exposures • For image alignment use a remotly controlled camera • Reflective sphere(Ball bearing) • Cubic mappingHDRShop • Removing Camera??? void glow mat_glow 0 0 4 1 1 1 0

  7. Lightmap Flow Chart

  8. Placing Radiance Cameras • In front of each triangle • Centre of surroundingrectangle • An orthographiccamera (-vtl)

  9. Rendering the Surfaces • Using Radiances’ view file (normally used for walkthrough animations) • Exploiting the ambient cache (-af file) • Allows parallel execution • Unfortunately there is no way to set the resolution in the view file. • Bug in Desktop Radiance –pa option ignored.

  10. Lightmap Composing • Aim is to merge all rendered surfaces to a single texture for efficient hardware rendering • Simplest approach: use pcompos placing the images next to and above each other. • UV coordinates of resulting VRML file have to reflect this. • ra_ppm –e converts Radiance file to ppm file at a specified exposure.

  11. Results(1/4) Cameras on Geometry Composed Lightmaps

  12. Results(2/4) Radiance Interactive Lightmaps

  13. Results(3/4) Lightmaps Radiance OpenGL

  14. Results(4/4) Radiance Lightmap

  15. Possible Improvements • Maintain connectivity of 3D triangles for 2D UV texture coordinates • Where not possible add extra pixels for interpolation (Sand pixels) • Triangle areas reflected in texture size • Coplanar surfaces represented by one lightmap element • Packing lightmap elements

  16. Summary • What are Lightmaps • Related Work • Motivation for using Radiance • Capturing HDR Probes • Creating Lightmaps • Results • Conclusion

  17. Questions • Contact :b.spanlang@cs.ucl.ac.ukwww.cs.ucl.ac.uk/staff/b.spanlang

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