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Lightmaps from HDR Probes

Learn about lightmaps, precomputed illumination stored in texture memory for interactive walkthroughs. Explore related work, motivation for using Radiance, HDR probe capture, lightmap creation, and results. Discover how Radiance tools enhance rendering quality.

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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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