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Synthetic Object Rendering Using Global Illumination and HDR Photography

This paper explores a method for seamlessly integrating synthetic objects into real-world scenes with accurate lighting, utilizing High Dynamic Range (HDR) radiance maps and Global Illumination. The process involves dividing the scene into distant and local parts, generating accurate lighting for synthetic objects, and employing a differential rendering approach. The framework presented aims to bridge traditional graphics with image-based techniques, offering a comprehensive solution for enhancing visual effects, architectural simulation, and more.

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Synthetic Object Rendering Using Global Illumination and HDR Photography

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  1. Rendering Synthetic Objects into Real Scenes: Bridging Traditional and Image-based Graphics with Global Illumination and High Dynamic Range Photography Paul Debevec, University of California at Berkley

  2. Motivation • Visual Effects • Adding synthetic actors/props • Architectural simulation • Adding buildings to landscapes

  3. Related Work • Previous methods used to insert synthetic objects into real scenes • Drawing • Environment mapping • Approximate geometric model and lighting • Global illumination algorithms • Recovery of HDR radiance maps from photographs

  4. Related Work • High Dynamic Range refers to the range of brightness values present in a scene • Eyes, photos, displays, all capture a limited, non-linear range 1000:1 100:1 Everyday brightness range (about 1012:1) Source: Microsoft Developers Network

  5. Related Work • Why is this a problem? • Limited brightness range results in lost scene detail from saturation and/or underexposure • OK for traditional image use Photos from OpenEXR by LucasFilm, LTD. http://www.openexr.com/samples.html

  6. Related Work • What about image-based lighting? • Photo pixel values are not representative of relative Radiance in the scene Images by Paul Debevec, 98

  7. Related Work • Solution: Take multiple photos with varying shutter speeds and ‘combine’ somehow to create accurate relative radiance maps Images by Paul Debevec, 98

  8. Related Work • Is HDR really important?

  9. Method • Divide the scene into three parts

  10. Method • Distant Scene • Light-based model • Required to provide correct incident illumination to local/synthetic objects from desired viewpoint • Assumed that no light from the model will affect the distant scene • Any level of geometric detail wanted

  11. Method • Local Scene • Material-based model (has BRDF) • Must approximate the real scene local to the position of the synthetic objects • ‘Local’ means photometrically local • ‘Approximate’ means geometrically AND photometrically representative of the real scene

  12. Method • Synthetic Objects • Complete materials-based models of elements that are to be inserted into the scene • Geometric and lighting information • Any shape and material supported by the global illumination method that you plan to use

  13. Method • Compositing using a light probe • One method to create the distant scene from a real location • Uses a metal sphere and a camera to gather light from a point

  14. Method • Compositing using a light probe • This light is mapped onto the distant scene geometry and used to calculate the lighting • Lighting is calculated with global illumination

  15. Method • Results

  16. Method • Problem with the current definition of the local scene • We said that it must approximate the material of the real scene • It can be really hard to get the BRDF/material of a real object! • Can we modify the local scene so it doesn’t require this?

  17. Method • Local Scene 2 (Differential Rendering) • Approximate the material of the scene to within reason (not exact) • Render with and without your synthetic objects and calculate the difference • Add that difference back into the original image

  18. Method • Difference between local scene render with and without synthetic objects - =

  19. Results

  20. Conclusion • This paper presented a framework for rendering synthetic objects into real world environments with real lighting • High Dynamic Range radiance maps • Global Illumination • Distant and local scenes, synthetic objects • Differential rendering

  21. Future Work • Method to generate boundary between distant and local scene • More efficient global illumination

  22. Comments • Pros • Open framework • Good results • Cons • Hard to decide what local scene should be! • Local scene can be very complicated

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