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Image Based Rendering

Image Based Rendering

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Image Based Rendering

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Presentation Transcript

  1. Image Based Rendering an overview

  2. Photographs • We have tools that acquire and tools that display photographs at a convincing quality level

  3. Photographs • We have tools that acquire and tools that display photographs at a convincing quality level, for almost 100 years now

  4. Sergei Mikhailovich Prokudin-Gorskii. A Settler's Family, ca. 1907-1915.

  5. Sergei Mikhailovich Prokudin-Gorskii. Tea Factory in Chakva. Chinese Foreman Lau-Dzhen-Dzhau. ca. 1907-1915.

  6. Sergei Mikhailovich Prokudin-Gorskii. The Emir of Bukhara, 1911.

  7. RGB in early 1900’s

  8. Plenoptic function • Defines all the rays • through any point in space (x, y, z) • with any orientation (θ, φ) • over all wavelenghts (λ) • at any given moment in time (t)

  9. IBR summary Representation of plenoptic function implicit explicit texture mapping panoramas view morphing geometric model 3D image warping ray databases

  10. Lightfield – Lumigraph approach[Levoy96, Gortler96] • Take all photographs you will ever need to display • Model becomes database of rays • Rendering becomes database querying

  11. Overview • Introduction • Lightfield – Lumigraph • definition • construction • compression

  12. Overview • Introduction • Lightfield – Lumigraph • definition • construction • compression

  13. From 7D to 4D • Static scene, t constant • λ approximated with RGB • consider only convex hull of objects, so the origin of the ray does not matter

  14. 4D Lightfield / Lumigraph

  15. Discreet 4D Lightfield

  16. Lightfield: set of images with COPs on regular grid

  17. or Lightfield: set of images of a point seen at various angles

  18. Depth correction of rays

  19. Overview • Introduction • Lightfield – Lumigraph • definition • construction • compression

  20. Overview • Introduction • Lightfield – Lumigraph • definition • construction • compression

  21. Construction from dense set of photographs

  22. Construction from sparse set of photographs camera positions acquisition stage blue screening space carving

  23. Filling in gaps using pull-push algorithm • Pull phase • low res levels are created • gaps are shrunk • Push phase • gaps at high res levels are filled using low res levels

  24. Overview • Introduction • Lightfield – Lumigraph • definition • construction • compression

  25. Overview • Introduction • Lightfield – Lumigraph • definition • construction • compression

  26. Compression • Large size uncompressed: 1.125GB • 32x32 (s, t) x 256x256 (u, v) x 6 faces x 3 B • Compression • jpeg + mpeg (200:1 to 6MB) • or vector quantization + entropy encoding

  27. Vector Quantization (VQ) • Principle • codebook made of codewords • replace actual word with closest codeword • Implementation • training on representative set of words to derive best codebook • compression: replacing word with index to closest codeword • decompression: retrieve indexed codeword from codebook

  28. Lightfield compression using VQ

  29. View morphing

  30. Motivation – rendering from images • Given • left image • right image • Create intermediate images • simulates camera movement [Seitz96]

  31. Previous work • Panoramas ([Chen95], etc) • user can look in any direction at few given locations • Image-morphing ([Wolberg90], [Beier92], etc) • linearly interpolated intermediate positions of features • input: two images and correspondences • output: metamorphosis of one image into other as sequence of intermediate images

  32. Previous work limitations • Panoramas ([Chen95], etc.) • no camera translations allowed • Image morphing ([Wolberg90], [Beier92], etc.) • not shape-preserving • image morphing is also a morph of the object • to simulate rendering with morphing, the object should be rigid when camera moves

  33. Overview • Introduction • Image morphing • View morphing • image pre-warping • image morphing • image post-warping

  34. Overview • Introduction • Image morphing • View morphing • image pre-warping • image morphing • image post-warping

  35. Image morphing • Correspondences

  36. Image morphing • Correspondences

  37. Image morphing • Correspondences

  38. Image morphing • Correspondences

  39. Image morphing • Correspondences • Linear interpolation P0 Pk Pn frame 0 frame k frame n

  40. Image morphing • Image morphing • not shape preserving

  41. Early IBR research Soft watch at moment of first explosion – Salvador Dali 1954

  42. Overview • Introduction • Image morphing • View morphing • image pre-warping • image morphing • image post-warping