study Shading Based Surface Editing

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study Shading Based Surface Editing

  1. 1. Shading-Based Surface Editing<br />YotamGingold and Denis Zorin<br />New York University<br />SIGGRAPH08<br />
  2. 2. Abstract<br />A free-form surface modeling based on shading<br />
  3. 3. Outline<br />Introduction<br />Related Work<br />Shading Changed to Shape Changes<br />Overview of the System<br />Problem Formulation<br />Results<br />Conclusions and Future Work<br />
  4. 4. Introduction<br />
  5. 5. Surface Editing<br />2D UI  3D model & motion<br />Shape-from-shading (SfS) reconstruction<br />Sketch-basedmodeling<br />
  6. 6. Motivation<br />Indirection<br />User action vs. appearance change<br />Hard to deform<br />Smooth outline<br />Remove shadow<br />Reshape a highlight<br />
  7. 7. Purpose<br />A directly sketched-based surface modeling<br />Principle of continuity<br />if a user makes a small change in surface appearance, the resulting shape change should be small<br />
  8. 8. Challenges<br />standard formulation(Lambertian surface, orthographic projection, directional light) is known to be ill-posed.<br />
  9. 9. Challenges<br />Avoid small shading modification leading to large and unintuitive model changes<br />Preserve existing surface detail during editing<br />Region of interesting (ROI)during modifying<br />Realtime surface update<br />
  10. 10. Our major techniques <br />Design stroke-based 2D UI<br />SfS by solving a quadratic optimization <br />
  11. 11. Related Work<br />
  12. 12. Related Work<br />Shape-Preserving<br />[Sorkine et al. 04]<br />[Yu et al. 04]<br />[Wardetzky et al. 07]<br />Shape-from-Shading<br />[Rushmeier et al. 03]<br />[Prados 04]<br />Sketch-based modeling<br /> [Igarashi et al. 99]<br />[Cheutet et al. 04]<br />[Lawrence and Funkhouser 04]<br />[Kara et al. 06]<br /> [Karpenko and Huges 06]<br />[Nealen et al. 07]<br />Silhouette Editing<br /> [DeCarloet al. 03]. Suggestive contour<br /> [Nealen et al.05], <br />[Zimmermann et al. 07]<br />
  13. 13. Shape-from-Shading Reconstruction<br />The recover of shape form a gradual variation of shading in the image<br />z<br />x<br />y<br />Z(x,y)<br />
  14. 14. Shading Changes to Shape Changes<br />Guarantee the stability of surface changes and satisfying boundary constraints<br />
  15. 15. a continuous solution<br />an approximate solution<br />all solutions are discontinuous<br />(with either one or two sides fixed)<br />
  16. 16. Instability near highlights<br />Conclusion<br />Smooth deformation can’t erase highlight<br />A large change in the surface shape<br />Strategy<br />Terminate erasing strokes at highlight<br />Highlight removal <br />
  17. 17. Slope ambiguity<br />Convex-concave ambiguity<br />slope ambiguity<br />Strategy- choose the slope to change the surface the least <br />
  18. 18. Overview of the System<br />
  19. 19. I(q) = ρ(n(p))<br />Only one light source<br />pl<br />pv<br />Iimage<br />q<br />q<br />n<br />v<br />L<br />Lambertian & glossy <br />reflection model , n(p)<br />I<br />p<br />Msurface<br />User modified<br />~Msurface<br />~I<br />
  20. 20. Lambertianand Glossy Reflection Model<br />β is the degree of glossiness<br />pis the Phong exponent<br /> h = (v+l) / |v+l|<br />
  21. 21. Iimage<br />I(q) = ρ(n(p))<br />Only one light source<br />C<br />pl<br />q<br />q<br />v<br />n<br />L<br />q = P(p)<br />~I<br />Lambertian & glossy <br />reflection model , n(p)<br />p<br />P-1(C)<br />Msurface<br />
  22. 22. brush<br />Shading modification brush<br />Silhouette brush<br />Highlight motion brush <br />ROI pen<br />attributes of brush<br /><ul><li>Opacity
  23. 23. Smoothness
  24. 24. Width</li></li></ul><li>Stroke attributes – α (opacity)<br />Replace mode<br />Multiply mode<br />
  25. 25. Stroke attributes – f (softness)<br />
  26. 26. Stroke attributes – w (width)<br />
  27. 27. Problem Formulation<br />
  28. 28. Surface Optimization Function<br />Detail-preserving<br />Preserving appearance outside strokes<br />Stroke constrain<br />Match the modified surface under the stroke <br />Detail-preserving<br />Stroke constrain<br />
  29. 29. Detail-preserving<br />[Yu et al. 04]<br />
  30. 30. The vector Laplacianis the normal scaled by the mean curvature [Sorkine et al. 04]<br />If the surface changes remain close to isometric, the Laplacian operator does not change [Wardetzky et al. 07]. The Laplacian difference <br />ΔM : Laplace-Beltrami operator<br />H: mean curvature<br />
  31. 31. Small triangle distortion <br />? = isometric deformations<br />
  32. 32. Hypothesis<br />If the triangle distortion stays small, one can view the Laplacian difference energy as a weighted normal change penalty<br />(detail-preserving)<br />
  33. 33. Hypothesis<br />Want the normals to retain their spatial direction with respect to the viewing direction and the light source<br />Strokes constrain the rotation of normals<br />Find min. αs.t. ρ(n(α)) = Itrg<br />
  34. 34. Stroke smoothness and thick strokes<br />Weaken the link between stroke and the rest of surface<br />(detail-preserving)<br />C<br />P(x0)<br />h(r)<br />x0<br />r<br />w/2<br />-w/2<br />(1-c)/d = f <br />
  35. 35. Detail-preserving<br />(detail-preserving)<br />
  36. 36. Stroke constrain<br />
  37. 37. xj<br />xi<br />Constrain the new tangent<br />
  38. 38. Constraint the projected position of <br />P(p) = P(ap1 + (1-a) p2)<br />C<br />P(p1)<br />xj<br />P(p)<br />P(p2)<br />xi<br />p<br />p1<br />p2<br />
  39. 39. Realization of Stroke Attributes<br />Stroke smoothness and thick strokes<br />Silhouette strokes<br />Interaction with highlights<br />Highlight motion strokes<br />
  40. 40. Silhouette strokes<br />No opacity α, no value Iv<br />Smoothness<br />
  41. 41. Interaction with highlights<br />Cross a highlight<br />Local max of ρ(n) <br />  Large changed range, discontinuity<br /> Terminate stroke at the highlight <br />
  42. 42. Highlight motion strokes<br />Xnewtrg of <br />after<br />before<br />
  43. 43. Adaptive refinement<br /><ul><li>Adaptive √3-subdivision</li></ul>441 vrtx.<br />1302 vrtx.<br />
  44. 44. Result<br />MacBook Pro + 2GHx Intel Core Duo processor<br />Performance issues<br />Stroke size, ROI setting, mesh size, degree of adaptive refinement<br />
  45. 45. Conclusions and Future Work<br />Shading-based surface editing<br />A direct and intuitive UI to modify surface<br />Intuitive shading strokes <br />Future work<br />Blur stroke<br />
  46. 46. END<br />
  47. 47. END<br />

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