1. X-Toon: An Extended Toon Shader Pascal Barla, Joelle Thollot ARTIS GRAVIR/IMAGE INRIA Lee Markosian University of Michigan

2. Outline Introduction Introduction Tone Detail Shape Detail Discussion and Future Work

3. Introduction Toon shading: simple but effective A dot product between a light vector and surface normal 1D texture “dark” to “light” regions 2 ~ 3 constant color (comics, traditional animation) Can be implemented efficiently via vertex and fragment programs on modern GPUs

4. Limitation Does not reflect the “importance” or desired level of detail of a surface Depth-of-field View-independent View-dependent highlights, view-dependent backlighting effect Full accuracy A degree of abstraction so that small shape details are omitted

5. X-Toon Supports view-dependent Tone detail Tone varies with depth or orientation relative to the camera 1D texture → 2D texture Shape detail Using a modified normal field defined by interpolating between normal of the original shape and normal of a highly abstracted shape

6. Outline Introduction Tone Detail Tone Detail Shape Detail Discussion and Future Work

7. Tone Detail Toon texture: 1D → 2D Horizontal: n ‧ l (lambertian shading) Vertical: tone detail This axis corresponds to its own 1D toon texture Attribute maps Control the tone detail and provide functions View-dependent attributes Depth-based attribute maps Orientation-based attribute maps ( LODs, aerial perspective, depth-of-field, backlighting, specular highlights)

8. Outline Introduction Related Work Tone Detail Tone Detail Depth-based attribute mapping Depth-based attribute mapping Orientation-based attribute mapping Shape Detail Discussion and Future Work

9. “Depth” of A Point in 3D Distance between the eye and p Depth-of-field Distance along the focal axis LODs, Aerial perspective

10. User-specified Parameters z min the distance at which the detail starts decreasing r > 1 the scale factor that defines the coarsest detail at distance z max = r*z min z min z max = r* z min

11. Perspective Projection Formula for detail mapping r z min z max = r* z min

12. Depth-of-Field Formula for detail mapping D =

13. Depth-based LOD Effects smooth out the shading with distance mimic a discrete LOD behavior make a receding shadow effect

14. Focus-based Detail Map blurred texture a texture where contrast and opacity are decreased

15. Aerial Perspective

16. Outline Introduction Tone Detail Tone Detail Depth-based attribute mapping Orientation-based attribute mapping Orientation-based attribute mapping Shape Detail Discussion and Future Work

17. Near-silhouette Attribute Mapping Attribute map based on the orientation of the surface with respect to the observer View-dependent effect Fading of near-silhouette regions, or brightening and coloring of near-silhouette regions to suggest a virtual “backlight” Near-silhouette attribute mapping (controls the magnitude of the effect)

18. Near-silhouette Abstraction & Backlighting

19. Specular Highlights View-dependent effect Model various material highlights Depending on the chosen 2D texture control the profile of the highlight (smoothness, width, alpha) so that it is correlated with the underlying tone e.g., plastics or metals Highlight attribute mapping (Phong highlight model) (shininess coefficient)

20. Highlights

21. Outline Introduction Tone Detail Shape Detail Shape Detail Discussion and Future Work

22. Abstracted Shape Geometric map Modify the surface normal field Map the input mesh to an “abstracted shape” lower bound for shape detail has a direct correspondence with the input surface Blending parameter Controls how the shader interpolates Important property Keeping the original silhouettes of the model

23. Four Types of Abstracted Shape

24. Outline Introduction Tone Detail Shape Detail Discussion and Future Work Discussion and Future Work

25. Performance Extensions to the original toon shader, aimed at retaining its simplicity while allowing more general behaviors ModelSizeResolutionToonX-ToonRatio Mech part10,000 20,000 640x480 1280x950 287 268 241 222 1.19 1.21 David26,051 49,998 640x480 1280x950 94 90 80 76 1.18 Terrain105,152 208,962 640x480 1280x950 33 32 28 27 1.18 1.19

26. Future Work Extend to handle other attributes Use optical flow to assign less detail to objects as they move faster in image space Multiple interpolation weights (geometric mapping) Haloing Labeled importance Points of interest

27. Future Work Geometric mapping → multiple shapes Control the shape of highlights Tech. Rep. 2005 Multiscale Line Drawings from 3D Meshes IEEE Comput. Graph. 2003 Stylized Highlights for Cartoon Rendering and Animation