CrossShade: Shading Concept Sketches Using Cross-section Curves Presenter: Feilong Yan
Jan 16, 2016
CrossShade:Shading Concept Sketches Using
Cross-section Curves
Presenter: Feilong Yan
Introduction
SketchShaded Sketch:Production drawing
Introduction
SketchManually shading
• Manually shade with painting tools• Convert sketch to complete 3D Model
Introduction
• A natural question is “Is there a better way ?”• Fast & reusable
This Paper
• This paper facilitates the creation of 3D-looking shaded production drawing from sketches by the normal field estimated from cross section curves.
Sketch Normal fieldProduction drawing
Main Work & Contribution
• 1. An explicit mathematical formulation of the relationship between sketched cross-section curves and the 3D geometry they aim to convey
Main Work & Contribution
• 2. An algorithm for extracting a normal field from cross-section curve networks based on the formulation above.
Cross Section & Cross Hair
Formulation
1. Orthogonal Cross-Hair Planes:Perception studies indicate that designer consistently use orthogonal planes for intersecting cross-sections.
Formulation
2. Cross-Sections as Curvature Lines:Perception studies indicate that observers interpret intersecting curves as aligned with the principal lines of curvature.
Formulation
3. Cross-sections as Local Geodesics:
4. Minimal Foreshortening :
5. Orientation:
Human perceive intersecting cross-section curves as geodesics
When drawing a shape, designers favor informative viewpoints that convey most visible surface with minimal foreshortening
Geometry Estimation
• Cross-Section Plane Estimation : Use energy function constrained by 5 Formulations at the cross hair to
estimate the support plane of cross-section curves • Normal Propagation: curve normal estimation -> patch construction-> Coons interpolation
Cross-Section Plane EstimationAssumption : Orthographic projection
Orthogonality:)2(
)1(
jiij
ji
tt
nn
Local Geodesics &Minimal Foreshorening:
)3()()()(min 2222 zji
zijiji
ijiji
nttntnt
i
Inherent Constrained:
)4(0 iij nt
At each cross-hair, the intersecting 3D curves share the same depth z:
)5(0,0 jjii cnxcnx
Normal Propagation
• Propagate the normals of the cross-hairs along the cross-section curves
• Interpolate all the sketch
Result
Result
Result
Not a Conclusion
• While the automatic shading quality can never match the expressiveness of manual artwork, the result are aspired , and can express the major features in the production drawing.
Manually shading Automatic shadingSketch
Thank You