CrossShade: Shading Concept Sketches Using Cross-section Curves Presenter: Feilong Yan

Introduction Sketch Shaded Sketch: Production drawing

Introduction Sketch Manually 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 field Production 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 Estimation Assumption : Orthographic projection Orthogonality: Local Geodesics &Minimal Foreshorening: Inherent Constrained: At each cross-hair, the intersecting 3D curves share the same depth z:

Normal Propagation Propagate the normals of the cross-hairs along the cross-section curves Interpolate all the sketch

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 shading Sketch

Thank You