Binary Shading using Geometry and Appearance Bert Buchholz Tamy Boubekeur Doug DeCarlo Marc Alexa Telecom ParisTech – CNRS Rutgers University TU Berlin Computer Graphics Forum Vol. 29, N. 6, 2010 Presented at Eurographics 2011

Binary Drawing Depicting scenes using 2 colors

Conversion Binary Rendering Lighting Reflectance Geometry Camera

Related Work Line Drawing [DeCarlo 2003][Judd 2007] Image Binarization [Mould and Kaplan 2008] Local shading operators [Vergne 2008] Half-Toning [Floyd and Steinberg 1976] [Ostromoukhov and Hersch 1995]

Analysis Variational Rendering Model Per-pixel decision Contradictory criteria Geometry enhancement Low shading depiction power

VARIATIONAL BINARY RENDERING

Variational Binary Shading Deferred shading framework Rendering data structured as a ST image graph Edges energies derived from geometry and appearance Final rendering as a min cut in the image graph

Deferred Shading Generate a set of arrays (render buffers) – Geometric Properties – Appearance Properties Rasterization Ray Tracing

Graph construction Standard Source-to-Sink Image Graph {V,E} Image Pixels Source (white) Sink (black) Image Connectivity Edges to Source Edges to SInk

Appearance Contribution to the Graph Through terminal weights on Appearance initiate B/W segmentation Experiments using : – Diffuse component – Specular component – Headlight component – Ambient Occlusion/Accessibility component Terminal Weights

Appearance Graph Terms Global to local feature control using spatial averages Support size Local term: Sign:locally lighter or darker Weighted combination to the global measure.

Global versus Local Thresholding GlobalLocal

Geometry Contribution to the Graph Modelled with neighbor edge weights Tailors anisotropic, non-local B/W diffusion Redistributes B/W values to enhance geometric features Based on: – View depth values – View dependent curvature, estimated as screen space normal derivatives [Judd 2007] Geodesic distance on the Gauss sphere Unit surface normal gathered at

Geometric Term Local curvature normalization: Support size Yields neighbor edge weights:

Geometry Contribution Modulation

Small components are successively connected

Graph Minimum Cut Max Flow Min Cut Theorem – Shortest split path in the graph →Feature size control through graph energy Separate the graph in two components Boykov and Kolmogorov implementation [2004]

Cut performance Rendering buffers can be speed up using rasterization Measured on a Core2Duo 1.83GHz (single thread)

RESULTS

Binary Shading Global to local features Appearance & geometry depiction Large variety of style Interactive control

Comparison to Line Drawing Line Drawing Binary Shading

Combination with Line Drawing

RGBN Picture Rendering [Toler-Franklin 2007]

Combination with Line Drawing

Comparison to Thresholding Diffuse Component Thresholding Over Gaussian Filtering Binary Rendering

Comparison to Thresholding

Comparison to Image Binarization (b,e) equivalent to [Mould and Kaplan 2008]

INTERACTIVE CONTROL On-going work

Interactive Control Solution 1: slider-based, for experts – Accurate control – « Too much » control for novice users Solution 2: painting interface

Paint Interface Supervised sparse B/W contraints Derive the graph energy structure

Paint Interface

LIMITATIONS AND FUTURE WORK

Animation … most of straightforward solutions have some temporal coherency failure cases. Works most of the time but…

K-color Rendering Extend to multi-label cuts Alternative energy minimizer – Lloyd relaxation/k-means – Mean Shift k-Component cut Vector Rendering

CONCLUSION

Binary Shading as a Single Cut Global solution Local to global control Appearance vs geometry control High level control For automatic binary drawing from 3D Scenes, decals, cut-out, etc…

Thank you Binary Shading Using Geometry and Appearance. Bert Buchholz, Tamy Boubekeur, Doug DeCarlo and Marc Alexa Computer Graphics Forum Vol. 29, Nb. 6, 2010 Presented at Eurographics 2011