３Ｄ physics-based brush model for painting Tokyo Institute of Technology Suguru Saito, Masayuki Nakajima Tokyo Institute of Technology Suguru Saito, Masayuki Nakajima

Contents Background Related work Purpose Explanation of our brush model Experiment & Painting result Conclusion & Future work Background Related work Purpose Explanation of our brush model Experiment & Painting result Conclusion & Future work

Background Picasso Musashi Miyamoto

Background Expressive strokes are important strong, sharp, soft, smoothstrong, sharp, soft, smooth Real brushes can answer feelings of painters Expressive strokes are important strong, sharp, soft, smoothstrong, sharp, soft, smooth Real brushes can answer feelings of painters

Background Limit of stroke shape by disc base method

Major drawing technique Disc based methods Disc based methods merit of calculationmerit of calculation –fast, easy algorithm limit of Stroke shapelimit of Stroke shape –Turning point, finishing point Major drawing technique Disc based methods Disc based methods merit of calculationmerit of calculation –fast, easy algorithm limit of Stroke shapelimit of Stroke shape –Turning point, finishing point Background

Related Work For input of variety and expressive strokes fatten center curve algorithmfatten center curve algorithm –Strassmann et.al.[1986] –limit of stroke shape texture mapping based algorithmtexture mapping based algorithm –Hus et.al.[1994] –different input style to real brush For input of variety and expressive strokes fatten center curve algorithmfatten center curve algorithm –Strassmann et.al.[1986] –limit of stroke shape texture mapping based algorithmtexture mapping based algorithm –Hus et.al.[1994] –different input style to real brush

Related Work For input of variety and expressive strokes physics-based brush modelphysics-based brush model –Lee[1999] –tuft’s footprint becomes a line segment… For input of variety and expressive strokes physics-based brush modelphysics-based brush model –Lee[1999] –tuft’s footprint becomes a line segment…

Purpose Is to propose a new input technique for interactive painting 1) allows to draw expressive strokes 2) enables intuitive and direct operation Is to propose a new input technique for interactive painting 1) allows to draw expressive strokes 2) enables intuitive and direct operation

Purpose For 1) Three dimensionalThree dimensional physics-based tuft model physics-based tuft model For 2) Use of a pen tablet deviceUse of a pen tablet device For 1) Three dimensionalThree dimensional physics-based tuft model physics-based tuft model For 2) Use of a pen tablet deviceUse of a pen tablet device

Proposed brush model Physical modelingPhysical modeling Spine curve & FootprintSpine curve & Footprint Liquid movementLiquid movement Physical modelingPhysical modeling Spine curve & FootprintSpine curve & Footprint Liquid movementLiquid movement

Simple structure Physical modeling Solve the joint’s angle for the minimum system energy Bending energy of the jointBending energy of the joint kinetic energy of the masskinetic energy of the mass potential energy of the masspotential energy of the mass frictional energyfrictional energy Posture and Position Newton-Raphson technique

Proposed brush model Physical modelingPhysical modeling Spine curve & FootprintSpine curve & Footprint Liquid movementLiquid movement Physical modelingPhysical modeling Spine curve & FootprintSpine curve & Footprint Liquid movementLiquid movement

A spine curve is defined as Bezier curve by 3 control points Spine curve & Footprint Then the footprint is derived

Proposed brush model Physical modelingPhysical modeling Spine curve & FootprintSpine curve & Footprint Liquid movementLiquid movement Physical modelingPhysical modeling Spine curve & FootprintSpine curve & Footprint Liquid movementLiquid movement

Virtual structure Virtual structure Liquid movement Calculation of movement direction in pipe from Gravity to liquidGravity to liquid absorption force from paperabsorption force from paper absorption force from the tuftabsorption force from the tuft

Experiment The relation between the handle posture and the spine curve easy control by the handle motion The relation between the handle posture and the spine curve easy control by the handle motion

Experiment Changing footprint shape Natural response to the handle posture Dynamic drip shapes Changing footprint shape Natural response to the handle posture Dynamic drip shapes

System Hardware: Pentium 450MHz OS: Linux Graphics system: X window system Graphic library: gtk+ Input device: wacom pen tablet Hardware: Pentium 450MHz OS: Linux Graphics system: X window system Graphic library: gtk+ Input device: wacom pen tablet

Additional model information for paint tool Paint model: based on Kubelka-Munk theory => color calculation by => color calculation by –paint density, layer thickness =>easy color mixture =>easy color mixture Paper model: cell array cell size = pixel size cell size = pixel size cell’s paint capacity: defined by scanned paper texture cell’s paint capacity: defined by scanned paper texture Paint model: based on Kubelka-Munk theory => color calculation by => color calculation by –paint density, layer thickness =>easy color mixture =>easy color mixture Paper model: cell array cell size = pixel size cell size = pixel size cell’s paint capacity: defined by scanned paper texture cell’s paint capacity: defined by scanned paper texture

Painting results Japanese character “kana” Characteristic drawing at Finishing point,Turning point expression of user’s peculiarity

Painting results A Japanese character ‘kanji’ Tao

Painting results A Japanese style picture 4 strokes’ painting

Painting results A Japanese style picture flowers

Conclusion A new brush model is proposed 3D physics-based brush model highly expressive strokehighly expressive stroke –dynamic change of footprint shape –subtlety gradation by paint liquid quantity interactiveinteractive –direct and intuitive operation –natural manner similar to real painting A new brush model is proposed 3D physics-based brush model highly expressive strokehighly expressive stroke –dynamic change of footprint shape –subtlety gradation by paint liquid quantity interactiveinteractive –direct and intuitive operation –natural manner similar to real painting

Future work More complex liquid movement –scratch stroke, blotting stroke Visualization of paint quantity in brush Improvement of the transformation pressure to ‘z’ value Complete paint tool More complex liquid movement –scratch stroke, blotting stroke Visualization of paint quantity in brush Improvement of the transformation pressure to ‘z’ value Complete paint tool