measurement and editing of metallic car paint brdf martin rump computer graphics group university of...
DESCRIPTION
CESCG 3 Motivation Measurement costly Sometimes only nice images interesting Design process: want to try different paints MeasuredNew EditingTRANSCRIPT
![Page 1: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/1.jpg)
Measurement and editing of metallic car paint BRDF
Martin Rump
Computer Graphics GroupUniversity of Bonn, Germany
![Page 2: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/2.jpg)
224.04.2008 CESCG
Outline• Motivation• Car paint composition and resulting visual effects• Previous work• Our approach• Results
![Page 3: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/3.jpg)
324.04.2008 CESCG
Motivation• Measurement costly• Sometimes only nice images interesting• Design process: want to try different paints
Measured New
Editing
![Page 4: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/4.jpg)
424.04.2008 CESCG
Outline• Motivation• Car paint composition and resulting visual effects• Previous work• Our approach• Results
![Page 5: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/5.jpg)
524.04.2008 CESCG
Pearlescent/flip-flop paintSimple paintMetallic paintCar Paint Composition
Substrat
Electro-coat
Primersurfacer
Finish
Base paint
Color pigments (30-100 nm)Al-Flakes (10-50 μm)
Binder
Car
CoatingDirection dependentcolor shift
GlitteringBase color
![Page 6: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/6.jpg)
624.04.2008 CESCG
Outline• Motivation• Car paint composition and resulting visual effects• Previous work• Our approach• Results
![Page 7: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/7.jpg)
724.04.2008 CESCG
Previous Work (Simulation)• Ershov et al. „Rendering
Pearlescent Appearance Based On Paint-Composition Modelling“ (2001)– Multilayer model– Calculate operators for
sublayers– Combine operators → BRDF– Choose colors for componentsLimitations:
• many parameters• no guarantee for physical
correctness
![Page 8: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/8.jpg)
824.04.2008 CESCG
Previous Work (Measurement)• Günther et al. „Efficient
Acquisition and Realistic Rendering of Car Paint“ (2005)– BRDF measurement– Cook-Torrance model– Realtime raytracing– Editing by changing CT-
parameters
Limitations:- cannot model all colors flops- no flakes
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924.04.2008 CESCG
Previous Work (Measurement)• Matusik et al. „Efficient Isotropic BRDF
Measurement“ (2003)• Matusik et al. „A Data-Driven Reflectance Model“
(2003)Limitations:- no physical correctness- no flakes
![Page 10: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/10.jpg)
1024.04.2008 CESCG
Previous Work (Measurement)• Bidirectional Texture Function (BTF)
Limitation: no straightforward editing possible
![Page 11: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/11.jpg)
1124.04.2008 CESCG
Summary• Simulation of layers:
– Too many (unknown) parameters– No flakes
• BRDF measurement and fitting:– „simple“ Cook-Torrance cannot model all effects– No flakes
• BTF rendering:– Representation not suitable for editing
![Page 12: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/12.jpg)
1224.04.2008 CESCG
Outline• Motivation• Car paint composition and resulting visual effects• Previous work• Our approach• Results
![Page 13: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/13.jpg)
1324.04.2008 CESCG
Hybrid approach
BTF Flake BTFBRDF
+=
BRDF
=
• Image-based representation of sparkles
• Model-based reflection with direction dependent colors
Intensity BRDF Direction dependent color
![Page 14: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/14.jpg)
1424.04.2008 CESCG
• Split color + intensity• Store color in direction dependent table
– Low-frequent → coarse sampling sufficient– 200KB table– No restriction to mechanism of color shift
Our BRDF model
• Basic model: ( , ) , ( , ) ( , )base glossV L I V L V L I V L
Cook-Torrance modelfor intensity
Direction dependent color
table
Colorless reflectionof finish
Sphere painted with color table
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1524.04.2008 CESCG
Separation of BTF• Split BRDF and BTF part• Take light/view direction for every single pixel• Subtract fitted BRDF model• Synthesize BTF part
- =
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1624.04.2008 CESCG
Rendering• Add together BRDF + synthesised BTF
• Path Tracing (mentalray)– High quality– Tonemapping: Use responsecurve from camera
• GPU shader (cgFX, nVidia 8800 GTX)– Only simple and few light sources– Environment mapping– Tonemapping: Reinhard et al. (2005)
),),((,,, LVxsynthBTFLVLVxtotal
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1724.04.2008 CESCG
• Exchange color table
• Exchange flake BTF
Editing (1)
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1824.04.2008 CESCG
• Affine mapping of color plane– Drag, scale, rotate points projected onto
plane– Preview color flop on sphere
Editing (2)
Mx+t
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1924.04.2008 CESCG
Editing (3)
DEMO
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2024.04.2008 CESCG
Outline• Motivation• Car paint composition and resulting visual effects• Previous work• Our approach• Results
![Page 21: Measurement and editing of metallic car paint BRDF Martin Rump Computer Graphics Group University of Bonn, Germany](https://reader036.vdocuments.mx/reader036/viewer/2022081513/5a4d1b267f8b9ab059997250/html5/thumbnails/21.jpg)
2124.04.2008 CESCG
Results (path tracing)• Painted sphere (BRDF only)• Painted sphere (BRDF+BTF)
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2224.04.2008 CESCG
Result: Color edited
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2324.04.2008 CESCG
Result: Color edited
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2424.04.2008 CESCG
Result: Color+flakes changed
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2524.04.2008 CESCG
Conclusion• Hybrid rendering approach combining BRDF + BTF• Direction dependent color table for arbitrary color
shift• Editing by affine transformation of color table
– Transformation in shader possible• Editing by exchange of flake BTF
Questions?