60 June 22 nd Antoine LUCAT Problematic How to qualify a BRDF - - PowerPoint PPT Presentation

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60 June 22 nd Antoine LUCAT Problematic How to qualify a BRDF - - PowerPoint PPT Presentation

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R. Hegedus and A. Lucat and J. Redon and R. Pacanowski 60 June 22 nd Antoine LUCAT Problematic How to qualify a BRDF measurement ? Graphics Photo vs. Rendering Qualitative error June 22 nd Antoine LUCAT 1 Problematic How to

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June 22nd Antoine LUCAT

  • R. Hegedus and A. Lucat and J. Redon and R. Pacanowski

60°

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June 22nd Antoine LUCAT

Problematic

 How to qualify a BRDF measurement ?

Graphics Photo vs. Rendering

1

Qualitative error

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June 22nd Antoine LUCAT

Problematic

 How to qualify a BRDF measurement ?

Graphics Two setups = two different BRDFs [Obein15]

1

Photo vs. Rendering Qualitative error

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June 22nd Antoine LUCAT

Problematic

 How to qualify a BRDF measurement ?

Graphics Optics

1

Photo vs. Rendering Quantitative error Qualitative error 30°

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June 22nd Antoine LUCAT

Problematic

 How to qualify a BRDF measurement ?

Optics Aim:

  • Create a database with

quantified uncertainties

  • Material characterization

1

Quantitative error 30°

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June 22nd Antoine LUCAT

The Setup

Inspired by [Matusik03] and [Marschner99]

2

Camera Light Sphere

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June 22nd Antoine LUCAT

The Setup

2

→1 BRDF configuration : 1 pixel + 1 rotation →Isotropic BRDF only Inspired by [Matusik03] and [Marschner99] Camera Sphere Light

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June 22nd Antoine LUCAT

Measurement Principle

Raw image Real setup

3

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June 22nd Antoine LUCAT

Measurement Principle

Virtual setup

3

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June 22nd Antoine LUCAT

Measurement Principle

Measured BRDF

Reconstruction

3 Raytracing

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June 22nd Antoine LUCAT

Uncertainties Propagation

? Initial error Final error

4

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June 22nd Antoine LUCAT

Uncertainties Propagation

Initial error Final error No correlation Perfect correlation

4

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June 22nd Antoine LUCAT

Uncertainties Propagation

Initial error Final error No correlation Perfect correlation

4

Initial error

+error +error +error +error

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June 22nd Antoine LUCAT

Uncertainties Propagation

Initial error Final error No correlation Perfect correlation

4

+error +error +error +error

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June 22nd Antoine LUCAT

Results

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June 22nd Antoine LUCAT

Data & Resolution

Specular Mirror Copper Teflon Spectralon

5

Lambert. Standart

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June 22nd Antoine LUCAT

Data & Resolution

Lambert. Standart Specular Mirror Copper Teflon Spectralon 30° 60°

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June 22nd Antoine LUCAT

Data & Resolution

Specular Mirror Copper Teflon Spectralon

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Lambert. Standart Position uncertainty Value uncertainty

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June 22nd Antoine LUCAT

Data & Resolution

Specular Mirror Copper Teflon Spectralon

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Uncertainty model results :

Angular resolution : 0.1° → 12° (normal to grazing view angle) Value uncertainty : 3% → 100% Range ( , , ) : (0-85°, 0-90°, 0-360°) ~100 000 000 points for 1° rotation step Lambert. Standart

%

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June 22nd Antoine LUCAT

Uncertainty Analysis

View elevation Light elevation Azimuthal angle

6

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June 22nd Antoine LUCAT

Uncertainty Analysis

View elevation Light elevation Azimuthal angle

6

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June 22nd Antoine LUCAT

Uncertainty Analysis

View elevation Light elevation Azimuthal angle

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= 0

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June 22nd Antoine LUCAT

Uncertainty Analysis

View elevation Light elevation Azimuthal angle

Light independent

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= 0

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June 22nd Antoine LUCAT

Uncertainty Analysis

= 0 = 0 = 0 = 0 = 0

View elevation Light elevation Azimuthal angle

Light independent

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June 22nd Antoine LUCAT

Uncertainty Analysis

 Unreliable grazing angle measurements

→3 orders of magnitude

= 0 = 0 = 0 = 0 = 0 Light independent

6

103

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June 22nd Antoine LUCAT

Uncertainty Analysis

 Unreliable grazing angle measurements

→3 orders of magnitude

 Main source of error :

→focal and light uncertainties

= 0 = 0 = 0 = 0 = 0 Light independent

6

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Future Work

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June 22nd Antoine LUCAT

Issues and Future Work

 Non-uniformities :

− White light speckle

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June 22nd Antoine LUCAT

Issues and Future Work

 Non-uniformities :

− White light speckle

7

Without roughness

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June 22nd Antoine LUCAT

Issues and Future Work

 Non-uniformities :

− White light speckle

7

with roughness

→Surface diffraction

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June 22nd Antoine LUCAT

Issues and Future Work

 Non-uniformities :

− White light speckle − Light field

8

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June 22nd Antoine LUCAT

Issues and Future Work

 Non-uniformities :

− White light speckle − Light field

Light stains

Beam intensity

8

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June 22nd Antoine LUCAT

Issues and Future Work

 Non-uniformities :

− White light speckle − Light field

 Convolution :

− Aperture diffraction →Lens diffraction

9

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June 22nd Antoine LUCAT

Issues and Future Work

 Non-uniformities :

− White light speckle − Light field

 Convolution :

− Aperture diffraction →Lens diffraction

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time of exposure f-number dynamic range DOF aberrations T r a d e

  • f

f

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June 22nd Antoine LUCAT

Conclusion

 BRDF measurement with quantified

uncertainties

 Absolute definition of the setup's quality of

measurement

 Possible comparison between different

setups

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June 22nd Antoine LUCAT

Thank you for your attention

Data will be released on ALTA: http://alta.gforge.inria.fr/data.html

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June 22nd Antoine LUCAT

Reference

[Matusik03]

Matusik W., Pfister H., Brand M., McMillan L. : Efficient isotropic BDRF measurement. In Proc. EGWR '03 (2003), pp. 241-247.

[Marschner98]

Marschner S.R., Westin S.H., Lafortune E.P.F., Torrance K.E., Greenberg D.P.: Image-Based BRDF Measurement Including Human Skin. In Proc. of 10th Eurographics Workshop on Rendering, p.139-152, June 1999.

[Obein15]

Obein G., Audenaert J., Ged G., Leloup F.B. : Metrological issues related to BDRF measurements around the specular direction in the particular case of glossy surfaces. In Proc. SPIE 9398, Measuring, Modeling, and Reproducing Material Appearance 2015, 93980D (March 13, 2015), doi:10.1117/12.2082518.

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June 22nd Antoine LUCAT

Supplemental

 Depth-of-field ?  Other results ?  Formulas ?  Order of errors by parameters (11) ?  Videos ?