Odrazivost a rozptyl světla
- Jiří Filip · ÚTIA AV ČR · ANI-PG2
- Parametrizace a zachycení materiálů pomocí BRDF a BSSRDF.
- Export PDF: 30. 9. 2026. Aktuální termín výuky není v rozcestníku uveden.
Původní snímek · 1
BRDF measurement
- Sample the reflectance lobe rather than only a convenient set of directions.
- Measurement balances acquisition speed and fidelity.
- Uniform versus adaptive sampling, angular parameterization and the mechanical degrees of freedom of the capture device are linked.
Původní snímek · 2
Isotropic and anisotropic BRDF
- BRDF: Bidirectional Reflectance Distribution Function.
- Reflectance depends on illumination and viewing directions.
- For an isotropic material, a common rotation around the normal does not change reflectance; the relative azimuth matters.
- Anisotropic materials retain orientation-dependent highlights.
Původní snímek · 3
Anisotropic BRDF: unfolding 4D data
- Four angular coordinates: incident and viewing polar/azimuth angles.
- The author unfolds the angular domain into a 2D visualization.
- Compare a specular highlight with anisotropic highlights across the slices.
Původní snímek · 4
Angular parameterizations
- Illumination–view angles directly describe the light and camera directions.
- Half–difference angles: Rusinkiewicz (1998).
- Onion-slices model: Havran et al.; compare spatially uniform and angularly uniform sampling in the original diagrams.
Původní snímek · 5
Half–difference parameterization
- The half vector describes the orientation halfway between illumination and view.
- The source distinguishes specular-peak, anisotropy, Fresnel-peak, reciprocity and symmetry behaviour.
- Burley’s characteristic slice is illustrated with a capture using 108 samples.
Původní snímek · 6
Characteristic slices and symmetry
- Reparameterize fᵣ(θᵢ, φᵢ, θᵥ, φᵥ) using half and difference angles.
- Isotropic behaviour removes dependence on the common half-vector azimuth.
- The author illustrates reciprocity, bilateral symmetry and bivariate BRDF slices (Rusinkiewicz 1998; Burley 2012).
Původní snímek · 7
Comparing angular parameterizations
- Hemispherically uniform sampling versus bivariate sampling of effect coatings.
- Compare the source photographs: a different angular grid can capture or miss important appearance changes.
Původní snímek · 8
Uniform and adaptive sampling
- The source compares axial and diagonal BRDF slices.
- Adaptive sampling may operate on the 4D function or along 1D functions embedded in that space.
- The cited CVPR 2013 method uses cross-validation error at control samples.
- The GRAFIT example below is a separate synthetic 1D illustration, not that measurement method.
Původní snímek · 9
BRDF measurement setups: taxonomy
- Gonio-reflectometers, mirror-based setups, image-based setups and portable setups.
- Mechanical positioning may distribute four angular degrees of freedom among the sample, light and camera.
- The source’s 5D/4D data labels include spectral dependence; at a fixed wavelength the anisotropic angular domain is 4D (isotropic: 3D).
- Capture accuracy and practical portability involve different compromises.
Původní snímek · 10
Gonio-reflectometers
- Sequential sampling moves the sample, light and camera through the angular domain.
- The source shows Murray & Smith (1990) and White et al. (1998).
Původní snímek · 11
Spectral and adaptive gonio-reflectometry
- Spectral isotropic/anisotropic BRDF measurement.
- Dupuy et al. (2018): adaptive sample parameterization; compare the device and sampling diagrams.
Původní snímek · 12
Mirror-based setups: directional illumination
- Multiple views in a mirror image reduce mechanical degrees of freedom.
- The author compares Ward (1992) and Dana et al. (2001).
Původní snímek · 13
Mirror-based setups: projected illumination
- Projected illumination patterns provide another route to reducing mechanical motion.
- Source examples: Mukaigawa et al. (2007) and Ghosh et al. (2007).
Původní snímek · 14
Ellipsoidal-reflector prototype
- Filip (CIE 2016): ellipsoidal reflector, AAXA P300 projector (300 lm), Sony H1 camera.
- Camera–reflector distance: 1.5 m. A lens close to the projector window gives nearly identical optical paths.
- Calibrate the light–camera–reflector alignment using a projected pattern.
- The reported measurement time is 1–3 minutes for this source setup.
Původní snímek · 15
Measured and reference appearances
- The author compares measured results and reference photographs for several materials.
- Inspect highlight shape and structure across rows and columns in the original illustration.
Původní snímek · 16
Image-based setups: known shape
- A defined sample shape constrains surface orientation and reduces required mechanical motion.
- A cylinder image contains varying incoming/outgoing directions (Lu et al. 1998).
- Other examples use estimated geometry (Marschner et al. 2000; Ngan et al. 2005).
Původní snímek · 17
Image-based setups: spheres
- Spherical, homogeneous samples expose many orientations in an image.
- The source compares Marschner (1998) and Matusik et al. (2003).
Původní snímek · 18
Image-based setups: a large sample
- Varying angles across a large material sample (Filip, ICPR 2014).
- The source describes a 30 cm sample and an angular resolution of 2°.
- Sampling spots and capture geometry are shown in the diagram.
Původní snímek · 19
Portable setups
- Faster and more portable capture compromises angular coverage and accuracy.
- Important limits: the number of illumination/sensing elements and the range of viewing/illumination angles.
- Source examples: Ben-Ezra et al. (2008) and Lan et al. (2010).
Původní snímek · 20
BSSRDF: subsurface light transport
- Bidirectional subsurface-scattering reflectance distribution function (Nicodemus et al. 1977).
- Scattering transports light between distinct incident and outgoing positions and directions.
- The source describes general 9D data / reflectance fields and sparse direct measurement due to dimensionality.
- BTF includes scattering effects, but separating them is difficult.
Původní snímek · 21
Measuring spatially varying scattering
- Goesele et al. (2004): sparse laser-based subsurface-scattering measurements.
- Tong et al. (2005): BTF combined with local laser measurements.
- Compare BTF alone, BTF with local scattering, and BTF with global scattering.
Původní snímek · 22
Fitting scattering models
- Homogeneous dielectric materials can be described by subsurface-scattering models.
- Jensen et al. (2001): a dipole model validated with a focused beam.
- Separate diffuse and specular components using polarization, colour or illumination patterns; the diffuse component supports fitting scattering parameters.
- Source references include Shafer (1985) and Nayar et al. (1997, 2006).
Původní snímek · 23
Volumetric model acquisition
- Zhao et al. (2011): micro-CT geometry combined with optical scattering information fitted to sample photographs.
- Benefit: realistic material appearance.
- Limits in the source: one assumed material, lengthy rendering and the scanner’s limited dynamic range.
- The resolution notation in the PDF is retained in its original illustration rather than guessed from damaged text extraction.
Původní snímek · 24
Practical BRDF measurement examples
- Highly specular materials.
- Extremely dark materials.
- Translucency.
Původní snímek · 25
Specular materials: capture strategy
- Green paint with a thick acrylic coating and silver 925 (92.5% silver, 7.5% copper).
- BRDF is obtained by averaging BTF images from the UTIA goniometer.
- Half–difference parameterization and nonlinear angular sampling; the source describes 108 images/samples.
- Measured area: 3 × 3 mm. Shape courtesy of Lechler S.p.a., Como, Italy.
Původní snímek · 26
Specular materials: anisotropic artefacts
- Insufficient polishing creates scratches and unwanted anisotropy.
- Highlights appear perpendicular to the scratches.
- The author discusses choosing a suitable angular slice and warns against treating MERL examples as an unquestioned reference.
Původní snímek · 27
Specular materials: aperture diffraction
- Light passing through a narrow aperture produces diffraction streaks.
- Bright streaks are perpendicular to aperture blades; an odd blade count produces twice as many streaks in the illustrated situation.
- The effect is pronounced with a small aperture and bright point light. The author proposes a circular aperture.
Původní snímek · 28
Specular materials: flare and environment
- Lens flare arises from internal reflections; the source notes stronger effects with more lens elements and suppression using a long lens hood.
- Mirror-like finishes reflect the measurement environment.
- The source proposes diffuse black covering to suppress unwanted environmental reflections.
Původní snímek · 29
Specular materials: rendered comparison
- Compare the appearance of highly reflective objects and their reflected environments.
- The original slide points to Cem Yuksel’s Interactive Graphics Course; the original PDF link is preserved where present.
Původní snímek · 30
Extremely dark BRDFs: motivation
- Black materials support stray-light suppression, calibration and imaging.
- Materials that look similar under diffuse light can differ strongly under directional illumination.
- VACNT ultra-black materials are costly and fragile.
- The author motivates comparing alternative solutions by cost and performance.
Původní snímek · 31
Extremely dark BRDFs: materials and costs
Původní ceny a parametry patří k podkladu; nejde o současnou nabídku.
- The source compares VACNT Vantablack, Musou Black, acrylic spray paint, chalkboard paint, black velvet and Musou fabric.
- Original price, quantity and sample-area figures remain available in the source illustration and selectable source text.
- These are figures from the lecture material, not current prices or purchasing advice.
Původní snímek · 32
Extremely dark BRDFs: acquisition
- UTIA high-precision goniometer; RGB camera and visible-spectrum measurements.
- 24,488 samples per material. Long exposures for black materials led to a reported 96-hour acquisition.
- Suppress and compensate stray light.
Původní snímek · 33
Dark materials: angular data
- The original panel compares measured responses across several black materials.
- Inspect the angular patterns rather than judging darkness from one photograph.
Původní snímek · 34
Dark materials: illumination conditions
- Compare reflections under HDR/high-intensity and low-intensity imaging conditions.
- Coatings and fabrics can behave differently under directional illumination.
- Use the labelled source panels to identify material and acquisition conditions.
Původní snímek · 35
Dark materials: integrated quantities
- Total hemispherical reflectance: integrate fᵣ(ωᵢ, ωᵥ) cos θᵥ over outgoing solid angle.
- Albedo in the source: integrate ρ(ωᵢ) cos θᵢ over incident directions.
- Total integrated scatter: TIS = Rᵈ / Rᵗ = Rᵈ / (Rˢ + Rᵈ).
- The author’s original integral notation and geometry are preserved alongside the HTML explanation.
Původní snímek · 36
Dark materials: comparing metrics
- Compare the source plots of angular and integrated measurements across the material samples.
- Darkness and scattering distribution answer different questions.
- The measured curves are original author data; the sampling model in this web is a separate synthetic example.
Původní snímek · 37
Translucency of printing filaments
- 17 filament samples of diameter 1.7 mm.
- 15 PLA samples; PET samples 13 and 17.
- The source photograph identifies the coloured specimens.
Původní snímek · 38
Translucency: capture arrangement
- Sighttex Q material-appearance capture device.
- 3,660 BRDF values: 61 × 60 illumination/view directions.
- Measure a small spot on each filament against both white and dark backgrounds.
Původní snímek · 39
Translucency: filtering and background difference
- Filter raw BRDF data using light/view reciprocity and isotropy.
- The source illustrates BRDFs against a white background and a translucency proxy from the white–dark difference.
- Keep the background and filtering assumptions visible when interpreting the difference.
Původní snímek · 40
Translucency: appearance renderings
- Compare the original BRDF renderings against dark and white backgrounds.
- The source panel shows how the same filament samples change under the two capture conditions.
Původní snímek · 41
References: BRDF measurement I
References
BRDF measurement
•
Murray-Coleman, J., Smith, A.: The automated measurement of BRDFs and
their application to luminaire modeling. Journal of the Illuminating
Engineering Society pp. 87–99 (1990)
•
White, D.R., Saunders, P., Bonsey, S.J., van de Ven, J., Edgar, H.:
Reflectometer for measuring the bidirectional reflectance of rough surfaces.
Journal of Applied Optics 37, 3450–3454 (1998)
•
Ward, G.: Measuring and modeling anisotropic reflection. Computer
Graphics 26(2) (1992)
•
Dana, K.: BRDF/BTF measurement device. ICCV 2001, vol. 2, pp. 460–466
(2001)
•
Mukaigawa, Y., Sumino, K., Yagi, Y.: Multiplexed illumination for measuring
BRDF using an ellipsoidal mirror and a projector, ACCV’07, pp. 246–257
•
Ghosh, A., Achutha, S., Heidrich, W., O’Toole, M.: BRDF acquisition with
basis illumination. ICCV 2007, 1–8 (2007)
BRDF measurement
•
Murray-Coleman, J., Smith, A.: The automated measurement of BRDFs and
their application to luminaire modeling. Journal of the Illuminating
Engineering Society pp. 87–99 (1990)
•
White, D.R., Saunders, P., Bonsey, S.J., van de Ven, J., Edgar, H.:
Reflectometer for measuring the bidirectional reflectance of rough surfaces.
Journal of Applied Optics 37, 3450–3454 (1998)
•
Ward, G.: Measuring and modeling anisotropic reflection. Computer
Graphics 26(2) (1992)
•
Dana, K.: BRDF/BTF measurement device. ICCV 2001, vol. 2, pp. 460–466
(2001)
•
Mukaigawa, Y., Sumino, K., Yagi, Y.: Multiplexed illumination for measuring
BRDF using an ellipsoidal mirror and a projector, ACCV’07, pp. 246–257
•
Ghosh, A., Achutha, S., Heidrich, W., O’Toole, M.: BRDF acquisition with
basis illumination. ICCV 2007, 1–8 (2007)
Původní snímek · 42
References: BRDF measurement II
References
BRDF measurement
•
Lu, R., Koenderink, J.J., Kappers, A.M.L.: Optical properties (bidirectional
reflectance distribution functions) of velvet. Applied Optics 37, 5974 5984
(1998)
•
Ngan, A., Durand, F., Matusik, W.: Experimental analysis of BRDF models.
Eurographics Symposium on Rendering 2005 pp. 117–126 (2005)
•
Marschner, S.R., Westin, S.H., Lafortune, E.P.F., Torrance, K.E.: Image-based
biderectional reflectance distribution function measurement. Applied Optics
39 (2000)
•
Matusik,W., Pfister H.P. Brand, M., McMillan, L.: Image-based BRDF
measurement including human skin. In: Proceedings of 10th
EurographicsWorkshop on Rendering, pp. 139–152 (2003)
•
Ben-Ezra, M., Wang, J., Wilburn, B., Li, X., Ma, L.: An LED-only BRDF
measurement device. CVPR 2008, 1–8
•
Lan, Y., Dong, Y.,Wang, J., Tong, X., Guo, B.: Condenser-based instant
reflectometry. Computer Graphics Forum 29(7), 2091–2098 (2010)
BRDF measurement
•
Lu, R., Koenderink, J.J., Kappers, A.M.L.: Optical properties (bidirectional
reflectance distribution functions) of velvet. Applied Optics 37, 5974 5984
(1998)
•
Ngan, A., Durand, F., Matusik, W.: Experimental analysis of BRDF models.
Eurographics Symposium on Rendering 2005 pp. 117–126 (2005)
•
Marschner, S.R., Westin, S.H., Lafortune, E.P.F., Torrance, K.E.: Image-based
biderectional reflectance distribution function measurement. Applied Optics
39 (2000)
•
Matusik,W., Pfister H.P. Brand, M., McMillan, L.: Image-based BRDF
measurement including human skin. In: Proceedings of 10th
EurographicsWorkshop on Rendering, pp. 139–152 (2003)
•
Ben-Ezra, M., Wang, J., Wilburn, B., Li, X., Ma, L.: An LED-only BRDF
measurement device. CVPR 2008, 1–8
•
Lan, Y., Dong, Y.,Wang, J., Tong, X., Guo, B.: Condenser-based instant
reflectometry. Computer Graphics Forum 29(7), 2091–2098 (2010)
Původní snímek · 43
References: BSSRDF measurement
References
BSSRDF measurements
•
Nicodemus, F., J.C., R., Hsia, J., Ginsburg, I., Limperis, T.: Geometrical
considerations and nomenclature for reflectance. NBS Monograph 160,
National Bureau of Standards, U.S. Department of Commerce, Washington,
D. C. pp. 1–52 (1977)
•
Goesele, M., Lensch, H.P.A., Lang, J., Fuchs, C., Seidel, H.P.: Disco: acquisition
of translucent objects. ACM Trans. Graph. 23, 835–844 (2004)
•
Tong, X., Wang, J., Lin, S., Guo, B., Shum, H.Y.: Modeling and rendering of
quasihomogeneous materials. In: ACM SIGGRAPH 2005 Papers, SIGGRAPH
’05, pp. 1054–1061. ACM, New York, NY, USA (2005)
•
Jensen, H.W., Marschner, S.R., Levoy, M., Hanrahan, P.: A practical model for
subsurface light transport. In: Proceedings of the 28th annual conference on
Computer graphics and interactive techniques, SIGGRAPH ’01, pp. 511–518.
ACM, New York, NY, USA (2001)
BSSRDF measurements
•
Nicodemus, F., J.C., R., Hsia, J., Ginsburg, I., Limperis, T.: Geometrical
considerations and nomenclature for reflectance. NBS Monograph 160,
National Bureau of Standards, U.S. Department of Commerce, Washington,
D. C. pp. 1–52 (1977)
•
Goesele, M., Lensch, H.P.A., Lang, J., Fuchs, C., Seidel, H.P.: Disco: acquisition
of translucent objects. ACM Trans. Graph. 23, 835–844 (2004)
•
Tong, X., Wang, J., Lin, S., Guo, B., Shum, H.Y.: Modeling and rendering of
quasihomogeneous materials. In: ACM SIGGRAPH 2005 Papers, SIGGRAPH
’05, pp. 1054–1061. ACM, New York, NY, USA (2005)
•
Jensen, H.W., Marschner, S.R., Levoy, M., Hanrahan, P.: A practical model for
subsurface light transport. In: Proceedings of the 28th annual conference on
Computer graphics and interactive techniques, SIGGRAPH ’01, pp. 511–518.
ACM, New York, NY, USA (2001)
Původní snímek · 44
References: component separation and volumes
References
BSSRDF - diffuse/specular components separation
•
Shafer, S.A.: Using color to separate reflection components. Color Research
& Application 10(4), 210–218 (1985)
•
Nayar, S.K., Fang, X.S., Boult, T.: Separation of reflection components using
color and polarization. International Journal of Computer Vision 21, 163–
186 (1997).
•
Nayar, S.K., Krishnan, G., Grossberg, M.D., Raskar, R.: Fast separation of
direct and global components of a scene using high frequency illumination.
ACM Trans. Graph. 25, 935–944 (2006)
Volumetric Model Acquisition
•
S. Zhao,W. Jakob, S. Marschner, K. Bala, Building volumetric appearance
models of fabric using micro CT imaging, ACM Trans. Graph., 30(4), 2011
BSSRDF - diffuse/specular components separation
•
Shafer, S.A.: Using color to separate reflection components. Color Research
& Application 10(4), 210–218 (1985)
•
Nayar, S.K., Fang, X.S., Boult, T.: Separation of reflection components using
color and polarization. International Journal of Computer Vision 21, 163–
186 (1997).
•
Nayar, S.K., Krishnan, G., Grossberg, M.D., Raskar, R.: Fast separation of
direct and global components of a scene using high frequency illumination.
ACM Trans. Graph. 25, 935–944 (2006)
Volumetric Model Acquisition
•
S. Zhao,W. Jakob, S. Marschner, K. Bala, Building volumetric appearance
models of fabric using micro CT imaging, ACM Trans. Graph., 30(4), 2011
Původní snímek · 45
References: BRDF representation
References
BRDF representation
•
Rusinkiewicz, S.M., A new change of variables for efficient BRDF
representation, Rendering techniques' 98, 1998, pp. 11,
•
Havran V., Filip J., Myzskowski K., Bidirectional Texture Function Compression
based on Multi-Level Vector Quantization. Computer Graphics Forum, vol.
29, no. 1, pp. 175-190, March 2010
BRDF representation
•
Rusinkiewicz, S.M., A new change of variables for efficient BRDF
representation, Rendering techniques' 98, 1998, pp. 11,
•
Havran V., Filip J., Myzskowski K., Bidirectional Texture Function Compression
based on Multi-Level Vector Quantization. Computer Graphics Forum, vol.
29, no. 1, pp. 175-190, March 2010
Původní snímek · 46
