Validation of Color Managed 3D Appearance Acquisition

Michael Goesele

Max-Planck-Institut für Informatik(MPI Informatik)

Vortrag im Rahmen des V3D2 Workshops

29.+30. November 2004 in Berlin

Michael Goesele

Acquired BRDF Model

rendered BRDF model of a carafe

Villeroy & Boch (Mettlach, 19th century)

Michael Goesele

Acquired BRDF Model

Which model is (more) correct?

Michael Goesele

Background: BRDF

bidirectional reflectance distribution function (BRDF)

ratio of reflected to incident radiance at one pointfor any pair of directions

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Michael Goesele

Background: BRDF Acquisition

based on acquisition system for spatially varying BRDFs[Lensch et al. 2003]

determine local reflection properties for each surface point uses Lafortune BRDF model [Lafortune 1997]

shown at previous V3D2 Workshops … iN

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Michael Goesele

Background: BRDF Acquisition

Michael Goesele

Validation Questions

How exact can this method capture describe the behavior of a real object?

How exact can we reproduce an objects appearance? How can this be achieved?

will be discussed in this talk

How good is the Lafortune model?

will not be discussed in this talk see e.g. [Ngan et al., SIGGRAPH Sketch 2004]

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Michael Goesele

Color and Computer Graphics

yes, we have color … it works (somehow) RGB is always the same (?) looks nice after some tuning …

more seriously … not the main concern, other technologies more important eye can adjust to bad color reproduction comparison to ground truth often not possible/required

an important issue for digitization!

Michael Goesele

Background: Color Management

goal: ensure correct color reproduction across devices used in graphical arts and printing industry defined profile connection space (PCS) with CIE XYZ or

CIE Lab color space profiles describe conversion to PCS for all devices

take limitations of devices into account

Michael Goesele

ICC Profile Generation

example: input profile capture known test target with camera

lighting conditions (spectrum) identical to finally used conditions

profile generated by(commercial) software

captures properties of camera lighting test target

Michael Goesele

Key Idea

introduce color management into BRDF acquisition and reproduction workflow convert input images into defined color space

(during HDR image generation) convert rendered images into output device color space

allows for objective assessment of quality of acquired models important for libraries, conservation, …

color management ensures best possible color reproduction takes limitations of devices into account

Michael Goesele

BRDF Acquisition Workflow

move to calibratedcolor space

move to outputcolor space

Michael Goesele

Accuracy of the Acquired Model

compare spectrophotometer measurements with BRDF model evaluated under same conditions illumination at 45°, observation at 0° (along surface normal) performs measurement in spectral domain can be converted to other color representations

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BRDF spectrophotometer

Michael Goesele

Accuracy of the Acquired Model

BRDF(CIEXYZ)

Spectrophotometer (CIEXYZ)

E

Bird yellow 59.41, 61.23, 14.58 61.40, 61.51, 13.42 4.158

Bird orange 42.28, 33.17, 8.02 43.73, 32.73, 5.95 7.923

Bird blue 34.99, 40.09,46.65 32.74, 37.48, 48.16 4.283

Bird white 68.79, 73.35, 61.04 76.67, 78.75, 58.77 7.168

Carafe blue 17.63, 18.67, 33.26 17.72, 19.34, 36.325 3.398

Carafe white 57.16, 58.33, 52.11 54.00, 56.23, 43.27 7.003

quality metric: E distance in CIELab color space 1 E just noticable color difference under perfect conditions

Michael Goesele

Accuracy of the Acquired Model

compare renderings with photographs captured under identical conditions

quality metric: E

0 E

50 E

Minerva of Arezzo(Florence, 3rd century B.C. or 1st century A.C.)

Michael Goesele

Accuracy of the Acquired Model

until now: only comparison of acquired model to ground truth data important for conservation, long term storage

further goal: include output devices in validation can we (physically) reproduce the object correctly?

Michael Goesele

Accuracy of Renderings

visual comparison between rendering (on screen, printout) and real object under identical conditions

all devices are calibrated no manual color adjustment was performed!

screen real object(color laser printer)

printout

Michael Goesele

Accuracy of Renderings

visual comparison between rendering (on screen, printout) and real object under identical conditions

Michael Goesele

Accuracy of Renderings

visual comparison between rendering (on screen, printout) and real object under identical conditions

Michael Goesele

Conclusion

color management integrated into BRDF acquisition and rendering pipeline enables quantitative and visual validation of results

correct color acquisition and rendering is important! approach:

acquire best possible model use best possible reproduction

important for long term storage reproduction technology improves (displays, printers, …) model should support these as far as possible

Michael Goesele

Future Work

improve quality of color management some colors are still quite problematic color management for HDR images?

ongoing work in the community

handling of high contrast, out-of-gamut colors tone mapping problem new display technologies (e.g., HDR display)

Michael Goesele

Thanks to … Hendrik Lensch DFG Schwerpunktprogramm V3D2 “Verteilte Vermittlung und

Verarbeitung digitaler Dokumente”

More information … Michael Goesele, Hendrik P. A. Lensch, Hans-Peter Seidel:

Validation of Color Managed 3D Appearance Acquisition.Proc. IS&T’s 12th Color Imaging Conference, pp. 265-270, 2004.

Hendrik P. A. Lensch, Jan Kautz, Michael Goesele, Wolfgang Heidrich, Hans-Peter Seidel:Image-Based Reconstruction of Spatial Appearance and Geometric Detail.ACM Transactions on Graphics, vol. 22, 2, pp. 234-257, 2003.